Adding upstream version 1.16.10.upstream/1.16.10upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

67 files changed, 5771 insertions, 0 deletions

diff --git a/src/compress/flate/deflate.go b/src/compress/flate/deflate.go
new file mode 100644
index 0000000..5500321
--- /dev/null
+++ b/src/compress/flate/deflate.go
@@ -0,0 +1,748 @@
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package flate
+
+import (
+	"fmt"
+	"io"
+	"math"
+)
+
+const (
+	NoCompression      = 0
+	BestSpeed          = 1
+	BestCompression    = 9
+	DefaultCompression = -1
+
+	// HuffmanOnly disables Lempel-Ziv match searching and only performs Huffman
+	// entropy encoding. This mode is useful in compressing data that has
+	// already been compressed with an LZ style algorithm (e.g. Snappy or LZ4)
+	// that lacks an entropy encoder. Compression gains are achieved when
+	// certain bytes in the input stream occur more frequently than others.
+	//
+	// Note that HuffmanOnly produces a compressed output that is
+	// RFC 1951 compliant. That is, any valid DEFLATE decompressor will
+	// continue to be able to decompress this output.
+	HuffmanOnly = -2
+)
+
+const (
+	logWindowSize = 15
+	windowSize    = 1 << logWindowSize
+	windowMask    = windowSize - 1
+
+	// The LZ77 step produces a sequence of literal tokens and <length, offset>
+	// pair tokens. The offset is also known as distance. The underlying wire
+	// format limits the range of lengths and offsets. For example, there are
+	// 256 legitimate lengths: those in the range [3, 258]. This package's
+	// compressor uses a higher minimum match length, enabling optimizations
+	// such as finding matches via 32-bit loads and compares.
+	baseMatchLength = 3       // The smallest match length per the RFC section 3.2.5
+	minMatchLength  = 4       // The smallest match length that the compressor actually emits
+	maxMatchLength  = 258     // The largest match length
+	baseMatchOffset = 1       // The smallest match offset
+	maxMatchOffset  = 1 << 15 // The largest match offset
+
+	// The maximum number of tokens we put into a single flate block, just to
+	// stop things from getting too large.
+	maxFlateBlockTokens = 1 << 14
+	maxStoreBlockSize   = 65535
+	hashBits            = 17 // After 17 performance degrades
+	hashSize            = 1 << hashBits
+	hashMask            = (1 << hashBits) - 1
+	maxHashOffset       = 1 << 24
+
+	skipNever = math.MaxInt32
+)
+
+type compressionLevel struct {
+	level, good, lazy, nice, chain, fastSkipHashing int
+}
+
+var levels = []compressionLevel{
+	{0, 0, 0, 0, 0, 0}, // NoCompression.
+	{1, 0, 0, 0, 0, 0}, // BestSpeed uses a custom algorithm; see deflatefast.go.
+	// For levels 2-3 we don't bother trying with lazy matches.
+	{2, 4, 0, 16, 8, 5},
+	{3, 4, 0, 32, 32, 6},
+	// Levels 4-9 use increasingly more lazy matching
+	// and increasingly stringent conditions for "good enough".
+	{4, 4, 4, 16, 16, skipNever},
+	{5, 8, 16, 32, 32, skipNever},
+	{6, 8, 16, 128, 128, skipNever},
+	{7, 8, 32, 128, 256, skipNever},
+	{8, 32, 128, 258, 1024, skipNever},
+	{9, 32, 258, 258, 4096, skipNever},
+}
+
+type compressor struct {
+	compressionLevel
+
+	w          *huffmanBitWriter
+	bulkHasher func([]byte, []uint32)
+
+	// compression algorithm
+	fill      func(*compressor, []byte) int // copy data to window
+	step      func(*compressor)             // process window
+	sync      bool                          // requesting flush
+	bestSpeed *deflateFast                  // Encoder for BestSpeed
+
+	// Input hash chains
+	// hashHead[hashValue] contains the largest inputIndex with the specified hash value
+	// If hashHead[hashValue] is within the current window, then
+	// hashPrev[hashHead[hashValue] & windowMask] contains the previous index
+	// with the same hash value.
+	chainHead  int
+	hashHead   [hashSize]uint32
+	hashPrev   [windowSize]uint32
+	hashOffset int
+
+	// input window: unprocessed data is window[index:windowEnd]
+	index         int
+	window        []byte
+	windowEnd     int
+	blockStart    int  // window index where current tokens start
+	byteAvailable bool // if true, still need to process window[index-1].
+
+	// queued output tokens
+	tokens []token
+
+	// deflate state
+	length         int
+	offset         int
+	hash           uint32
+	maxInsertIndex int
+	err            error
+
+	// hashMatch must be able to contain hashes for the maximum match length.
+	hashMatch [maxMatchLength - 1]uint32
+}
+
+func (d *compressor) fillDeflate(b []byte) int {
+	if d.index >= 2*windowSize-(minMatchLength+maxMatchLength) {
+		// shift the window by windowSize
+		copy(d.window, d.window[windowSize:2*windowSize])
+		d.index -= windowSize
+		d.windowEnd -= windowSize
+		if d.blockStart >= windowSize {
+			d.blockStart -= windowSize
+		} else {
+			d.blockStart = math.MaxInt32
+		}
+		d.hashOffset += windowSize
+		if d.hashOffset > maxHashOffset {
+			delta := d.hashOffset - 1
+			d.hashOffset -= delta
+			d.chainHead -= delta
+
+			// Iterate over slices instead of arrays to avoid copying
+			// the entire table onto the stack (Issue #18625).
+			for i, v := range d.hashPrev[:] {
+				if int(v) > delta {
+					d.hashPrev[i] = uint32(int(v) - delta)
+				} else {
+					d.hashPrev[i] = 0
+				}
+			}
+			for i, v := range d.hashHead[:] {
+				if int(v) > delta {
+					d.hashHead[i] = uint32(int(v) - delta)
+				} else {
+					d.hashHead[i] = 0
+				}
+			}
+		}
+	}
+	n := copy(d.window[d.windowEnd:], b)
+	d.windowEnd += n
+	return n
+}
+
+func (d *compressor) writeBlock(tokens []token, index int) error {
+	if index > 0 {
+		var window []byte
+		if d.blockStart <= index {
+			window = d.window[d.blockStart:index]
+		}
+		d.blockStart = index
+		d.w.writeBlock(tokens, false, window)
+		return d.w.err
+	}
+	return nil
+}
+
+// fillWindow will fill the current window with the supplied
+// dictionary and calculate all hashes.
+// This is much faster than doing a full encode.
+// Should only be used after a reset.
+func (d *compressor) fillWindow(b []byte) {
+	// Do not fill window if we are in store-only mode.
+	if d.compressionLevel.level < 2 {
+		return
+	}
+	if d.index != 0 || d.windowEnd != 0 {
+		panic("internal error: fillWindow called with stale data")
+	}
+
+	// If we are given too much, cut it.
+	if len(b) > windowSize {
+		b = b[len(b)-windowSize:]
+	}
+	// Add all to window.
+	n := copy(d.window, b)
+
+	// Calculate 256 hashes at the time (more L1 cache hits)
+	loops := (n + 256 - minMatchLength) / 256
+	for j := 0; j < loops; j++ {
+		index := j * 256
+		end := index + 256 + minMatchLength - 1
+		if end > n {
+			end = n
+		}
+		toCheck := d.window[index:end]
+		dstSize := len(toCheck) - minMatchLength + 1
+
+		if dstSize <= 0 {
+			continue
+		}
+
+		dst := d.hashMatch[:dstSize]
+		d.bulkHasher(toCheck, dst)
+		var newH uint32
+		for i, val := range dst {
+			di := i + index
+			newH = val
+			hh := &d.hashHead[newH&hashMask]
+			// Get previous value with the same hash.
+			// Our chain should point to the previous value.
+			d.hashPrev[di&windowMask] = *hh
+			// Set the head of the hash chain to us.
+			*hh = uint32(di + d.hashOffset)
+		}
+		d.hash = newH
+	}
+	// Update window information.
+	d.windowEnd = n
+	d.index = n
+}
+
+// Try to find a match starting at index whose length is greater than prevSize.
+// We only look at chainCount possibilities before giving up.
+func (d *compressor) findMatch(pos int, prevHead int, prevLength int, lookahead int) (length, offset int, ok bool) {
+	minMatchLook := maxMatchLength
+	if lookahead < minMatchLook {
+		minMatchLook = lookahead
+	}
+
+	win := d.window[0 : pos+minMatchLook]
+
+	// We quit when we get a match that's at least nice long
+	nice := len(win) - pos
+	if d.nice < nice {
+		nice = d.nice
+	}
+
+	// If we've got a match that's good enough, only look in 1/4 the chain.
+	tries := d.chain
+	length = prevLength
+	if length >= d.good {
+		tries >>= 2
+	}
+
+	wEnd := win[pos+length]
+	wPos := win[pos:]
+	minIndex := pos - windowSize
+
+	for i := prevHead; tries > 0; tries-- {
+		if wEnd == win[i+length] {
+			n := matchLen(win[i:], wPos, minMatchLook)
+
+			if n > length && (n > minMatchLength || pos-i <= 4096) {
+				length = n
+				offset = pos - i
+				ok = true
+				if n >= nice {
+					// The match is good enough that we don't try to find a better one.
+					break
+				}
+				wEnd = win[pos+n]
+			}
+		}
+		if i == minIndex {
+			// hashPrev[i & windowMask] has already been overwritten, so stop now.
+			break
+		}
+		i = int(d.hashPrev[i&windowMask]) - d.hashOffset
+		if i < minIndex || i < 0 {
+			break
+		}
+	}
+	return
+}
+
+func (d *compressor) writeStoredBlock(buf []byte) error {
+	if d.w.writeStoredHeader(len(buf), false); d.w.err != nil {
+		return d.w.err
+	}
+	d.w.writeBytes(buf)
+	return d.w.err
+}
+
+const hashmul = 0x1e35a7bd
+
+// hash4 returns a hash representation of the first 4 bytes
+// of the supplied slice.
+// The caller must ensure that len(b) >= 4.
+func hash4(b []byte) uint32 {
+	return ((uint32(b[3]) | uint32(b[2])<<8 | uint32(b[1])<<16 | uint32(b[0])<<24) * hashmul) >> (32 - hashBits)
+}
+
+// bulkHash4 will compute hashes using the same
+// algorithm as hash4
+func bulkHash4(b []byte, dst []uint32) {
+	if len(b) < minMatchLength {
+		return
+	}
+	hb := uint32(b[3]) | uint32(b[2])<<8 | uint32(b[1])<<16 | uint32(b[0])<<24
+	dst[0] = (hb * hashmul) >> (32 - hashBits)
+	end := len(b) - minMatchLength + 1
+	for i := 1; i < end; i++ {
+		hb = (hb << 8) | uint32(b[i+3])
+		dst[i] = (hb * hashmul) >> (32 - hashBits)
+	}
+}
+
+// matchLen returns the number of matching bytes in a and b
+// up to length 'max'. Both slices must be at least 'max'
+// bytes in size.
+func matchLen(a, b []byte, max int) int {
+	a = a[:max]
+	b = b[:len(a)]
+	for i, av := range a {
+		if b[i] != av {
+			return i
+		}
+	}
+	return max
+}
+
+// encSpeed will compress and store the currently added data,
+// if enough has been accumulated or we at the end of the stream.
+// Any error that occurred will be in d.err
+func (d *compressor) encSpeed() {
+	// We only compress if we have maxStoreBlockSize.
+	if d.windowEnd < maxStoreBlockSize {
+		if !d.sync {
+			return
+		}
+
+		// Handle small sizes.
+		if d.windowEnd < 128 {
+			switch {
+			case d.windowEnd == 0:
+				return
+			case d.windowEnd <= 16:
+				d.err = d.writeStoredBlock(d.window[:d.windowEnd])
+			default:
+				d.w.writeBlockHuff(false, d.window[:d.windowEnd])
+				d.err = d.w.err
+			}
+			d.windowEnd = 0
+			d.bestSpeed.reset()
+			return
+		}
+
+	}
+	// Encode the block.
+	d.tokens = d.bestSpeed.encode(d.tokens[:0], d.window[:d.windowEnd])
+
+	// If we removed less than 1/16th, Huffman compress the block.
+	if len(d.tokens) > d.windowEnd-(d.windowEnd>>4) {
+		d.w.writeBlockHuff(false, d.window[:d.windowEnd])
+	} else {
+		d.w.writeBlockDynamic(d.tokens, false, d.window[:d.windowEnd])
+	}
+	d.err = d.w.err
+	d.windowEnd = 0
+}
+
+func (d *compressor) initDeflate() {
+	d.window = make([]byte, 2*windowSize)
+	d.hashOffset = 1
+	d.tokens = make([]token, 0, maxFlateBlockTokens+1)
+	d.length = minMatchLength - 1
+	d.offset = 0
+	d.byteAvailable = false
+	d.index = 0
+	d.hash = 0
+	d.chainHead = -1
+	d.bulkHasher = bulkHash4
+}
+
+func (d *compressor) deflate() {
+	if d.windowEnd-d.index < minMatchLength+maxMatchLength && !d.sync {
+		return
+	}
+
+	d.maxInsertIndex = d.windowEnd - (minMatchLength - 1)
+	if d.index < d.maxInsertIndex {
+		d.hash = hash4(d.window[d.index : d.index+minMatchLength])
+	}
+
+Loop:
+	for {
+		if d.index > d.windowEnd {
+			panic("index > windowEnd")
+		}
+		lookahead := d.windowEnd - d.index
+		if lookahead < minMatchLength+maxMatchLength {
+			if !d.sync {
+				break Loop
+			}
+			if d.index > d.windowEnd {
+				panic("index > windowEnd")
+			}
+			if lookahead == 0 {
+				// Flush current output block if any.
+				if d.byteAvailable {
+					// There is still one pending token that needs to be flushed
+					d.tokens = append(d.tokens, literalToken(uint32(d.window[d.index-1])))
+					d.byteAvailable = false
+				}
+				if len(d.tokens) > 0 {
+					if d.err = d.writeBlock(d.tokens, d.index); d.err != nil {
+						return
+					}
+					d.tokens = d.tokens[:0]
+				}
+				break Loop
+			}
+		}
+		if d.index < d.maxInsertIndex {
+			// Update the hash
+			d.hash = hash4(d.window[d.index : d.index+minMatchLength])
+			hh := &d.hashHead[d.hash&hashMask]
+			d.chainHead = int(*hh)
+			d.hashPrev[d.index&windowMask] = uint32(d.chainHead)
+			*hh = uint32(d.index + d.hashOffset)
+		}
+		prevLength := d.length
+		prevOffset := d.offset
+		d.length = minMatchLength - 1
+		d.offset = 0
+		minIndex := d.index - windowSize
+		if minIndex < 0 {
+			minIndex = 0
+		}
+
+		if d.chainHead-d.hashOffset >= minIndex &&
+			(d.fastSkipHashing != skipNever && lookahead > minMatchLength-1 ||
+				d.fastSkipHashing == skipNever && lookahead > prevLength && prevLength < d.lazy) {
+			if newLength, newOffset, ok := d.findMatch(d.index, d.chainHead-d.hashOffset, minMatchLength-1, lookahead); ok {
+				d.length = newLength
+				d.offset = newOffset
+			}
+		}
+		if d.fastSkipHashing != skipNever && d.length >= minMatchLength ||
+			d.fastSkipHashing == skipNever && prevLength >= minMatchLength && d.length <= prevLength {
+			// There was a match at the previous step, and the current match is
+			// not better. Output the previous match.
+			if d.fastSkipHashing != skipNever {
+				d.tokens = append(d.tokens, matchToken(uint32(d.length-baseMatchLength), uint32(d.offset-baseMatchOffset)))
+			} else {
+				d.tokens = append(d.tokens, matchToken(uint32(prevLength-baseMatchLength), uint32(prevOffset-baseMatchOffset)))
+			}
+			// Insert in the hash table all strings up to the end of the match.
+			// index and index-1 are already inserted. If there is not enough
+			// lookahead, the last two strings are not inserted into the hash
+			// table.
+			if d.length <= d.fastSkipHashing {
+				var newIndex int
+				if d.fastSkipHashing != skipNever {
+					newIndex = d.index + d.length
+				} else {
+					newIndex = d.index + prevLength - 1
+				}
+				index := d.index
+				for index++; index < newIndex; index++ {
+					if index < d.maxInsertIndex {
+						d.hash = hash4(d.window[index : index+minMatchLength])
+						// Get previous value with the same hash.
+						// Our chain should point to the previous value.
+						hh := &d.hashHead[d.hash&hashMask]
+						d.hashPrev[index&windowMask] = *hh
+						// Set the head of the hash chain to us.
+						*hh = uint32(index + d.hashOffset)
+					}
+				}
+				d.index = index
+
+				if d.fastSkipHashing == skipNever {
+					d.byteAvailable = false
+					d.length = minMatchLength - 1
+				}
+			} else {
+				// For matches this long, we don't bother inserting each individual
+				// item into the table.
+				d.index += d.length
+				if d.index < d.maxInsertIndex {
+					d.hash = hash4(d.window[d.index : d.index+minMatchLength])
+				}
+			}
+			if len(d.tokens) == maxFlateBlockTokens {
+				// The block includes the current character
+				if d.err = d.writeBlock(d.tokens, d.index); d.err != nil {
+					return
+				}
+				d.tokens = d.tokens[:0]
+			}
+		} else {
+			if d.fastSkipHashing != skipNever || d.byteAvailable {
+				i := d.index - 1
+				if d.fastSkipHashing != skipNever {
+					i = d.index
+				}
+				d.tokens = append(d.tokens, literalToken(uint32(d.window[i])))
+				if len(d.tokens) == maxFlateBlockTokens {
+					if d.err = d.writeBlock(d.tokens, i+1); d.err != nil {
+						return
+					}
+					d.tokens = d.tokens[:0]
+				}
+			}
+			d.index++
+			if d.fastSkipHashing == skipNever {
+				d.byteAvailable = true
+			}
+		}
+	}
+}
+
+func (d *compressor) fillStore(b []byte) int {
+	n := copy(d.window[d.windowEnd:], b)
+	d.windowEnd += n
+	return n
+}
+
+func (d *compressor) store() {
+	if d.windowEnd > 0 && (d.windowEnd == maxStoreBlockSize || d.sync) {
+		d.err = d.writeStoredBlock(d.window[:d.windowEnd])
+		d.windowEnd = 0
+	}
+}
+
+// storeHuff compresses and stores the currently added data
+// when the d.window is full or we are at the end of the stream.
+// Any error that occurred will be in d.err
+func (d *compressor) storeHuff() {
+	if d.windowEnd < len(d.window) && !d.sync || d.windowEnd == 0 {
+		return
+	}
+	d.w.writeBlockHuff(false, d.window[:d.windowEnd])
+	d.err = d.w.err
+	d.windowEnd = 0
+}
+
+func (d *compressor) write(b []byte) (n int, err error) {
+	if d.err != nil {
+		return 0, d.err
+	}
+	n = len(b)
+	for len(b) > 0 {
+		d.step(d)
+		b = b[d.fill(d, b):]
+		if d.err != nil {
+			return 0, d.err
+		}
+	}
+	return n, nil
+}
+
+func (d *compressor) syncFlush() error {
+	if d.err != nil {
+		return d.err
+	}
+	d.sync = true
+	d.step(d)
+	if d.err == nil {
+		d.w.writeStoredHeader(0, false)
+		d.w.flush()
+		d.err = d.w.err
+	}
+	d.sync = false
+	return d.err
+}
+
+func (d *compressor) init(w io.Writer, level int) (err error) {
+	d.w = newHuffmanBitWriter(w)
+
+	switch {
+	case level == NoCompression:
+		d.window = make([]byte, maxStoreBlockSize)
+		d.fill = (*compressor).fillStore
+		d.step = (*compressor).store
+	case level == HuffmanOnly:
+		d.window = make([]byte, maxStoreBlockSize)
+		d.fill = (*compressor).fillStore
+		d.step = (*compressor).storeHuff
+	case level == BestSpeed:
+		d.compressionLevel = levels[level]
+		d.window = make([]byte, maxStoreBlockSize)
+		d.fill = (*compressor).fillStore
+		d.step = (*compressor).encSpeed
+		d.bestSpeed = newDeflateFast()
+		d.tokens = make([]token, maxStoreBlockSize)
+	case level == DefaultCompression:
+		level = 6
+		fallthrough
+	case 2 <= level && level <= 9:
+		d.compressionLevel = levels[level]
+		d.initDeflate()
+		d.fill = (*compressor).fillDeflate
+		d.step = (*compressor).deflate
+	default:
+		return fmt.Errorf("flate: invalid compression level %d: want value in range [-2, 9]", level)
+	}
+	return nil
+}
+
+func (d *compressor) reset(w io.Writer) {
+	d.w.reset(w)
+	d.sync = false
+	d.err = nil
+	switch d.compressionLevel.level {
+	case NoCompression:
+		d.windowEnd = 0
+	case BestSpeed:
+		d.windowEnd = 0
+		d.tokens = d.tokens[:0]
+		d.bestSpeed.reset()
+	default:
+		d.chainHead = -1
+		for i := range d.hashHead {
+			d.hashHead[i] = 0
+		}
+		for i := range d.hashPrev {
+			d.hashPrev[i] = 0
+		}
+		d.hashOffset = 1
+		d.index, d.windowEnd = 0, 0
+		d.blockStart, d.byteAvailable = 0, false
+		d.tokens = d.tokens[:0]
+		d.length = minMatchLength - 1
+		d.offset = 0
+		d.hash = 0
+		d.maxInsertIndex = 0
+	}
+}
+
+func (d *compressor) close() error {
+	if d.err != nil {
+		return d.err
+	}
+	d.sync = true
+	d.step(d)
+	if d.err != nil {
+		return d.err
+	}
+	if d.w.writeStoredHeader(0, true); d.w.err != nil {
+		return d.w.err
+	}
+	d.w.flush()
+	return d.w.err
+}
+
+// NewWriter returns a new Writer compressing data at the given level.
+// Following zlib, levels range from 1 (BestSpeed) to 9 (BestCompression);
+// higher levels typically run slower but compress more. Level 0
+// (NoCompression) does not attempt any compression; it only adds the
+// necessary DEFLATE framing.
+// Level -1 (DefaultCompression) uses the default compression level.
+// Level -2 (HuffmanOnly) will use Huffman compression only, giving
+// a very fast compression for all types of input, but sacrificing considerable
+// compression efficiency.
+//
+// If level is in the range [-2, 9] then the error returned will be nil.
+// Otherwise the error returned will be non-nil.
+func NewWriter(w io.Writer, level int) (*Writer, error) {
+	var dw Writer
+	if err := dw.d.init(w, level); err != nil {
+		return nil, err
+	}
+	return &dw, nil
+}
+
+// NewWriterDict is like NewWriter but initializes the new
+// Writer with a preset dictionary. The returned Writer behaves
+// as if the dictionary had been written to it without producing
+// any compressed output. The compressed data written to w
+// can only be decompressed by a Reader initialized with the
+// same dictionary.
+func NewWriterDict(w io.Writer, level int, dict []byte) (*Writer, error) {
+	dw := &dictWriter{w}
+	zw, err := NewWriter(dw, level)
+	if err != nil {
+		return nil, err
+	}
+	zw.d.fillWindow(dict)
+	zw.dict = append(zw.dict, dict...) // duplicate dictionary for Reset method.
+	return zw, err
+}
+
+type dictWriter struct {
+	w io.Writer
+}
+
+func (w *dictWriter) Write(b []byte) (n int, err error) {
+	return w.w.Write(b)
+}
+
+// A Writer takes data written to it and writes the compressed
+// form of that data to an underlying writer (see NewWriter).
+type Writer struct {
+	d    compressor
+	dict []byte
+}
+
+// Write writes data to w, which will eventually write the
+// compressed form of data to its underlying writer.
+func (w *Writer) Write(data []byte) (n int, err error) {
+	return w.d.write(data)
+}
+
+// Flush flushes any pending data to the underlying writer.
+// It is useful mainly in compressed network protocols, to ensure that
+// a remote reader has enough data to reconstruct a packet.
+// Flush does not return until the data has been written.
+// Calling Flush when there is no pending data still causes the Writer
+// to emit a sync marker of at least 4 bytes.
+// If the underlying writer returns an error, Flush returns that error.
+//
+// In the terminology of the zlib library, Flush is equivalent to Z_SYNC_FLUSH.
+func (w *Writer) Flush() error {
+	// For more about flushing:
+	// https://www.bolet.org/~pornin/deflate-flush.html
+	return w.d.syncFlush()
+}
+
+// Close flushes and closes the writer.
+func (w *Writer) Close() error {
+	return w.d.close()
+}
+
+// Reset discards the writer's state and makes it equivalent to
+// the result of NewWriter or NewWriterDict called with dst
+// and w's level and dictionary.
+func (w *Writer) Reset(dst io.Writer) {
+	if dw, ok := w.d.w.writer.(*dictWriter); ok {
+		// w was created with NewWriterDict
+		dw.w = dst
+		w.d.reset(dw)
+		w.d.fillWindow(w.dict)
+	} else {
+		// w was created with NewWriter
+		w.d.reset(dst)
+	}
+}
diff --git a/src/compress/flate/deflate_test.go b/src/compress/flate/deflate_test.go
new file mode 100644
index 0000000..ff56712
--- /dev/null
+++ b/src/compress/flate/deflate_test.go
@@ -0,0 +1,984 @@
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package flate
+
+import (
+	"bytes"
+	"errors"
+	"fmt"
+	"internal/testenv"
+	"io"
+	"math/rand"
+	"os"
+	"reflect"
+	"runtime/debug"
+	"sync"
+	"testing"
+)
+
+type deflateTest struct {
+	in    []byte
+	level int
+	out   []byte
+}
+
+type deflateInflateTest struct {
+	in []byte
+}
+
+type reverseBitsTest struct {
+	in       uint16
+	bitCount uint8
+	out      uint16
+}
+
+var deflateTests = []*deflateTest{
+	{[]byte{}, 0, []byte{1, 0, 0, 255, 255}},
+	{[]byte{0x11}, -1, []byte{18, 4, 4, 0, 0, 255, 255}},
+	{[]byte{0x11}, DefaultCompression, []byte{18, 4, 4, 0, 0, 255, 255}},
+	{[]byte{0x11}, 4, []byte{18, 4, 4, 0, 0, 255, 255}},
+
+	{[]byte{0x11}, 0, []byte{0, 1, 0, 254, 255, 17, 1, 0, 0, 255, 255}},
+	{[]byte{0x11, 0x12}, 0, []byte{0, 2, 0, 253, 255, 17, 18, 1, 0, 0, 255, 255}},
+	{[]byte{0x11, 0x11, 0x11, 0x11, 0x11, 0x11, 0x11, 0x11}, 0,
+		[]byte{0, 8, 0, 247, 255, 17, 17, 17, 17, 17, 17, 17, 17, 1, 0, 0, 255, 255},
+	},
+	{[]byte{}, 2, []byte{1, 0, 0, 255, 255}},
+	{[]byte{0x11}, 2, []byte{18, 4, 4, 0, 0, 255, 255}},
+	{[]byte{0x11, 0x12}, 2, []byte{18, 20, 2, 4, 0, 0, 255, 255}},
+	{[]byte{0x11, 0x11, 0x11, 0x11, 0x11, 0x11, 0x11, 0x11}, 2, []byte{18, 132, 2, 64, 0, 0, 0, 255, 255}},
+	{[]byte{}, 9, []byte{1, 0, 0, 255, 255}},
+	{[]byte{0x11}, 9, []byte{18, 4, 4, 0, 0, 255, 255}},
+	{[]byte{0x11, 0x12}, 9, []byte{18, 20, 2, 4, 0, 0, 255, 255}},
+	{[]byte{0x11, 0x11, 0x11, 0x11, 0x11, 0x11, 0x11, 0x11}, 9, []byte{18, 132, 2, 64, 0, 0, 0, 255, 255}},
+}
+
+var deflateInflateTests = []*deflateInflateTest{
+	{[]byte{}},
+	{[]byte{0x11}},
+	{[]byte{0x11, 0x12}},
+	{[]byte{0x11, 0x11, 0x11, 0x11, 0x11, 0x11, 0x11, 0x11}},
+	{[]byte{0x11, 0x10, 0x13, 0x41, 0x21, 0x21, 0x41, 0x13, 0x87, 0x78, 0x13}},
+	{largeDataChunk()},
+}
+
+var reverseBitsTests = []*reverseBitsTest{
+	{1, 1, 1},
+	{1, 2, 2},
+	{1, 3, 4},
+	{1, 4, 8},
+	{1, 5, 16},
+	{17, 5, 17},
+	{257, 9, 257},
+	{29, 5, 23},
+}
+
+func largeDataChunk() []byte {
+	result := make([]byte, 100000)
+	for i := range result {
+		result[i] = byte(i * i & 0xFF)
+	}
+	return result
+}
+
+func TestBulkHash4(t *testing.T) {
+	for _, x := range deflateTests {
+		y := x.out
+		if len(y) < minMatchLength {
+			continue
+		}
+		y = append(y, y...)
+		for j := 4; j < len(y); j++ {
+			y := y[:j]
+			dst := make([]uint32, len(y)-minMatchLength+1)
+			for i := range dst {
+				dst[i] = uint32(i + 100)
+			}
+			bulkHash4(y, dst)
+			for i, got := range dst {
+				want := hash4(y[i:])
+				if got != want && got == uint32(i)+100 {
+					t.Errorf("Len:%d Index:%d, want 0x%08x but not modified", len(y), i, want)
+				} else if got != want {
+					t.Errorf("Len:%d Index:%d, got 0x%08x want:0x%08x", len(y), i, got, want)
+				}
+			}
+		}
+	}
+}
+
+func TestDeflate(t *testing.T) {
+	for _, h := range deflateTests {
+		var buf bytes.Buffer
+		w, err := NewWriter(&buf, h.level)
+		if err != nil {
+			t.Errorf("NewWriter: %v", err)
+			continue
+		}
+		w.Write(h.in)
+		w.Close()
+		if !bytes.Equal(buf.Bytes(), h.out) {
+			t.Errorf("Deflate(%d, %x) = \n%#v, want \n%#v", h.level, h.in, buf.Bytes(), h.out)
+		}
+	}
+}
+
+// A sparseReader returns a stream consisting of 0s followed by 1<<16 1s.
+// This tests missing hash references in a very large input.
+type sparseReader struct {
+	l   int64
+	cur int64
+}
+
+func (r *sparseReader) Read(b []byte) (n int, err error) {
+	if r.cur >= r.l {
+		return 0, io.EOF
+	}
+	n = len(b)
+	cur := r.cur + int64(n)
+	if cur > r.l {
+		n -= int(cur - r.l)
+		cur = r.l
+	}
+	for i := range b[0:n] {
+		if r.cur+int64(i) >= r.l-1<<16 {
+			b[i] = 1
+		} else {
+			b[i] = 0
+		}
+	}
+	r.cur = cur
+	return
+}
+
+func TestVeryLongSparseChunk(t *testing.T) {
+	if testing.Short() {
+		t.Skip("skipping sparse chunk during short test")
+	}
+	w, err := NewWriter(io.Discard, 1)
+	if err != nil {
+		t.Errorf("NewWriter: %v", err)
+		return
+	}
+	if _, err = io.Copy(w, &sparseReader{l: 23e8}); err != nil {
+		t.Errorf("Compress failed: %v", err)
+		return
+	}
+}
+
+type syncBuffer struct {
+	buf    bytes.Buffer
+	mu     sync.RWMutex
+	closed bool
+	ready  chan bool
+}
+
+func newSyncBuffer() *syncBuffer {
+	return &syncBuffer{ready: make(chan bool, 1)}
+}
+
+func (b *syncBuffer) Read(p []byte) (n int, err error) {
+	for {
+		b.mu.RLock()
+		n, err = b.buf.Read(p)
+		b.mu.RUnlock()
+		if n > 0 || b.closed {
+			return
+		}
+		<-b.ready
+	}
+}
+
+func (b *syncBuffer) signal() {
+	select {
+	case b.ready <- true:
+	default:
+	}
+}
+
+func (b *syncBuffer) Write(p []byte) (n int, err error) {
+	n, err = b.buf.Write(p)
+	b.signal()
+	return
+}
+
+func (b *syncBuffer) WriteMode() {
+	b.mu.Lock()
+}
+
+func (b *syncBuffer) ReadMode() {
+	b.mu.Unlock()
+	b.signal()
+}
+
+func (b *syncBuffer) Close() error {
+	b.closed = true
+	b.signal()
+	return nil
+}
+
+func testSync(t *testing.T, level int, input []byte, name string) {
+	if len(input) == 0 {
+		return
+	}
+
+	t.Logf("--testSync %d, %d, %s", level, len(input), name)
+	buf := newSyncBuffer()
+	buf1 := new(bytes.Buffer)
+	buf.WriteMode()
+	w, err := NewWriter(io.MultiWriter(buf, buf1), level)
+	if err != nil {
+		t.Errorf("NewWriter: %v", err)
+		return
+	}
+	r := NewReader(buf)
+
+	// Write half the input and read back.
+	for i := 0; i < 2; i++ {
+		var lo, hi int
+		if i == 0 {
+			lo, hi = 0, (len(input)+1)/2
+		} else {
+			lo, hi = (len(input)+1)/2, len(input)
+		}
+		t.Logf("#%d: write %d-%d", i, lo, hi)
+		if _, err := w.Write(input[lo:hi]); err != nil {
+			t.Errorf("testSync: write: %v", err)
+			return
+		}
+		if i == 0 {
+			if err := w.Flush(); err != nil {
+				t.Errorf("testSync: flush: %v", err)
+				return
+			}
+		} else {
+			if err := w.Close(); err != nil {
+				t.Errorf("testSync: close: %v", err)
+			}
+		}
+		buf.ReadMode()
+		out := make([]byte, hi-lo+1)
+		m, err := io.ReadAtLeast(r, out, hi-lo)
+		t.Logf("#%d: read %d", i, m)
+		if m != hi-lo || err != nil {
+			t.Errorf("testSync/%d (%d, %d, %s): read %d: %d, %v (%d left)", i, level, len(input), name, hi-lo, m, err, buf.buf.Len())
+			return
+		}
+		if !bytes.Equal(input[lo:hi], out[:hi-lo]) {
+			t.Errorf("testSync/%d: read wrong bytes: %x vs %x", i, input[lo:hi], out[:hi-lo])
+			return
+		}
+		// This test originally checked that after reading
+		// the first half of the input, there was nothing left
+		// in the read buffer (buf.buf.Len() != 0) but that is
+		// not necessarily the case: the write Flush may emit
+		// some extra framing bits that are not necessary
+		// to process to obtain the first half of the uncompressed
+		// data. The test ran correctly most of the time, because
+		// the background goroutine had usually read even
+		// those extra bits by now, but it's not a useful thing to
+		// check.
+		buf.WriteMode()
+	}
+	buf.ReadMode()
+	out := make([]byte, 10)
+	if n, err := r.Read(out); n > 0 || err != io.EOF {
+		t.Errorf("testSync (%d, %d, %s): final Read: %d, %v (hex: %x)", level, len(input), name, n, err, out[0:n])
+	}
+	if buf.buf.Len() != 0 {
+		t.Errorf("testSync (%d, %d, %s): extra data at end", level, len(input), name)
+	}
+	r.Close()
+
+	// stream should work for ordinary reader too
+	r = NewReader(buf1)
+	out, err = io.ReadAll(r)
+	if err != nil {
+		t.Errorf("testSync: read: %s", err)
+		return
+	}
+	r.Close()
+	if !bytes.Equal(input, out) {
+		t.Errorf("testSync: decompress(compress(data)) != data: level=%d input=%s", level, name)
+	}
+}
+
+func testToFromWithLevelAndLimit(t *testing.T, level int, input []byte, name string, limit int) {
+	var buffer bytes.Buffer
+	w, err := NewWriter(&buffer, level)
+	if err != nil {
+		t.Errorf("NewWriter: %v", err)
+		return
+	}
+	w.Write(input)
+	w.Close()
+	if limit > 0 && buffer.Len() > limit {
+		t.Errorf("level: %d, len(compress(data)) = %d > limit = %d", level, buffer.Len(), limit)
+		return
+	}
+	if limit > 0 {
+		t.Logf("level: %d, size:%.2f%%, %d b\n", level, float64(buffer.Len()*100)/float64(limit), buffer.Len())
+	}
+	r := NewReader(&buffer)
+	out, err := io.ReadAll(r)
+	if err != nil {
+		t.Errorf("read: %s", err)
+		return
+	}
+	r.Close()
+	if !bytes.Equal(input, out) {
+		t.Errorf("decompress(compress(data)) != data: level=%d input=%s", level, name)
+		return
+	}
+	testSync(t, level, input, name)
+}
+
+func testToFromWithLimit(t *testing.T, input []byte, name string, limit [11]int) {
+	for i := 0; i < 10; i++ {
+		testToFromWithLevelAndLimit(t, i, input, name, limit[i])
+	}
+	// Test HuffmanCompression
+	testToFromWithLevelAndLimit(t, -2, input, name, limit[10])
+}
+
+func TestDeflateInflate(t *testing.T) {
+	t.Parallel()
+	for i, h := range deflateInflateTests {
+		if testing.Short() && len(h.in) > 10000 {
+			continue
+		}
+		testToFromWithLimit(t, h.in, fmt.Sprintf("#%d", i), [11]int{})
+	}
+}
+
+func TestReverseBits(t *testing.T) {
+	for _, h := range reverseBitsTests {
+		if v := reverseBits(h.in, h.bitCount); v != h.out {
+			t.Errorf("reverseBits(%v,%v) = %v, want %v",
+				h.in, h.bitCount, v, h.out)
+		}
+	}
+}
+
+type deflateInflateStringTest struct {
+	filename string
+	label    string
+	limit    [11]int
+}
+
+var deflateInflateStringTests = []deflateInflateStringTest{
+	{
+		"../testdata/e.txt",
+		"2.718281828...",
+		[...]int{100018, 50650, 50960, 51150, 50930, 50790, 50790, 50790, 50790, 50790, 43683},
+	},
+	{
+		"../../testdata/Isaac.Newton-Opticks.txt",
+		"Isaac.Newton-Opticks",
+		[...]int{567248, 218338, 198211, 193152, 181100, 175427, 175427, 173597, 173422, 173422, 325240},
+	},
+}
+
+func TestDeflateInflateString(t *testing.T) {
+	t.Parallel()
+	if testing.Short() && testenv.Builder() == "" {
+		t.Skip("skipping in short mode")
+	}
+	for _, test := range deflateInflateStringTests {
+		gold, err := os.ReadFile(test.filename)
+		if err != nil {
+			t.Error(err)
+		}
+		testToFromWithLimit(t, gold, test.label, test.limit)
+		if testing.Short() {
+			break
+		}
+	}
+}
+
+func TestReaderDict(t *testing.T) {
+	const (
+		dict = "hello world"
+		text = "hello again world"
+	)
+	var b bytes.Buffer
+	w, err := NewWriter(&b, 5)
+	if err != nil {
+		t.Fatalf("NewWriter: %v", err)
+	}
+	w.Write([]byte(dict))
+	w.Flush()
+	b.Reset()
+	w.Write([]byte(text))
+	w.Close()
+
+	r := NewReaderDict(&b, []byte(dict))
+	data, err := io.ReadAll(r)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if string(data) != "hello again world" {
+		t.Fatalf("read returned %q want %q", string(data), text)
+	}
+}
+
+func TestWriterDict(t *testing.T) {
+	const (
+		dict = "hello world"
+		text = "hello again world"
+	)
+	var b bytes.Buffer
+	w, err := NewWriter(&b, 5)
+	if err != nil {
+		t.Fatalf("NewWriter: %v", err)
+	}
+	w.Write([]byte(dict))
+	w.Flush()
+	b.Reset()
+	w.Write([]byte(text))
+	w.Close()
+
+	var b1 bytes.Buffer
+	w, _ = NewWriterDict(&b1, 5, []byte(dict))
+	w.Write([]byte(text))
+	w.Close()
+
+	if !bytes.Equal(b1.Bytes(), b.Bytes()) {
+		t.Fatalf("writer wrote %q want %q", b1.Bytes(), b.Bytes())
+	}
+}
+
+// See https://golang.org/issue/2508
+func TestRegression2508(t *testing.T) {
+	if testing.Short() {
+		t.Logf("test disabled with -short")
+		return
+	}
+	w, err := NewWriter(io.Discard, 1)
+	if err != nil {
+		t.Fatalf("NewWriter: %v", err)
+	}
+	buf := make([]byte, 1024)
+	for i := 0; i < 131072; i++ {
+		if _, err := w.Write(buf); err != nil {
+			t.Fatalf("writer failed: %v", err)
+		}
+	}
+	w.Close()
+}
+
+func TestWriterReset(t *testing.T) {
+	t.Parallel()
+	for level := 0; level <= 9; level++ {
+		if testing.Short() && level > 1 {
+			break
+		}
+		w, err := NewWriter(io.Discard, level)
+		if err != nil {
+			t.Fatalf("NewWriter: %v", err)
+		}
+		buf := []byte("hello world")
+		n := 1024
+		if testing.Short() {
+			n = 10
+		}
+		for i := 0; i < n; i++ {
+			w.Write(buf)
+		}
+		w.Reset(io.Discard)
+
+		wref, err := NewWriter(io.Discard, level)
+		if err != nil {
+			t.Fatalf("NewWriter: %v", err)
+		}
+
+		// DeepEqual doesn't compare functions.
+		w.d.fill, wref.d.fill = nil, nil
+		w.d.step, wref.d.step = nil, nil
+		w.d.bulkHasher, wref.d.bulkHasher = nil, nil
+		w.d.bestSpeed, wref.d.bestSpeed = nil, nil
+		// hashMatch is always overwritten when used.
+		copy(w.d.hashMatch[:], wref.d.hashMatch[:])
+		if len(w.d.tokens) != 0 {
+			t.Errorf("level %d Writer not reset after Reset. %d tokens were present", level, len(w.d.tokens))
+		}
+		// As long as the length is 0, we don't care about the content.
+		w.d.tokens = wref.d.tokens
+
+		// We don't care if there are values in the window, as long as it is at d.index is 0
+		w.d.window = wref.d.window
+		if !reflect.DeepEqual(w, wref) {
+			t.Errorf("level %d Writer not reset after Reset", level)
+		}
+	}
+
+	levels := []int{0, 1, 2, 5, 9}
+	for _, level := range levels {
+		t.Run(fmt.Sprint(level), func(t *testing.T) {
+			testResetOutput(t, level, nil)
+		})
+	}
+
+	t.Run("dict", func(t *testing.T) {
+		for _, level := range levels {
+			t.Run(fmt.Sprint(level), func(t *testing.T) {
+				testResetOutput(t, level, nil)
+			})
+		}
+	})
+}
+
+func testResetOutput(t *testing.T, level int, dict []byte) {
+	writeData := func(w *Writer) {
+		msg := []byte("now is the time for all good gophers")
+		w.Write(msg)
+		w.Flush()
+
+		hello := []byte("hello world")
+		for i := 0; i < 1024; i++ {
+			w.Write(hello)
+		}
+
+		fill := bytes.Repeat([]byte("x"), 65000)
+		w.Write(fill)
+	}
+
+	buf := new(bytes.Buffer)
+	var w *Writer
+	var err error
+	if dict == nil {
+		w, err = NewWriter(buf, level)
+	} else {
+		w, err = NewWriterDict(buf, level, dict)
+	}
+	if err != nil {
+		t.Fatalf("NewWriter: %v", err)
+	}
+
+	writeData(w)
+	w.Close()
+	out1 := buf.Bytes()
+
+	buf2 := new(bytes.Buffer)
+	w.Reset(buf2)
+	writeData(w)
+	w.Close()
+	out2 := buf2.Bytes()
+
+	if len(out1) != len(out2) {
+		t.Errorf("got %d, expected %d bytes", len(out2), len(out1))
+		return
+	}
+	if !bytes.Equal(out1, out2) {
+		mm := 0
+		for i, b := range out1[:len(out2)] {
+			if b != out2[i] {
+				t.Errorf("mismatch index %d: %#02x, expected %#02x", i, out2[i], b)
+			}
+			mm++
+			if mm == 10 {
+				t.Fatal("Stopping")
+			}
+		}
+	}
+	t.Logf("got %d bytes", len(out1))
+}
+
+// TestBestSpeed tests that round-tripping through deflate and then inflate
+// recovers the original input. The Write sizes are near the thresholds in the
+// compressor.encSpeed method (0, 16, 128), as well as near maxStoreBlockSize
+// (65535).
+func TestBestSpeed(t *testing.T) {
+	t.Parallel()
+	abc := make([]byte, 128)
+	for i := range abc {
+		abc[i] = byte(i)
+	}
+	abcabc := bytes.Repeat(abc, 131072/len(abc))
+	var want []byte
+
+	testCases := [][]int{
+		{65536, 0},
+		{65536, 1},
+		{65536, 1, 256},
+		{65536, 1, 65536},
+		{65536, 14},
+		{65536, 15},
+		{65536, 16},
+		{65536, 16, 256},
+		{65536, 16, 65536},
+		{65536, 127},
+		{65536, 128},
+		{65536, 128, 256},
+		{65536, 128, 65536},
+		{65536, 129},
+		{65536, 65536, 256},
+		{65536, 65536, 65536},
+	}
+
+	for i, tc := range testCases {
+		if i >= 3 && testing.Short() {
+			break
+		}
+		for _, firstN := range []int{1, 65534, 65535, 65536, 65537, 131072} {
+			tc[0] = firstN
+		outer:
+			for _, flush := range []bool{false, true} {
+				buf := new(bytes.Buffer)
+				want = want[:0]
+
+				w, err := NewWriter(buf, BestSpeed)
+				if err != nil {
+					t.Errorf("i=%d, firstN=%d, flush=%t: NewWriter: %v", i, firstN, flush, err)
+					continue
+				}
+				for _, n := range tc {
+					want = append(want, abcabc[:n]...)
+					if _, err := w.Write(abcabc[:n]); err != nil {
+						t.Errorf("i=%d, firstN=%d, flush=%t: Write: %v", i, firstN, flush, err)
+						continue outer
+					}
+					if !flush {
+						continue
+					}
+					if err := w.Flush(); err != nil {
+						t.Errorf("i=%d, firstN=%d, flush=%t: Flush: %v", i, firstN, flush, err)
+						continue outer
+					}
+				}
+				if err := w.Close(); err != nil {
+					t.Errorf("i=%d, firstN=%d, flush=%t: Close: %v", i, firstN, flush, err)
+					continue
+				}
+
+				r := NewReader(buf)
+				got, err := io.ReadAll(r)
+				if err != nil {
+					t.Errorf("i=%d, firstN=%d, flush=%t: ReadAll: %v", i, firstN, flush, err)
+					continue
+				}
+				r.Close()
+
+				if !bytes.Equal(got, want) {
+					t.Errorf("i=%d, firstN=%d, flush=%t: corruption during deflate-then-inflate", i, firstN, flush)
+					continue
+				}
+			}
+		}
+	}
+}
+
+var errIO = errors.New("IO error")
+
+// failWriter fails with errIO exactly at the nth call to Write.
+type failWriter struct{ n int }
+
+func (w *failWriter) Write(b []byte) (int, error) {
+	w.n--
+	if w.n == -1 {
+		return 0, errIO
+	}
+	return len(b), nil
+}
+
+func TestWriterPersistentError(t *testing.T) {
+	t.Parallel()
+	d, err := os.ReadFile("../../testdata/Isaac.Newton-Opticks.txt")
+	if err != nil {
+		t.Fatalf("ReadFile: %v", err)
+	}
+	d = d[:10000] // Keep this test short
+
+	zw, err := NewWriter(nil, DefaultCompression)
+	if err != nil {
+		t.Fatalf("NewWriter: %v", err)
+	}
+
+	// Sweep over the threshold at which an error is returned.
+	// The variable i makes it such that the ith call to failWriter.Write will
+	// return errIO. Since failWriter errors are not persistent, we must ensure
+	// that flate.Writer errors are persistent.
+	for i := 0; i < 1000; i++ {
+		fw := &failWriter{i}
+		zw.Reset(fw)
+
+		_, werr := zw.Write(d)
+		cerr := zw.Close()
+		if werr != errIO && werr != nil {
+			t.Errorf("test %d, mismatching Write error: got %v, want %v", i, werr, errIO)
+		}
+		if cerr != errIO && fw.n < 0 {
+			t.Errorf("test %d, mismatching Close error: got %v, want %v", i, cerr, errIO)
+		}
+		if fw.n >= 0 {
+			// At this point, the failure threshold was sufficiently high enough
+			// that we wrote the whole stream without any errors.
+			return
+		}
+	}
+}
+
+func TestBestSpeedMatch(t *testing.T) {
+	t.Parallel()
+	cases := []struct {
+		previous, current []byte
+		t, s, want        int32
+	}{{
+		previous: []byte{0, 0, 0, 1, 2},
+		current:  []byte{3, 4, 5, 0, 1, 2, 3, 4, 5},
+		t:        -3,
+		s:        3,
+		want:     6,
+	}, {
+		previous: []byte{0, 0, 0, 1, 2},
+		current:  []byte{2, 4, 5, 0, 1, 2, 3, 4, 5},
+		t:        -3,
+		s:        3,
+		want:     3,
+	}, {
+		previous: []byte{0, 0, 0, 1, 1},
+		current:  []byte{3, 4, 5, 0, 1, 2, 3, 4, 5},
+		t:        -3,
+		s:        3,
+		want:     2,
+	}, {
+		previous: []byte{0, 0, 0, 1, 2},
+		current:  []byte{2, 2, 2, 2, 1, 2, 3, 4, 5},
+		t:        -1,
+		s:        0,
+		want:     4,
+	}, {
+		previous: []byte{0, 0, 0, 1, 2, 3, 4, 5, 2, 2},
+		current:  []byte{2, 2, 2, 2, 1, 2, 3, 4, 5},
+		t:        -7,
+		s:        4,
+		want:     5,
+	}, {
+		previous: []byte{9, 9, 9, 9, 9},
+		current:  []byte{2, 2, 2, 2, 1, 2, 3, 4, 5},
+		t:        -1,
+		s:        0,
+		want:     0,
+	}, {
+		previous: []byte{9, 9, 9, 9, 9},
+		current:  []byte{9, 2, 2, 2, 1, 2, 3, 4, 5},
+		t:        0,
+		s:        1,
+		want:     0,
+	}, {
+		previous: []byte{},
+		current:  []byte{9, 2, 2, 2, 1, 2, 3, 4, 5},
+		t:        -5,
+		s:        1,
+		want:     0,
+	}, {
+		previous: []byte{},
+		current:  []byte{9, 2, 2, 2, 1, 2, 3, 4, 5},
+		t:        -1,
+		s:        1,
+		want:     0,
+	}, {
+		previous: []byte{},
+		current:  []byte{2, 2, 2, 2, 1, 2, 3, 4, 5},
+		t:        0,
+		s:        1,
+		want:     3,
+	}, {
+		previous: []byte{3, 4, 5},
+		current:  []byte{3, 4, 5},
+		t:        -3,
+		s:        0,
+		want:     3,
+	}, {
+		previous: make([]byte, 1000),
+		current:  make([]byte, 1000),
+		t:        -1000,
+		s:        0,
+		want:     maxMatchLength - 4,
+	}, {
+		previous: make([]byte, 200),
+		current:  make([]byte, 500),
+		t:        -200,
+		s:        0,
+		want:     maxMatchLength - 4,
+	}, {
+		previous: make([]byte, 200),
+		current:  make([]byte, 500),
+		t:        0,
+		s:        1,
+		want:     maxMatchLength - 4,
+	}, {
+		previous: make([]byte, maxMatchLength-4),
+		current:  make([]byte, 500),
+		t:        -(maxMatchLength - 4),
+		s:        0,
+		want:     maxMatchLength - 4,
+	}, {
+		previous: make([]byte, 200),
+		current:  make([]byte, 500),
+		t:        -200,
+		s:        400,
+		want:     100,
+	}, {
+		previous: make([]byte, 10),
+		current:  make([]byte, 500),
+		t:        200,
+		s:        400,
+		want:     100,
+	}}
+	for i, c := range cases {
+		e := deflateFast{prev: c.previous}
+		got := e.matchLen(c.s, c.t, c.current)
+		if got != c.want {
+			t.Errorf("Test %d: match length, want %d, got %d", i, c.want, got)
+		}
+	}
+}
+
+func TestBestSpeedMaxMatchOffset(t *testing.T) {
+	t.Parallel()
+	const abc, xyz = "abcdefgh", "stuvwxyz"
+	for _, matchBefore := range []bool{false, true} {
+		for _, extra := range []int{0, inputMargin - 1, inputMargin, inputMargin + 1, 2 * inputMargin} {
+			for offsetAdj := -5; offsetAdj <= +5; offsetAdj++ {
+				report := func(desc string, err error) {
+					t.Errorf("matchBefore=%t, extra=%d, offsetAdj=%d: %s%v",
+						matchBefore, extra, offsetAdj, desc, err)
+				}
+
+				offset := maxMatchOffset + offsetAdj
+
+				// Make src to be a []byte of the form
+				//	"%s%s%s%s%s" % (abc, zeros0, xyzMaybe, abc, zeros1)
+				// where:
+				//	zeros0 is approximately maxMatchOffset zeros.
+				//	xyzMaybe is either xyz or the empty string.
+				//	zeros1 is between 0 and 30 zeros.
+				// The difference between the two abc's will be offset, which
+				// is maxMatchOffset plus or minus a small adjustment.
+				src := make([]byte, offset+len(abc)+extra)
+				copy(src, abc)
+				if !matchBefore {
+					copy(src[offset-len(xyz):], xyz)
+				}
+				copy(src[offset:], abc)
+
+				buf := new(bytes.Buffer)
+				w, err := NewWriter(buf, BestSpeed)
+				if err != nil {
+					report("NewWriter: ", err)
+					continue
+				}
+				if _, err := w.Write(src); err != nil {
+					report("Write: ", err)
+					continue
+				}
+				if err := w.Close(); err != nil {
+					report("Writer.Close: ", err)
+					continue
+				}
+
+				r := NewReader(buf)
+				dst, err := io.ReadAll(r)
+				r.Close()
+				if err != nil {
+					report("ReadAll: ", err)
+					continue
+				}
+
+				if !bytes.Equal(dst, src) {
+					report("", fmt.Errorf("bytes differ after round-tripping"))
+					continue
+				}
+			}
+		}
+	}
+}
+
+func TestBestSpeedShiftOffsets(t *testing.T) {
+	// Test if shiftoffsets properly preserves matches and resets out-of-range matches
+	// seen in https://github.com/golang/go/issues/4142
+	enc := newDeflateFast()
+
+	// testData may not generate internal matches.
+	testData := make([]byte, 32)
+	rng := rand.New(rand.NewSource(0))
+	for i := range testData {
+		testData[i] = byte(rng.Uint32())
+	}
+
+	// Encode the testdata with clean state.
+	// Second part should pick up matches from the first block.
+	wantFirstTokens := len(enc.encode(nil, testData))
+	wantSecondTokens := len(enc.encode(nil, testData))
+
+	if wantFirstTokens <= wantSecondTokens {
+		t.Fatalf("test needs matches between inputs to be generated")
+	}
+	// Forward the current indicator to before wraparound.
+	enc.cur = bufferReset - int32(len(testData))
+
+	// Part 1 before wrap, should match clean state.
+	got := len(enc.encode(nil, testData))
+	if wantFirstTokens != got {
+		t.Errorf("got %d, want %d tokens", got, wantFirstTokens)
+	}
+
+	// Verify we are about to wrap.
+	if enc.cur != bufferReset {
+		t.Errorf("got %d, want e.cur to be at bufferReset (%d)", enc.cur, bufferReset)
+	}
+
+	// Part 2 should match clean state as well even if wrapped.
+	got = len(enc.encode(nil, testData))
+	if wantSecondTokens != got {
+		t.Errorf("got %d, want %d token", got, wantSecondTokens)
+	}
+
+	// Verify that we wrapped.
+	if enc.cur >= bufferReset {
+		t.Errorf("want e.cur to be < bufferReset (%d), got %d", bufferReset, enc.cur)
+	}
+
+	// Forward the current buffer, leaving the matches at the bottom.
+	enc.cur = bufferReset
+	enc.shiftOffsets()
+
+	// Ensure that no matches were picked up.
+	got = len(enc.encode(nil, testData))
+	if wantFirstTokens != got {
+		t.Errorf("got %d, want %d tokens", got, wantFirstTokens)
+	}
+}
+
+func TestMaxStackSize(t *testing.T) {
+	// This test must not run in parallel with other tests as debug.SetMaxStack
+	// affects all goroutines.
+	n := debug.SetMaxStack(1 << 16)
+	defer debug.SetMaxStack(n)
+
+	var wg sync.WaitGroup
+	defer wg.Wait()
+
+	b := make([]byte, 1<<20)
+	for level := HuffmanOnly; level <= BestCompression; level++ {
+		// Run in separate goroutine to increase probability of stack regrowth.
+		wg.Add(1)
+		go func(level int) {
+			defer wg.Done()
+			zw, err := NewWriter(io.Discard, level)
+			if err != nil {
+				t.Errorf("level %d, NewWriter() = %v, want nil", level, err)
+			}
+			if n, err := zw.Write(b); n != len(b) || err != nil {
+				t.Errorf("level %d, Write() = (%d, %v), want (%d, nil)", level, n, err, len(b))
+			}
+			if err := zw.Close(); err != nil {
+				t.Errorf("level %d, Close() = %v, want nil", level, err)
+			}
+			zw.Reset(io.Discard)
+		}(level)
+	}
+}
diff --git a/src/compress/flate/deflatefast.go b/src/compress/flate/deflatefast.go
new file mode 100644
index 0000000..6aa439f
--- /dev/null
+++ b/src/compress/flate/deflatefast.go
@@ -0,0 +1,309 @@
+// Copyright 2016 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package flate
+
+import "math"
+
+// This encoding algorithm, which prioritizes speed over output size, is
+// based on Snappy's LZ77-style encoder: github.com/golang/snappy
+
+const (
+	tableBits  = 14             // Bits used in the table.
+	tableSize  = 1 << tableBits // Size of the table.
+	tableMask  = tableSize - 1  // Mask for table indices. Redundant, but can eliminate bounds checks.
+	tableShift = 32 - tableBits // Right-shift to get the tableBits most significant bits of a uint32.
+
+	// Reset the buffer offset when reaching this.
+	// Offsets are stored between blocks as int32 values.
+	// Since the offset we are checking against is at the beginning
+	// of the buffer, we need to subtract the current and input
+	// buffer to not risk overflowing the int32.
+	bufferReset = math.MaxInt32 - maxStoreBlockSize*2
+)
+
+func load32(b []byte, i int32) uint32 {
+	b = b[i : i+4 : len(b)] // Help the compiler eliminate bounds checks on the next line.
+	return uint32(b[0]) | uint32(b[1])<<8 | uint32(b[2])<<16 | uint32(b[3])<<24
+}
+
+func load64(b []byte, i int32) uint64 {
+	b = b[i : i+8 : len(b)] // Help the compiler eliminate bounds checks on the next line.
+	return uint64(b[0]) | uint64(b[1])<<8 | uint64(b[2])<<16 | uint64(b[3])<<24 |
+		uint64(b[4])<<32 | uint64(b[5])<<40 | uint64(b[6])<<48 | uint64(b[7])<<56
+}
+
+func hash(u uint32) uint32 {
+	return (u * 0x1e35a7bd) >> tableShift
+}
+
+// These constants are defined by the Snappy implementation so that its
+// assembly implementation can fast-path some 16-bytes-at-a-time copies. They
+// aren't necessary in the pure Go implementation, as we don't use those same
+// optimizations, but using the same thresholds doesn't really hurt.
+const (
+	inputMargin            = 16 - 1
+	minNonLiteralBlockSize = 1 + 1 + inputMargin
+)
+
+type tableEntry struct {
+	val    uint32 // Value at destination
+	offset int32
+}
+
+// deflateFast maintains the table for matches,
+// and the previous byte block for cross block matching.
+type deflateFast struct {
+	table [tableSize]tableEntry
+	prev  []byte // Previous block, zero length if unknown.
+	cur   int32  // Current match offset.
+}
+
+func newDeflateFast() *deflateFast {
+	return &deflateFast{cur: maxStoreBlockSize, prev: make([]byte, 0, maxStoreBlockSize)}
+}
+
+// encode encodes a block given in src and appends tokens
+// to dst and returns the result.
+func (e *deflateFast) encode(dst []token, src []byte) []token {
+	// Ensure that e.cur doesn't wrap.
+	if e.cur >= bufferReset {
+		e.shiftOffsets()
+	}
+
+	// This check isn't in the Snappy implementation, but there, the caller
+	// instead of the callee handles this case.
+	if len(src) < minNonLiteralBlockSize {
+		e.cur += maxStoreBlockSize
+		e.prev = e.prev[:0]
+		return emitLiteral(dst, src)
+	}
+
+	// sLimit is when to stop looking for offset/length copies. The inputMargin
+	// lets us use a fast path for emitLiteral in the main loop, while we are
+	// looking for copies.
+	sLimit := int32(len(src) - inputMargin)
+
+	// nextEmit is where in src the next emitLiteral should start from.
+	nextEmit := int32(0)
+	s := int32(0)
+	cv := load32(src, s)
+	nextHash := hash(cv)
+
+	for {
+		// Copied from the C++ snappy implementation:
+		//
+		// Heuristic match skipping: If 32 bytes are scanned with no matches
+		// found, start looking only at every other byte. If 32 more bytes are
+		// scanned (or skipped), look at every third byte, etc.. When a match
+		// is found, immediately go back to looking at every byte. This is a
+		// small loss (~5% performance, ~0.1% density) for compressible data
+		// due to more bookkeeping, but for non-compressible data (such as
+		// JPEG) it's a huge win since the compressor quickly "realizes" the
+		// data is incompressible and doesn't bother looking for matches
+		// everywhere.
+		//
+		// The "skip" variable keeps track of how many bytes there are since
+		// the last match; dividing it by 32 (ie. right-shifting by five) gives
+		// the number of bytes to move ahead for each iteration.
+		skip := int32(32)
+
+		nextS := s
+		var candidate tableEntry
+		for {
+			s = nextS
+			bytesBetweenHashLookups := skip >> 5
+			nextS = s + bytesBetweenHashLookups
+			skip += bytesBetweenHashLookups
+			if nextS > sLimit {
+				goto emitRemainder
+			}
+			candidate = e.table[nextHash&tableMask]
+			now := load32(src, nextS)
+			e.table[nextHash&tableMask] = tableEntry{offset: s + e.cur, val: cv}
+			nextHash = hash(now)
+
+			offset := s - (candidate.offset - e.cur)
+			if offset > maxMatchOffset || cv != candidate.val {
+				// Out of range or not matched.
+				cv = now
+				continue
+			}
+			break
+		}
+
+		// A 4-byte match has been found. We'll later see if more than 4 bytes
+		// match. But, prior to the match, src[nextEmit:s] are unmatched. Emit
+		// them as literal bytes.
+		dst = emitLiteral(dst, src[nextEmit:s])
+
+		// Call emitCopy, and then see if another emitCopy could be our next
+		// move. Repeat until we find no match for the input immediately after
+		// what was consumed by the last emitCopy call.
+		//
+		// If we exit this loop normally then we need to call emitLiteral next,
+		// though we don't yet know how big the literal will be. We handle that
+		// by proceeding to the next iteration of the main loop. We also can
+		// exit this loop via goto if we get close to exhausting the input.
+		for {
+			// Invariant: we have a 4-byte match at s, and no need to emit any
+			// literal bytes prior to s.
+
+			// Extend the 4-byte match as long as possible.
+			//
+			s += 4
+			t := candidate.offset - e.cur + 4
+			l := e.matchLen(s, t, src)
+
+			// matchToken is flate's equivalent of Snappy's emitCopy. (length,offset)
+			dst = append(dst, matchToken(uint32(l+4-baseMatchLength), uint32(s-t-baseMatchOffset)))
+			s += l
+			nextEmit = s
+			if s >= sLimit {
+				goto emitRemainder
+			}
+
+			// We could immediately start working at s now, but to improve
+			// compression we first update the hash table at s-1 and at s. If
+			// another emitCopy is not our next move, also calculate nextHash
+			// at s+1. At least on GOARCH=amd64, these three hash calculations
+			// are faster as one load64 call (with some shifts) instead of
+			// three load32 calls.
+			x := load64(src, s-1)
+			prevHash := hash(uint32(x))
+			e.table[prevHash&tableMask] = tableEntry{offset: e.cur + s - 1, val: uint32(x)}
+			x >>= 8
+			currHash := hash(uint32(x))
+			candidate = e.table[currHash&tableMask]
+			e.table[currHash&tableMask] = tableEntry{offset: e.cur + s, val: uint32(x)}
+
+			offset := s - (candidate.offset - e.cur)
+			if offset > maxMatchOffset || uint32(x) != candidate.val {
+				cv = uint32(x >> 8)
+				nextHash = hash(cv)
+				s++
+				break
+			}
+		}
+	}
+
+emitRemainder:
+	if int(nextEmit) < len(src) {
+		dst = emitLiteral(dst, src[nextEmit:])
+	}
+	e.cur += int32(len(src))
+	e.prev = e.prev[:len(src)]
+	copy(e.prev, src)
+	return dst
+}
+
+func emitLiteral(dst []token, lit []byte) []token {
+	for _, v := range lit {
+		dst = append(dst, literalToken(uint32(v)))
+	}
+	return dst
+}
+
+// matchLen returns the match length between src[s:] and src[t:].
+// t can be negative to indicate the match is starting in e.prev.
+// We assume that src[s-4:s] and src[t-4:t] already match.
+func (e *deflateFast) matchLen(s, t int32, src []byte) int32 {
+	s1 := int(s) + maxMatchLength - 4
+	if s1 > len(src) {
+		s1 = len(src)
+	}
+
+	// If we are inside the current block
+	if t >= 0 {
+		b := src[t:]
+		a := src[s:s1]
+		b = b[:len(a)]
+		// Extend the match to be as long as possible.
+		for i := range a {
+			if a[i] != b[i] {
+				return int32(i)
+			}
+		}
+		return int32(len(a))
+	}
+
+	// We found a match in the previous block.
+	tp := int32(len(e.prev)) + t
+	if tp < 0 {
+		return 0
+	}
+
+	// Extend the match to be as long as possible.
+	a := src[s:s1]
+	b := e.prev[tp:]
+	if len(b) > len(a) {
+		b = b[:len(a)]
+	}
+	a = a[:len(b)]
+	for i := range b {
+		if a[i] != b[i] {
+			return int32(i)
+		}
+	}
+
+	// If we reached our limit, we matched everything we are
+	// allowed to in the previous block and we return.
+	n := int32(len(b))
+	if int(s+n) == s1 {
+		return n
+	}
+
+	// Continue looking for more matches in the current block.
+	a = src[s+n : s1]
+	b = src[:len(a)]
+	for i := range a {
+		if a[i] != b[i] {
+			return int32(i) + n
+		}
+	}
+	return int32(len(a)) + n
+}
+
+// Reset resets the encoding history.
+// This ensures that no matches are made to the previous block.
+func (e *deflateFast) reset() {
+	e.prev = e.prev[:0]
+	// Bump the offset, so all matches will fail distance check.
+	// Nothing should be >= e.cur in the table.
+	e.cur += maxMatchOffset
+
+	// Protect against e.cur wraparound.
+	if e.cur >= bufferReset {
+		e.shiftOffsets()
+	}
+}
+
+// shiftOffsets will shift down all match offset.
+// This is only called in rare situations to prevent integer overflow.
+//
+// See https://golang.org/issue/18636 and https://github.com/golang/go/issues/34121.
+func (e *deflateFast) shiftOffsets() {
+	if len(e.prev) == 0 {
+		// We have no history; just clear the table.
+		for i := range e.table[:] {
+			e.table[i] = tableEntry{}
+		}
+		e.cur = maxMatchOffset + 1
+		return
+	}
+
+	// Shift down everything in the table that isn't already too far away.
+	for i := range e.table[:] {
+		v := e.table[i].offset - e.cur + maxMatchOffset + 1
+		if v < 0 {
+			// We want to reset e.cur to maxMatchOffset + 1, so we need to shift
+			// all table entries down by (e.cur - (maxMatchOffset + 1)).
+			// Because we ignore matches > maxMatchOffset, we can cap
+			// any negative offsets at 0.
+			v = 0
+		}
+		e.table[i].offset = v
+	}
+	e.cur = maxMatchOffset + 1
+}
diff --git a/src/compress/flate/dict_decoder.go b/src/compress/flate/dict_decoder.go
new file mode 100644
index 0000000..3b59d48
--- /dev/null
+++ b/src/compress/flate/dict_decoder.go
@@ -0,0 +1,182 @@
+// Copyright 2016 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package flate
+
+// dictDecoder implements the LZ77 sliding dictionary as used in decompression.
+// LZ77 decompresses data through sequences of two forms of commands:
+//
+//	* Literal insertions: Runs of one or more symbols are inserted into the data
+//	stream as is. This is accomplished through the writeByte method for a
+//	single symbol, or combinations of writeSlice/writeMark for multiple symbols.
+//	Any valid stream must start with a literal insertion if no preset dictionary
+//	is used.
+//
+//	* Backward copies: Runs of one or more symbols are copied from previously
+//	emitted data. Backward copies come as the tuple (dist, length) where dist
+//	determines how far back in the stream to copy from and length determines how
+//	many bytes to copy. Note that it is valid for the length to be greater than
+//	the distance. Since LZ77 uses forward copies, that situation is used to
+//	perform a form of run-length encoding on repeated runs of symbols.
+//	The writeCopy and tryWriteCopy are used to implement this command.
+//
+// For performance reasons, this implementation performs little to no sanity
+// checks about the arguments. As such, the invariants documented for each
+// method call must be respected.
+type dictDecoder struct {
+	hist []byte // Sliding window history
+
+	// Invariant: 0 <= rdPos <= wrPos <= len(hist)
+	wrPos int  // Current output position in buffer
+	rdPos int  // Have emitted hist[:rdPos] already
+	full  bool // Has a full window length been written yet?
+}
+
+// init initializes dictDecoder to have a sliding window dictionary of the given
+// size. If a preset dict is provided, it will initialize the dictionary with
+// the contents of dict.
+func (dd *dictDecoder) init(size int, dict []byte) {
+	*dd = dictDecoder{hist: dd.hist}
+
+	if cap(dd.hist) < size {
+		dd.hist = make([]byte, size)
+	}
+	dd.hist = dd.hist[:size]
+
+	if len(dict) > len(dd.hist) {
+		dict = dict[len(dict)-len(dd.hist):]
+	}
+	dd.wrPos = copy(dd.hist, dict)
+	if dd.wrPos == len(dd.hist) {
+		dd.wrPos = 0
+		dd.full = true
+	}
+	dd.rdPos = dd.wrPos
+}
+
+// histSize reports the total amount of historical data in the dictionary.
+func (dd *dictDecoder) histSize() int {
+	if dd.full {
+		return len(dd.hist)
+	}
+	return dd.wrPos
+}
+
+// availRead reports the number of bytes that can be flushed by readFlush.
+func (dd *dictDecoder) availRead() int {
+	return dd.wrPos - dd.rdPos
+}
+
+// availWrite reports the available amount of output buffer space.
+func (dd *dictDecoder) availWrite() int {
+	return len(dd.hist) - dd.wrPos
+}
+
+// writeSlice returns a slice of the available buffer to write data to.
+//
+// This invariant will be kept: len(s) <= availWrite()
+func (dd *dictDecoder) writeSlice() []byte {
+	return dd.hist[dd.wrPos:]
+}
+
+// writeMark advances the writer pointer by cnt.
+//
+// This invariant must be kept: 0 <= cnt <= availWrite()
+func (dd *dictDecoder) writeMark(cnt int) {
+	dd.wrPos += cnt
+}
+
+// writeByte writes a single byte to the dictionary.
+//
+// This invariant must be kept: 0 < availWrite()
+func (dd *dictDecoder) writeByte(c byte) {
+	dd.hist[dd.wrPos] = c
+	dd.wrPos++
+}
+
+// writeCopy copies a string at a given (dist, length) to the output.
+// This returns the number of bytes copied and may be less than the requested
+// length if the available space in the output buffer is too small.
+//
+// This invariant must be kept: 0 < dist <= histSize()
+func (dd *dictDecoder) writeCopy(dist, length int) int {
+	dstBase := dd.wrPos
+	dstPos := dstBase
+	srcPos := dstPos - dist
+	endPos := dstPos + length
+	if endPos > len(dd.hist) {
+		endPos = len(dd.hist)
+	}
+
+	// Copy non-overlapping section after destination position.
+	//
+	// This section is non-overlapping in that the copy length for this section
+	// is always less than or equal to the backwards distance. This can occur
+	// if a distance refers to data that wraps-around in the buffer.
+	// Thus, a backwards copy is performed here; that is, the exact bytes in
+	// the source prior to the copy is placed in the destination.
+	if srcPos < 0 {
+		srcPos += len(dd.hist)
+		dstPos += copy(dd.hist[dstPos:endPos], dd.hist[srcPos:])
+		srcPos = 0
+	}
+
+	// Copy possibly overlapping section before destination position.
+	//
+	// This section can overlap if the copy length for this section is larger
+	// than the backwards distance. This is allowed by LZ77 so that repeated
+	// strings can be succinctly represented using (dist, length) pairs.
+	// Thus, a forwards copy is performed here; that is, the bytes copied is
+	// possibly dependent on the resulting bytes in the destination as the copy
+	// progresses along. This is functionally equivalent to the following:
+	//
+	//	for i := 0; i < endPos-dstPos; i++ {
+	//		dd.hist[dstPos+i] = dd.hist[srcPos+i]
+	//	}
+	//	dstPos = endPos
+	//
+	for dstPos < endPos {
+		dstPos += copy(dd.hist[dstPos:endPos], dd.hist[srcPos:dstPos])
+	}
+
+	dd.wrPos = dstPos
+	return dstPos - dstBase
+}
+
+// tryWriteCopy tries to copy a string at a given (distance, length) to the
+// output. This specialized version is optimized for short distances.
+//
+// This method is designed to be inlined for performance reasons.
+//
+// This invariant must be kept: 0 < dist <= histSize()
+func (dd *dictDecoder) tryWriteCopy(dist, length int) int {
+	dstPos := dd.wrPos
+	endPos := dstPos + length
+	if dstPos < dist || endPos > len(dd.hist) {
+		return 0
+	}
+	dstBase := dstPos
+	srcPos := dstPos - dist
+
+	// Copy possibly overlapping section before destination position.
+	for dstPos < endPos {
+		dstPos += copy(dd.hist[dstPos:endPos], dd.hist[srcPos:dstPos])
+	}
+
+	dd.wrPos = dstPos
+	return dstPos - dstBase
+}
+
+// readFlush returns a slice of the historical buffer that is ready to be
+// emitted to the user. The data returned by readFlush must be fully consumed
+// before calling any other dictDecoder methods.
+func (dd *dictDecoder) readFlush() []byte {
+	toRead := dd.hist[dd.rdPos:dd.wrPos]
+	dd.rdPos = dd.wrPos
+	if dd.wrPos == len(dd.hist) {
+		dd.wrPos, dd.rdPos = 0, 0
+		dd.full = true
+	}
+	return toRead
+}
diff --git a/src/compress/flate/dict_decoder_test.go b/src/compress/flate/dict_decoder_test.go
new file mode 100644
index 0000000..9275cff
--- /dev/null
+++ b/src/compress/flate/dict_decoder_test.go
@@ -0,0 +1,139 @@
+// Copyright 2016 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package flate
+
+import (
+	"bytes"
+	"strings"
+	"testing"
+)
+
+func TestDictDecoder(t *testing.T) {
+	const (
+		abc  = "ABC\n"
+		fox  = "The quick brown fox jumped over the lazy dog!\n"
+		poem = "The Road Not Taken\nRobert Frost\n" +
+			"\n" +
+			"Two roads diverged in a yellow wood,\n" +
+			"And sorry I could not travel both\n" +
+			"And be one traveler, long I stood\n" +
+			"And looked down one as far as I could\n" +
+			"To where it bent in the undergrowth;\n" +
+			"\n" +
+			"Then took the other, as just as fair,\n" +
+			"And having perhaps the better claim,\n" +
+			"Because it was grassy and wanted wear;\n" +
+			"Though as for that the passing there\n" +
+			"Had worn them really about the same,\n" +
+			"\n" +
+			"And both that morning equally lay\n" +
+			"In leaves no step had trodden black.\n" +
+			"Oh, I kept the first for another day!\n" +
+			"Yet knowing how way leads on to way,\n" +
+			"I doubted if I should ever come back.\n" +
+			"\n" +
+			"I shall be telling this with a sigh\n" +
+			"Somewhere ages and ages hence:\n" +
+			"Two roads diverged in a wood, and I-\n" +
+			"I took the one less traveled by,\n" +
+			"And that has made all the difference.\n"
+	)
+
+	var poemRefs = []struct {
+		dist   int // Backward distance (0 if this is an insertion)
+		length int // Length of copy or insertion
+	}{
+		{0, 38}, {33, 3}, {0, 48}, {79, 3}, {0, 11}, {34, 5}, {0, 6}, {23, 7},
+		{0, 8}, {50, 3}, {0, 2}, {69, 3}, {34, 5}, {0, 4}, {97, 3}, {0, 4},
+		{43, 5}, {0, 6}, {7, 4}, {88, 7}, {0, 12}, {80, 3}, {0, 2}, {141, 4},
+		{0, 1}, {196, 3}, {0, 3}, {157, 3}, {0, 6}, {181, 3}, {0, 2}, {23, 3},
+		{77, 3}, {28, 5}, {128, 3}, {110, 4}, {70, 3}, {0, 4}, {85, 6}, {0, 2},
+		{182, 6}, {0, 4}, {133, 3}, {0, 7}, {47, 5}, {0, 20}, {112, 5}, {0, 1},
+		{58, 3}, {0, 8}, {59, 3}, {0, 4}, {173, 3}, {0, 5}, {114, 3}, {0, 4},
+		{92, 5}, {0, 2}, {71, 3}, {0, 2}, {76, 5}, {0, 1}, {46, 3}, {96, 4},
+		{130, 4}, {0, 3}, {360, 3}, {0, 3}, {178, 5}, {0, 7}, {75, 3}, {0, 3},
+		{45, 6}, {0, 6}, {299, 6}, {180, 3}, {70, 6}, {0, 1}, {48, 3}, {66, 4},
+		{0, 3}, {47, 5}, {0, 9}, {325, 3}, {0, 1}, {359, 3}, {318, 3}, {0, 2},
+		{199, 3}, {0, 1}, {344, 3}, {0, 3}, {248, 3}, {0, 10}, {310, 3}, {0, 3},
+		{93, 6}, {0, 3}, {252, 3}, {157, 4}, {0, 2}, {273, 5}, {0, 14}, {99, 4},
+		{0, 1}, {464, 4}, {0, 2}, {92, 4}, {495, 3}, {0, 1}, {322, 4}, {16, 4},
+		{0, 3}, {402, 3}, {0, 2}, {237, 4}, {0, 2}, {432, 4}, {0, 1}, {483, 5},
+		{0, 2}, {294, 4}, {0, 2}, {306, 3}, {113, 5}, {0, 1}, {26, 4}, {164, 3},
+		{488, 4}, {0, 1}, {542, 3}, {248, 6}, {0, 5}, {205, 3}, {0, 8}, {48, 3},
+		{449, 6}, {0, 2}, {192, 3}, {328, 4}, {9, 5}, {433, 3}, {0, 3}, {622, 25},
+		{615, 5}, {46, 5}, {0, 2}, {104, 3}, {475, 10}, {549, 3}, {0, 4}, {597, 8},
+		{314, 3}, {0, 1}, {473, 6}, {317, 5}, {0, 1}, {400, 3}, {0, 3}, {109, 3},
+		{151, 3}, {48, 4}, {0, 4}, {125, 3}, {108, 3}, {0, 2},
+	}
+
+	var got, want bytes.Buffer
+	var dd dictDecoder
+	dd.init(1<<11, nil)
+
+	var writeCopy = func(dist, length int) {
+		for length > 0 {
+			cnt := dd.tryWriteCopy(dist, length)
+			if cnt == 0 {
+				cnt = dd.writeCopy(dist, length)
+			}
+
+			length -= cnt
+			if dd.availWrite() == 0 {
+				got.Write(dd.readFlush())
+			}
+		}
+	}
+	var writeString = func(str string) {
+		for len(str) > 0 {
+			cnt := copy(dd.writeSlice(), str)
+			str = str[cnt:]
+			dd.writeMark(cnt)
+			if dd.availWrite() == 0 {
+				got.Write(dd.readFlush())
+			}
+		}
+	}
+
+	writeString(".")
+	want.WriteByte('.')
+
+	str := poem
+	for _, ref := range poemRefs {
+		if ref.dist == 0 {
+			writeString(str[:ref.length])
+		} else {
+			writeCopy(ref.dist, ref.length)
+		}
+		str = str[ref.length:]
+	}
+	want.WriteString(poem)
+
+	writeCopy(dd.histSize(), 33)
+	want.Write(want.Bytes()[:33])
+
+	writeString(abc)
+	writeCopy(len(abc), 59*len(abc))
+	want.WriteString(strings.Repeat(abc, 60))
+
+	writeString(fox)
+	writeCopy(len(fox), 9*len(fox))
+	want.WriteString(strings.Repeat(fox, 10))
+
+	writeString(".")
+	writeCopy(1, 9)
+	want.WriteString(strings.Repeat(".", 10))
+
+	writeString(strings.ToUpper(poem))
+	writeCopy(len(poem), 7*len(poem))
+	want.WriteString(strings.Repeat(strings.ToUpper(poem), 8))
+
+	writeCopy(dd.histSize(), 10)
+	want.Write(want.Bytes()[want.Len()-dd.histSize():][:10])
+
+	got.Write(dd.readFlush())
+	if got.String() != want.String() {
+		t.Errorf("final string mismatch:\ngot  %q\nwant %q", got.String(), want.String())
+	}
+}
diff --git a/src/compress/flate/example_test.go b/src/compress/flate/example_test.go
new file mode 100644
index 0000000..5780092
--- /dev/null
+++ b/src/compress/flate/example_test.go
@@ -0,0 +1,243 @@
+// Copyright 2016 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package flate_test
+
+import (
+	"bytes"
+	"compress/flate"
+	"fmt"
+	"io"
+	"log"
+	"os"
+	"strings"
+	"sync"
+)
+
+// In performance critical applications, Reset can be used to discard the
+// current compressor or decompressor state and reinitialize them quickly
+// by taking advantage of previously allocated memory.
+func Example_reset() {
+	proverbs := []string{
+		"Don't communicate by sharing memory, share memory by communicating.\n",
+		"Concurrency is not parallelism.\n",
+		"The bigger the interface, the weaker the abstraction.\n",
+		"Documentation is for users.\n",
+	}
+
+	var r strings.Reader
+	var b bytes.Buffer
+	buf := make([]byte, 32<<10)
+
+	zw, err := flate.NewWriter(nil, flate.DefaultCompression)
+	if err != nil {
+		log.Fatal(err)
+	}
+	zr := flate.NewReader(nil)
+
+	for _, s := range proverbs {
+		r.Reset(s)
+		b.Reset()
+
+		// Reset the compressor and encode from some input stream.
+		zw.Reset(&b)
+		if _, err := io.CopyBuffer(zw, &r, buf); err != nil {
+			log.Fatal(err)
+		}
+		if err := zw.Close(); err != nil {
+			log.Fatal(err)
+		}
+
+		// Reset the decompressor and decode to some output stream.
+		if err := zr.(flate.Resetter).Reset(&b, nil); err != nil {
+			log.Fatal(err)
+		}
+		if _, err := io.CopyBuffer(os.Stdout, zr, buf); err != nil {
+			log.Fatal(err)
+		}
+		if err := zr.Close(); err != nil {
+			log.Fatal(err)
+		}
+	}
+
+	// Output:
+	// Don't communicate by sharing memory, share memory by communicating.
+	// Concurrency is not parallelism.
+	// The bigger the interface, the weaker the abstraction.
+	// Documentation is for users.
+}
+
+// A preset dictionary can be used to improve the compression ratio.
+// The downside to using a dictionary is that the compressor and decompressor
+// must agree in advance what dictionary to use.
+func Example_dictionary() {
+	// The dictionary is a string of bytes. When compressing some input data,
+	// the compressor will attempt to substitute substrings with matches found
+	// in the dictionary. As such, the dictionary should only contain substrings
+	// that are expected to be found in the actual data stream.
+	const dict = `<?xml version="1.0"?>` + `<book>` + `<data>` + `<meta name="` + `" content="`
+
+	// The data to compress should (but is not required to) contain frequent
+	// substrings that match those in the dictionary.
+	const data = `<?xml version="1.0"?>
+<book>
+	<meta name="title" content="The Go Programming Language"/>
+	<meta name="authors" content="Alan Donovan and Brian Kernighan"/>
+	<meta name="published" content="2015-10-26"/>
+	<meta name="isbn" content="978-0134190440"/>
+	<data>...</data>
+</book>
+`
+
+	var b bytes.Buffer
+
+	// Compress the data using the specially crafted dictionary.
+	zw, err := flate.NewWriterDict(&b, flate.DefaultCompression, []byte(dict))
+	if err != nil {
+		log.Fatal(err)
+	}
+	if _, err := io.Copy(zw, strings.NewReader(data)); err != nil {
+		log.Fatal(err)
+	}
+	if err := zw.Close(); err != nil {
+		log.Fatal(err)
+	}
+
+	// The decompressor must use the same dictionary as the compressor.
+	// Otherwise, the input may appear as corrupted.
+	fmt.Println("Decompressed output using the dictionary:")
+	zr := flate.NewReaderDict(bytes.NewReader(b.Bytes()), []byte(dict))
+	if _, err := io.Copy(os.Stdout, zr); err != nil {
+		log.Fatal(err)
+	}
+	if err := zr.Close(); err != nil {
+		log.Fatal(err)
+	}
+
+	fmt.Println()
+
+	// Substitute all of the bytes in the dictionary with a '#' to visually
+	// demonstrate the approximate effectiveness of using a preset dictionary.
+	fmt.Println("Substrings matched by the dictionary are marked with #:")
+	hashDict := []byte(dict)
+	for i := range hashDict {
+		hashDict[i] = '#'
+	}
+	zr = flate.NewReaderDict(&b, hashDict)
+	if _, err := io.Copy(os.Stdout, zr); err != nil {
+		log.Fatal(err)
+	}
+	if err := zr.Close(); err != nil {
+		log.Fatal(err)
+	}
+
+	// Output:
+	// Decompressed output using the dictionary:
+	// <?xml version="1.0"?>
+	// <book>
+	// 	<meta name="title" content="The Go Programming Language"/>
+	// 	<meta name="authors" content="Alan Donovan and Brian Kernighan"/>
+	// 	<meta name="published" content="2015-10-26"/>
+	// 	<meta name="isbn" content="978-0134190440"/>
+	// 	<data>...</data>
+	// </book>
+	//
+	// Substrings matched by the dictionary are marked with #:
+	// #####################
+	// ######
+	// 	############title###########The Go Programming Language"/#
+	// 	############authors###########Alan Donovan and Brian Kernighan"/#
+	// 	############published###########2015-10-26"/#
+	// 	############isbn###########978-0134190440"/#
+	// 	######...</#####
+	// </#####
+}
+
+// DEFLATE is suitable for transmitting compressed data across the network.
+func Example_synchronization() {
+	var wg sync.WaitGroup
+	defer wg.Wait()
+
+	// Use io.Pipe to simulate a network connection.
+	// A real network application should take care to properly close the
+	// underlying connection.
+	rp, wp := io.Pipe()
+
+	// Start a goroutine to act as the transmitter.
+	wg.Add(1)
+	go func() {
+		defer wg.Done()
+
+		zw, err := flate.NewWriter(wp, flate.BestSpeed)
+		if err != nil {
+			log.Fatal(err)
+		}
+
+		b := make([]byte, 256)
+		for _, m := range strings.Fields("A long time ago in a galaxy far, far away...") {
+			// We use a simple framing format where the first byte is the
+			// message length, followed the message itself.
+			b[0] = uint8(copy(b[1:], m))
+
+			if _, err := zw.Write(b[:1+len(m)]); err != nil {
+				log.Fatal(err)
+			}
+
+			// Flush ensures that the receiver can read all data sent so far.
+			if err := zw.Flush(); err != nil {
+				log.Fatal(err)
+			}
+		}
+
+		if err := zw.Close(); err != nil {
+			log.Fatal(err)
+		}
+	}()
+
+	// Start a goroutine to act as the receiver.
+	wg.Add(1)
+	go func() {
+		defer wg.Done()
+
+		zr := flate.NewReader(rp)
+
+		b := make([]byte, 256)
+		for {
+			// Read the message length.
+			// This is guaranteed to return for every corresponding
+			// Flush and Close on the transmitter side.
+			if _, err := io.ReadFull(zr, b[:1]); err != nil {
+				if err == io.EOF {
+					break // The transmitter closed the stream
+				}
+				log.Fatal(err)
+			}
+
+			// Read the message content.
+			n := int(b[0])
+			if _, err := io.ReadFull(zr, b[:n]); err != nil {
+				log.Fatal(err)
+			}
+
+			fmt.Printf("Received %d bytes: %s\n", n, b[:n])
+		}
+		fmt.Println()
+
+		if err := zr.Close(); err != nil {
+			log.Fatal(err)
+		}
+	}()
+
+	// Output:
+	// Received 1 bytes: A
+	// Received 4 bytes: long
+	// Received 4 bytes: time
+	// Received 3 bytes: ago
+	// Received 2 bytes: in
+	// Received 1 bytes: a
+	// Received 6 bytes: galaxy
+	// Received 4 bytes: far,
+	// Received 3 bytes: far
+	// Received 7 bytes: away...
+}
diff --git a/src/compress/flate/flate_test.go b/src/compress/flate/flate_test.go
new file mode 100644
index 0000000..23f4c47
--- /dev/null
+++ b/src/compress/flate/flate_test.go
@@ -0,0 +1,352 @@
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// This test tests some internals of the flate package.
+// The tests in package compress/gzip serve as the
+// end-to-end test of the decompressor.
+
+package flate
+
+import (
+	"bytes"
+	"encoding/hex"
+	"io"
+	"strings"
+	"testing"
+)
+
+// The following test should not panic.
+func TestIssue5915(t *testing.T) {
+	bits := []int{4, 0, 0, 6, 4, 3, 2, 3, 3, 4, 4, 5, 0, 0, 0, 0, 5, 5, 6,
+		0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 11, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+		0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 7, 8, 6, 0, 11, 0, 8, 0, 6, 6, 10, 8}
+	var h huffmanDecoder
+	if h.init(bits) {
+		t.Fatalf("Given sequence of bits is bad, and should not succeed.")
+	}
+}
+
+// The following test should not panic.
+func TestIssue5962(t *testing.T) {
+	bits := []int{4, 0, 0, 6, 4, 3, 2, 3, 3, 4, 4, 5, 0, 0, 0, 0,
+		5, 5, 6, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 11}
+	var h huffmanDecoder
+	if h.init(bits) {
+		t.Fatalf("Given sequence of bits is bad, and should not succeed.")
+	}
+}
+
+// The following test should not panic.
+func TestIssue6255(t *testing.T) {
+	bits1 := []int{1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 11}
+	bits2 := []int{11, 13}
+	var h huffmanDecoder
+	if !h.init(bits1) {
+		t.Fatalf("Given sequence of bits is good and should succeed.")
+	}
+	if h.init(bits2) {
+		t.Fatalf("Given sequence of bits is bad and should not succeed.")
+	}
+}
+
+func TestInvalidEncoding(t *testing.T) {
+	// Initialize Huffman decoder to recognize "0".
+	var h huffmanDecoder
+	if !h.init([]int{1}) {
+		t.Fatal("Failed to initialize Huffman decoder")
+	}
+
+	// Initialize decompressor with invalid Huffman coding.
+	var f decompressor
+	f.r = bytes.NewReader([]byte{0xff})
+
+	_, err := f.huffSym(&h)
+	if err == nil {
+		t.Fatal("Should have rejected invalid bit sequence")
+	}
+}
+
+func TestInvalidBits(t *testing.T) {
+	oversubscribed := []int{1, 2, 3, 4, 4, 5}
+	incomplete := []int{1, 2, 4, 4}
+	var h huffmanDecoder
+	if h.init(oversubscribed) {
+		t.Fatal("Should reject oversubscribed bit-length set")
+	}
+	if h.init(incomplete) {
+		t.Fatal("Should reject incomplete bit-length set")
+	}
+}
+
+func TestStreams(t *testing.T) {
+	// To verify any of these hexstrings as valid or invalid flate streams
+	// according to the C zlib library, you can use the Python wrapper library:
+	// >>> hex_string = "010100feff11"
+	// >>> import zlib
+	// >>> zlib.decompress(hex_string.decode("hex"), -15) # Negative means raw DEFLATE
+	// '\x11'
+
+	testCases := []struct {
+		desc   string // Description of the stream
+		stream string // Hexstring of the input DEFLATE stream
+		want   string // Expected result. Use "fail" to expect failure
+	}{{
+		"degenerate HCLenTree",
+		"05e0010000000000100000000000000000000000000000000000000000000000" +
+			"00000000000000000004",
+		"fail",
+	}, {
+		"complete HCLenTree, empty HLitTree, empty HDistTree",
+		"05e0010400000000000000000000000000000000000000000000000000000000" +
+			"00000000000000000010",
+		"fail",
+	}, {
+		"empty HCLenTree",
+		"05e0010000000000000000000000000000000000000000000000000000000000" +
+			"00000000000000000010",
+		"fail",
+	}, {
+		"complete HCLenTree, complete HLitTree, empty HDistTree, use missing HDist symbol",
+		"000100feff000de0010400000000100000000000000000000000000000000000" +
+			"0000000000000000000000000000002c",
+		"fail",
+	}, {
+		"complete HCLenTree, complete HLitTree, degenerate HDistTree, use missing HDist symbol",
+		"000100feff000de0010000000000000000000000000000000000000000000000" +
+			"00000000000000000610000000004070",
+		"fail",
+	}, {
+		"complete HCLenTree, empty HLitTree, empty HDistTree",
+		"05e0010400000000100400000000000000000000000000000000000000000000" +
+			"0000000000000000000000000008",
+		"fail",
+	}, {
+		"complete HCLenTree, empty HLitTree, degenerate HDistTree",
+		"05e0010400000000100400000000000000000000000000000000000000000000" +
+			"0000000000000000000800000008",
+		"fail",
+	}, {
+		"complete HCLenTree, degenerate HLitTree, degenerate HDistTree, use missing HLit symbol",
+		"05e0010400000000100000000000000000000000000000000000000000000000" +
+			"0000000000000000001c",
+		"fail",
+	}, {
+		"complete HCLenTree, complete HLitTree, too large HDistTree",
+		"edff870500000000200400000000000000000000000000000000000000000000" +
+			"000000000000000000080000000000000004",
+		"fail",
+	}, {
+		"complete HCLenTree, complete HLitTree, empty HDistTree, excessive repeater code",
+		"edfd870500000000200400000000000000000000000000000000000000000000" +
+			"000000000000000000e8b100",
+		"fail",
+	}, {
+		"complete HCLenTree, complete HLitTree, empty HDistTree of normal length 30",
+		"05fd01240000000000f8ffffffffffffffffffffffffffffffffffffffffffff" +
+			"ffffffffffffffffff07000000fe01",
+		"",
+	}, {
+		"complete HCLenTree, complete HLitTree, empty HDistTree of excessive length 31",
+		"05fe01240000000000f8ffffffffffffffffffffffffffffffffffffffffffff" +
+			"ffffffffffffffffff07000000fc03",
+		"fail",
+	}, {
+		"complete HCLenTree, over-subscribed HLitTree, empty HDistTree",
+		"05e001240000000000fcffffffffffffffffffffffffffffffffffffffffffff" +
+			"ffffffffffffffffff07f00f",
+		"fail",
+	}, {
+		"complete HCLenTree, under-subscribed HLitTree, empty HDistTree",
+		"05e001240000000000fcffffffffffffffffffffffffffffffffffffffffffff" +
+			"fffffffffcffffffff07f00f",
+		"fail",
+	}, {
+		"complete HCLenTree, complete HLitTree with single code, empty HDistTree",
+		"05e001240000000000f8ffffffffffffffffffffffffffffffffffffffffffff" +
+			"ffffffffffffffffff07f00f",
+		"01",
+	}, {
+		"complete HCLenTree, complete HLitTree with multiple codes, empty HDistTree",
+		"05e301240000000000f8ffffffffffffffffffffffffffffffffffffffffffff" +
+			"ffffffffffffffffff07807f",
+		"01",
+	}, {
+		"complete HCLenTree, complete HLitTree, degenerate HDistTree, use valid HDist symbol",
+		"000100feff000de0010400000000100000000000000000000000000000000000" +
+			"0000000000000000000000000000003c",
+		"00000000",
+	}, {
+		"complete HCLenTree, degenerate HLitTree, degenerate HDistTree",
+		"05e0010400000000100000000000000000000000000000000000000000000000" +
+			"0000000000000000000c",
+		"",
+	}, {
+		"complete HCLenTree, degenerate HLitTree, empty HDistTree",
+		"05e0010400000000100000000000000000000000000000000000000000000000" +
+			"00000000000000000004",
+		"",
+	}, {
+		"complete HCLenTree, complete HLitTree, empty HDistTree, spanning repeater code",
+		"edfd870500000000200400000000000000000000000000000000000000000000" +
+			"000000000000000000e8b000",
+		"",
+	}, {
+		"complete HCLenTree with length codes, complete HLitTree, empty HDistTree",
+		"ede0010400000000100000000000000000000000000000000000000000000000" +
+			"0000000000000000000400004000",
+		"",
+	}, {
+		"complete HCLenTree, complete HLitTree, degenerate HDistTree, use valid HLit symbol 284 with count 31",
+		"000100feff00ede0010400000000100000000000000000000000000000000000" +
+			"000000000000000000000000000000040000407f00",
+		"0000000000000000000000000000000000000000000000000000000000000000" +
+			"0000000000000000000000000000000000000000000000000000000000000000" +
+			"0000000000000000000000000000000000000000000000000000000000000000" +
+			"0000000000000000000000000000000000000000000000000000000000000000" +
+			"0000000000000000000000000000000000000000000000000000000000000000" +
+			"0000000000000000000000000000000000000000000000000000000000000000" +
+			"0000000000000000000000000000000000000000000000000000000000000000" +
+			"0000000000000000000000000000000000000000000000000000000000000000" +
+			"000000",
+	}, {
+		"complete HCLenTree, complete HLitTree, degenerate HDistTree, use valid HLit and HDist symbols",
+		"0cc2010d00000082b0ac4aff0eb07d27060000ffff",
+		"616263616263",
+	}, {
+		"fixed block, use reserved symbol 287",
+		"33180700",
+		"fail",
+	}, {
+		"raw block",
+		"010100feff11",
+		"11",
+	}, {
+		"issue 10426 - over-subscribed HCLenTree causes a hang",
+		"344c4a4e494d4b070000ff2e2eff2e2e2e2e2eff",
+		"fail",
+	}, {
+		"issue 11030 - empty HDistTree unexpectedly leads to error",
+		"05c0070600000080400fff37a0ca",
+		"",
+	}, {
+		"issue 11033 - empty HDistTree unexpectedly leads to error",
+		"050fb109c020cca5d017dcbca044881ee1034ec149c8980bbc413c2ab35be9dc" +
+			"b1473449922449922411202306ee97b0383a521b4ffdcf3217f9f7d3adb701",
+		"3130303634342068652e706870005d05355f7ed957ff084a90925d19e3ebc6d0" +
+			"c6d7",
+	}}
+
+	for i, tc := range testCases {
+		data, err := hex.DecodeString(tc.stream)
+		if err != nil {
+			t.Fatal(err)
+		}
+		data, err = io.ReadAll(NewReader(bytes.NewReader(data)))
+		if tc.want == "fail" {
+			if err == nil {
+				t.Errorf("#%d (%s): got nil error, want non-nil", i, tc.desc)
+			}
+		} else {
+			if err != nil {
+				t.Errorf("#%d (%s): %v", i, tc.desc, err)
+				continue
+			}
+			if got := hex.EncodeToString(data); got != tc.want {
+				t.Errorf("#%d (%s):\ngot  %q\nwant %q", i, tc.desc, got, tc.want)
+			}
+
+		}
+	}
+}
+
+func TestTruncatedStreams(t *testing.T) {
+	const data = "\x00\f\x00\xf3\xffhello, world\x01\x00\x00\xff\xff"
+
+	for i := 0; i < len(data)-1; i++ {
+		r := NewReader(strings.NewReader(data[:i]))
+		_, err := io.Copy(io.Discard, r)
+		if err != io.ErrUnexpectedEOF {
+			t.Errorf("io.Copy(%d) on truncated stream: got %v, want %v", i, err, io.ErrUnexpectedEOF)
+		}
+	}
+}
+
+// Verify that flate.Reader.Read returns (n, io.EOF) instead
+// of (n, nil) + (0, io.EOF) when possible.
+//
+// This helps net/http.Transport reuse HTTP/1 connections more
+// aggressively.
+//
+// See https://github.com/google/go-github/pull/317 for background.
+func TestReaderEarlyEOF(t *testing.T) {
+	t.Parallel()
+	testSizes := []int{
+		1, 2, 3, 4, 5, 6, 7, 8,
+		100, 1000, 10000, 100000,
+		128, 1024, 16384, 131072,
+
+		// Testing multiples of windowSize triggers the case
+		// where Read will fail to return an early io.EOF.
+		windowSize * 1, windowSize * 2, windowSize * 3,
+	}
+
+	var maxSize int
+	for _, n := range testSizes {
+		if maxSize < n {
+			maxSize = n
+		}
+	}
+
+	readBuf := make([]byte, 40)
+	data := make([]byte, maxSize)
+	for i := range data {
+		data[i] = byte(i)
+	}
+
+	for _, sz := range testSizes {
+		if testing.Short() && sz > windowSize {
+			continue
+		}
+		for _, flush := range []bool{true, false} {
+			earlyEOF := true // Do we expect early io.EOF?
+
+			var buf bytes.Buffer
+			w, _ := NewWriter(&buf, 5)
+			w.Write(data[:sz])
+			if flush {
+				// If a Flush occurs after all the actual data, the flushing
+				// semantics dictate that we will observe a (0, io.EOF) since
+				// Read must return data before it knows that the stream ended.
+				w.Flush()
+				earlyEOF = false
+			}
+			w.Close()
+
+			r := NewReader(&buf)
+			for {
+				n, err := r.Read(readBuf)
+				if err == io.EOF {
+					// If the availWrite == windowSize, then that means that the
+					// previous Read returned because the write buffer was full
+					// and it just so happened that the stream had no more data.
+					// This situation is rare, but unavoidable.
+					if r.(*decompressor).dict.availWrite() == windowSize {
+						earlyEOF = false
+					}
+
+					if n == 0 && earlyEOF {
+						t.Errorf("On size:%d flush:%v, Read() = (0, io.EOF), want (n, io.EOF)", sz, flush)
+					}
+					if n != 0 && !earlyEOF {
+						t.Errorf("On size:%d flush:%v, Read() = (%d, io.EOF), want (0, io.EOF)", sz, flush, n)
+					}
+					break
+				}
+				if err != nil {
+					t.Fatal(err)
+				}
+			}
+		}
+	}
+}
diff --git a/src/compress/flate/huffman_bit_writer.go b/src/compress/flate/huffman_bit_writer.go
new file mode 100644
index 0000000..b3ae76d
--- /dev/null
+++ b/src/compress/flate/huffman_bit_writer.go
@@ -0,0 +1,704 @@
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package flate
+
+import (
+	"io"
+)
+
+const (
+	// The largest offset code.
+	offsetCodeCount = 30
+
+	// The special code used to mark the end of a block.
+	endBlockMarker = 256
+
+	// The first length code.
+	lengthCodesStart = 257
+
+	// The number of codegen codes.
+	codegenCodeCount = 19
+	badCode          = 255
+
+	// bufferFlushSize indicates the buffer size
+	// after which bytes are flushed to the writer.
+	// Should preferably be a multiple of 6, since
+	// we accumulate 6 bytes between writes to the buffer.
+	bufferFlushSize = 240
+
+	// bufferSize is the actual output byte buffer size.
+	// It must have additional headroom for a flush
+	// which can contain up to 8 bytes.
+	bufferSize = bufferFlushSize + 8
+)
+
+// The number of extra bits needed by length code X - LENGTH_CODES_START.
+var lengthExtraBits = []int8{
+	/* 257 */ 0, 0, 0,
+	/* 260 */ 0, 0, 0, 0, 0, 1, 1, 1, 1, 2,
+	/* 270 */ 2, 2, 2, 3, 3, 3, 3, 4, 4, 4,
+	/* 280 */ 4, 5, 5, 5, 5, 0,
+}
+
+// The length indicated by length code X - LENGTH_CODES_START.
+var lengthBase = []uint32{
+	0, 1, 2, 3, 4, 5, 6, 7, 8, 10,
+	12, 14, 16, 20, 24, 28, 32, 40, 48, 56,
+	64, 80, 96, 112, 128, 160, 192, 224, 255,
+}
+
+// offset code word extra bits.
+var offsetExtraBits = []int8{
+	0, 0, 0, 0, 1, 1, 2, 2, 3, 3,
+	4, 4, 5, 5, 6, 6, 7, 7, 8, 8,
+	9, 9, 10, 10, 11, 11, 12, 12, 13, 13,
+}
+
+var offsetBase = []uint32{
+	0x000000, 0x000001, 0x000002, 0x000003, 0x000004,
+	0x000006, 0x000008, 0x00000c, 0x000010, 0x000018,
+	0x000020, 0x000030, 0x000040, 0x000060, 0x000080,
+	0x0000c0, 0x000100, 0x000180, 0x000200, 0x000300,
+	0x000400, 0x000600, 0x000800, 0x000c00, 0x001000,
+	0x001800, 0x002000, 0x003000, 0x004000, 0x006000,
+}
+
+// The odd order in which the codegen code sizes are written.
+var codegenOrder = []uint32{16, 17, 18, 0, 8, 7, 9, 6, 10, 5, 11, 4, 12, 3, 13, 2, 14, 1, 15}
+
+type huffmanBitWriter struct {
+	// writer is the underlying writer.
+	// Do not use it directly; use the write method, which ensures
+	// that Write errors are sticky.
+	writer io.Writer
+
+	// Data waiting to be written is bytes[0:nbytes]
+	// and then the low nbits of bits.  Data is always written
+	// sequentially into the bytes array.
+	bits            uint64
+	nbits           uint
+	bytes           [bufferSize]byte
+	codegenFreq     [codegenCodeCount]int32
+	nbytes          int
+	literalFreq     []int32
+	offsetFreq      []int32
+	codegen         []uint8
+	literalEncoding *huffmanEncoder
+	offsetEncoding  *huffmanEncoder
+	codegenEncoding *huffmanEncoder
+	err             error
+}
+
+func newHuffmanBitWriter(w io.Writer) *huffmanBitWriter {
+	return &huffmanBitWriter{
+		writer:          w,
+		literalFreq:     make([]int32, maxNumLit),
+		offsetFreq:      make([]int32, offsetCodeCount),
+		codegen:         make([]uint8, maxNumLit+offsetCodeCount+1),
+		literalEncoding: newHuffmanEncoder(maxNumLit),
+		codegenEncoding: newHuffmanEncoder(codegenCodeCount),
+		offsetEncoding:  newHuffmanEncoder(offsetCodeCount),
+	}
+}
+
+func (w *huffmanBitWriter) reset(writer io.Writer) {
+	w.writer = writer
+	w.bits, w.nbits, w.nbytes, w.err = 0, 0, 0, nil
+}
+
+func (w *huffmanBitWriter) flush() {
+	if w.err != nil {
+		w.nbits = 0
+		return
+	}
+	n := w.nbytes
+	for w.nbits != 0 {
+		w.bytes[n] = byte(w.bits)
+		w.bits >>= 8
+		if w.nbits > 8 { // Avoid underflow
+			w.nbits -= 8
+		} else {
+			w.nbits = 0
+		}
+		n++
+	}
+	w.bits = 0
+	w.write(w.bytes[:n])
+	w.nbytes = 0
+}
+
+func (w *huffmanBitWriter) write(b []byte) {
+	if w.err != nil {
+		return
+	}
+	_, w.err = w.writer.Write(b)
+}
+
+func (w *huffmanBitWriter) writeBits(b int32, nb uint) {
+	if w.err != nil {
+		return
+	}
+	w.bits |= uint64(b) << w.nbits
+	w.nbits += nb
+	if w.nbits >= 48 {
+		bits := w.bits
+		w.bits >>= 48
+		w.nbits -= 48
+		n := w.nbytes
+		bytes := w.bytes[n : n+6]
+		bytes[0] = byte(bits)
+		bytes[1] = byte(bits >> 8)
+		bytes[2] = byte(bits >> 16)
+		bytes[3] = byte(bits >> 24)
+		bytes[4] = byte(bits >> 32)
+		bytes[5] = byte(bits >> 40)
+		n += 6
+		if n >= bufferFlushSize {
+			w.write(w.bytes[:n])
+			n = 0
+		}
+		w.nbytes = n
+	}
+}
+
+func (w *huffmanBitWriter) writeBytes(bytes []byte) {
+	if w.err != nil {
+		return
+	}
+	n := w.nbytes
+	if w.nbits&7 != 0 {
+		w.err = InternalError("writeBytes with unfinished bits")
+		return
+	}
+	for w.nbits != 0 {
+		w.bytes[n] = byte(w.bits)
+		w.bits >>= 8
+		w.nbits -= 8
+		n++
+	}
+	if n != 0 {
+		w.write(w.bytes[:n])
+	}
+	w.nbytes = 0
+	w.write(bytes)
+}
+
+// RFC 1951 3.2.7 specifies a special run-length encoding for specifying
+// the literal and offset lengths arrays (which are concatenated into a single
+// array).  This method generates that run-length encoding.
+//
+// The result is written into the codegen array, and the frequencies
+// of each code is written into the codegenFreq array.
+// Codes 0-15 are single byte codes. Codes 16-18 are followed by additional
+// information. Code badCode is an end marker
+//
+//  numLiterals      The number of literals in literalEncoding
+//  numOffsets       The number of offsets in offsetEncoding
+//  litenc, offenc   The literal and offset encoder to use
+func (w *huffmanBitWriter) generateCodegen(numLiterals int, numOffsets int, litEnc, offEnc *huffmanEncoder) {
+	for i := range w.codegenFreq {
+		w.codegenFreq[i] = 0
+	}
+	// Note that we are using codegen both as a temporary variable for holding
+	// a copy of the frequencies, and as the place where we put the result.
+	// This is fine because the output is always shorter than the input used
+	// so far.
+	codegen := w.codegen // cache
+	// Copy the concatenated code sizes to codegen. Put a marker at the end.
+	cgnl := codegen[:numLiterals]
+	for i := range cgnl {
+		cgnl[i] = uint8(litEnc.codes[i].len)
+	}
+
+	cgnl = codegen[numLiterals : numLiterals+numOffsets]
+	for i := range cgnl {
+		cgnl[i] = uint8(offEnc.codes[i].len)
+	}
+	codegen[numLiterals+numOffsets] = badCode
+
+	size := codegen[0]
+	count := 1
+	outIndex := 0
+	for inIndex := 1; size != badCode; inIndex++ {
+		// INVARIANT: We have seen "count" copies of size that have not yet
+		// had output generated for them.
+		nextSize := codegen[inIndex]
+		if nextSize == size {
+			count++
+			continue
+		}
+		// We need to generate codegen indicating "count" of size.
+		if size != 0 {
+			codegen[outIndex] = size
+			outIndex++
+			w.codegenFreq[size]++
+			count--
+			for count >= 3 {
+				n := 6
+				if n > count {
+					n = count
+				}
+				codegen[outIndex] = 16
+				outIndex++
+				codegen[outIndex] = uint8(n - 3)
+				outIndex++
+				w.codegenFreq[16]++
+				count -= n
+			}
+		} else {
+			for count >= 11 {
+				n := 138
+				if n > count {
+					n = count
+				}
+				codegen[outIndex] = 18
+				outIndex++
+				codegen[outIndex] = uint8(n - 11)
+				outIndex++
+				w.codegenFreq[18]++
+				count -= n
+			}
+			if count >= 3 {
+				// count >= 3 && count <= 10
+				codegen[outIndex] = 17
+				outIndex++
+				codegen[outIndex] = uint8(count - 3)
+				outIndex++
+				w.codegenFreq[17]++
+				count = 0
+			}
+		}
+		count--
+		for ; count >= 0; count-- {
+			codegen[outIndex] = size
+			outIndex++
+			w.codegenFreq[size]++
+		}
+		// Set up invariant for next time through the loop.
+		size = nextSize
+		count = 1
+	}
+	// Marker indicating the end of the codegen.
+	codegen[outIndex] = badCode
+}
+
+// dynamicSize returns the size of dynamically encoded data in bits.
+func (w *huffmanBitWriter) dynamicSize(litEnc, offEnc *huffmanEncoder, extraBits int) (size, numCodegens int) {
+	numCodegens = len(w.codegenFreq)
+	for numCodegens > 4 && w.codegenFreq[codegenOrder[numCodegens-1]] == 0 {
+		numCodegens--
+	}
+	header := 3 + 5 + 5 + 4 + (3 * numCodegens) +
+		w.codegenEncoding.bitLength(w.codegenFreq[:]) +
+		int(w.codegenFreq[16])*2 +
+		int(w.codegenFreq[17])*3 +
+		int(w.codegenFreq[18])*7
+	size = header +
+		litEnc.bitLength(w.literalFreq) +
+		offEnc.bitLength(w.offsetFreq) +
+		extraBits
+
+	return size, numCodegens
+}
+
+// fixedSize returns the size of dynamically encoded data in bits.
+func (w *huffmanBitWriter) fixedSize(extraBits int) int {
+	return 3 +
+		fixedLiteralEncoding.bitLength(w.literalFreq) +
+		fixedOffsetEncoding.bitLength(w.offsetFreq) +
+		extraBits
+}
+
+// storedSize calculates the stored size, including header.
+// The function returns the size in bits and whether the block
+// fits inside a single block.
+func (w *huffmanBitWriter) storedSize(in []byte) (int, bool) {
+	if in == nil {
+		return 0, false
+	}
+	if len(in) <= maxStoreBlockSize {
+		return (len(in) + 5) * 8, true
+	}
+	return 0, false
+}
+
+func (w *huffmanBitWriter) writeCode(c hcode) {
+	if w.err != nil {
+		return
+	}
+	w.bits |= uint64(c.code) << w.nbits
+	w.nbits += uint(c.len)
+	if w.nbits >= 48 {
+		bits := w.bits
+		w.bits >>= 48
+		w.nbits -= 48
+		n := w.nbytes
+		bytes := w.bytes[n : n+6]
+		bytes[0] = byte(bits)
+		bytes[1] = byte(bits >> 8)
+		bytes[2] = byte(bits >> 16)
+		bytes[3] = byte(bits >> 24)
+		bytes[4] = byte(bits >> 32)
+		bytes[5] = byte(bits >> 40)
+		n += 6
+		if n >= bufferFlushSize {
+			w.write(w.bytes[:n])
+			n = 0
+		}
+		w.nbytes = n
+	}
+}
+
+// Write the header of a dynamic Huffman block to the output stream.
+//
+//  numLiterals  The number of literals specified in codegen
+//  numOffsets   The number of offsets specified in codegen
+//  numCodegens  The number of codegens used in codegen
+func (w *huffmanBitWriter) writeDynamicHeader(numLiterals int, numOffsets int, numCodegens int, isEof bool) {
+	if w.err != nil {
+		return
+	}
+	var firstBits int32 = 4
+	if isEof {
+		firstBits = 5
+	}
+	w.writeBits(firstBits, 3)
+	w.writeBits(int32(numLiterals-257), 5)
+	w.writeBits(int32(numOffsets-1), 5)
+	w.writeBits(int32(numCodegens-4), 4)
+
+	for i := 0; i < numCodegens; i++ {
+		value := uint(w.codegenEncoding.codes[codegenOrder[i]].len)
+		w.writeBits(int32(value), 3)
+	}
+
+	i := 0
+	for {
+		var codeWord int = int(w.codegen[i])
+		i++
+		if codeWord == badCode {
+			break
+		}
+		w.writeCode(w.codegenEncoding.codes[uint32(codeWord)])
+
+		switch codeWord {
+		case 16:
+			w.writeBits(int32(w.codegen[i]), 2)
+			i++
+			break
+		case 17:
+			w.writeBits(int32(w.codegen[i]), 3)
+			i++
+			break
+		case 18:
+			w.writeBits(int32(w.codegen[i]), 7)
+			i++
+			break
+		}
+	}
+}
+
+func (w *huffmanBitWriter) writeStoredHeader(length int, isEof bool) {
+	if w.err != nil {
+		return
+	}
+	var flag int32
+	if isEof {
+		flag = 1
+	}
+	w.writeBits(flag, 3)
+	w.flush()
+	w.writeBits(int32(length), 16)
+	w.writeBits(int32(^uint16(length)), 16)
+}
+
+func (w *huffmanBitWriter) writeFixedHeader(isEof bool) {
+	if w.err != nil {
+		return
+	}
+	// Indicate that we are a fixed Huffman block
+	var value int32 = 2
+	if isEof {
+		value = 3
+	}
+	w.writeBits(value, 3)
+}
+
+// writeBlock will write a block of tokens with the smallest encoding.
+// The original input can be supplied, and if the huffman encoded data
+// is larger than the original bytes, the data will be written as a
+// stored block.
+// If the input is nil, the tokens will always be Huffman encoded.
+func (w *huffmanBitWriter) writeBlock(tokens []token, eof bool, input []byte) {
+	if w.err != nil {
+		return
+	}
+
+	tokens = append(tokens, endBlockMarker)
+	numLiterals, numOffsets := w.indexTokens(tokens)
+
+	var extraBits int
+	storedSize, storable := w.storedSize(input)
+	if storable {
+		// We only bother calculating the costs of the extra bits required by
+		// the length of offset fields (which will be the same for both fixed
+		// and dynamic encoding), if we need to compare those two encodings
+		// against stored encoding.
+		for lengthCode := lengthCodesStart + 8; lengthCode < numLiterals; lengthCode++ {
+			// First eight length codes have extra size = 0.
+			extraBits += int(w.literalFreq[lengthCode]) * int(lengthExtraBits[lengthCode-lengthCodesStart])
+		}
+		for offsetCode := 4; offsetCode < numOffsets; offsetCode++ {
+			// First four offset codes have extra size = 0.
+			extraBits += int(w.offsetFreq[offsetCode]) * int(offsetExtraBits[offsetCode])
+		}
+	}
+
+	// Figure out smallest code.
+	// Fixed Huffman baseline.
+	var literalEncoding = fixedLiteralEncoding
+	var offsetEncoding = fixedOffsetEncoding
+	var size = w.fixedSize(extraBits)
+
+	// Dynamic Huffman?
+	var numCodegens int
+
+	// Generate codegen and codegenFrequencies, which indicates how to encode
+	// the literalEncoding and the offsetEncoding.
+	w.generateCodegen(numLiterals, numOffsets, w.literalEncoding, w.offsetEncoding)
+	w.codegenEncoding.generate(w.codegenFreq[:], 7)
+	dynamicSize, numCodegens := w.dynamicSize(w.literalEncoding, w.offsetEncoding, extraBits)
+
+	if dynamicSize < size {
+		size = dynamicSize
+		literalEncoding = w.literalEncoding
+		offsetEncoding = w.offsetEncoding
+	}
+
+	// Stored bytes?
+	if storable && storedSize < size {
+		w.writeStoredHeader(len(input), eof)
+		w.writeBytes(input)
+		return
+	}
+
+	// Huffman.
+	if literalEncoding == fixedLiteralEncoding {
+		w.writeFixedHeader(eof)
+	} else {
+		w.writeDynamicHeader(numLiterals, numOffsets, numCodegens, eof)
+	}
+
+	// Write the tokens.
+	w.writeTokens(tokens, literalEncoding.codes, offsetEncoding.codes)
+}
+
+// writeBlockDynamic encodes a block using a dynamic Huffman table.
+// This should be used if the symbols used have a disproportionate
+// histogram distribution.
+// If input is supplied and the compression savings are below 1/16th of the
+// input size the block is stored.
+func (w *huffmanBitWriter) writeBlockDynamic(tokens []token, eof bool, input []byte) {
+	if w.err != nil {
+		return
+	}
+
+	tokens = append(tokens, endBlockMarker)
+	numLiterals, numOffsets := w.indexTokens(tokens)
+
+	// Generate codegen and codegenFrequencies, which indicates how to encode
+	// the literalEncoding and the offsetEncoding.
+	w.generateCodegen(numLiterals, numOffsets, w.literalEncoding, w.offsetEncoding)
+	w.codegenEncoding.generate(w.codegenFreq[:], 7)
+	size, numCodegens := w.dynamicSize(w.literalEncoding, w.offsetEncoding, 0)
+
+	// Store bytes, if we don't get a reasonable improvement.
+	if ssize, storable := w.storedSize(input); storable && ssize < (size+size>>4) {
+		w.writeStoredHeader(len(input), eof)
+		w.writeBytes(input)
+		return
+	}
+
+	// Write Huffman table.
+	w.writeDynamicHeader(numLiterals, numOffsets, numCodegens, eof)
+
+	// Write the tokens.
+	w.writeTokens(tokens, w.literalEncoding.codes, w.offsetEncoding.codes)
+}
+
+// indexTokens indexes a slice of tokens, and updates
+// literalFreq and offsetFreq, and generates literalEncoding
+// and offsetEncoding.
+// The number of literal and offset tokens is returned.
+func (w *huffmanBitWriter) indexTokens(tokens []token) (numLiterals, numOffsets int) {
+	for i := range w.literalFreq {
+		w.literalFreq[i] = 0
+	}
+	for i := range w.offsetFreq {
+		w.offsetFreq[i] = 0
+	}
+
+	for _, t := range tokens {
+		if t < matchType {
+			w.literalFreq[t.literal()]++
+			continue
+		}
+		length := t.length()
+		offset := t.offset()
+		w.literalFreq[lengthCodesStart+lengthCode(length)]++
+		w.offsetFreq[offsetCode(offset)]++
+	}
+
+	// get the number of literals
+	numLiterals = len(w.literalFreq)
+	for w.literalFreq[numLiterals-1] == 0 {
+		numLiterals--
+	}
+	// get the number of offsets
+	numOffsets = len(w.offsetFreq)
+	for numOffsets > 0 && w.offsetFreq[numOffsets-1] == 0 {
+		numOffsets--
+	}
+	if numOffsets == 0 {
+		// We haven't found a single match. If we want to go with the dynamic encoding,
+		// we should count at least one offset to be sure that the offset huffman tree could be encoded.
+		w.offsetFreq[0] = 1
+		numOffsets = 1
+	}
+	w.literalEncoding.generate(w.literalFreq, 15)
+	w.offsetEncoding.generate(w.offsetFreq, 15)
+	return
+}
+
+// writeTokens writes a slice of tokens to the output.
+// codes for literal and offset encoding must be supplied.
+func (w *huffmanBitWriter) writeTokens(tokens []token, leCodes, oeCodes []hcode) {
+	if w.err != nil {
+		return
+	}
+	for _, t := range tokens {
+		if t < matchType {
+			w.writeCode(leCodes[t.literal()])
+			continue
+		}
+		// Write the length
+		length := t.length()
+		lengthCode := lengthCode(length)
+		w.writeCode(leCodes[lengthCode+lengthCodesStart])
+		extraLengthBits := uint(lengthExtraBits[lengthCode])
+		if extraLengthBits > 0 {
+			extraLength := int32(length - lengthBase[lengthCode])
+			w.writeBits(extraLength, extraLengthBits)
+		}
+		// Write the offset
+		offset := t.offset()
+		offsetCode := offsetCode(offset)
+		w.writeCode(oeCodes[offsetCode])
+		extraOffsetBits := uint(offsetExtraBits[offsetCode])
+		if extraOffsetBits > 0 {
+			extraOffset := int32(offset - offsetBase[offsetCode])
+			w.writeBits(extraOffset, extraOffsetBits)
+		}
+	}
+}
+
+// huffOffset is a static offset encoder used for huffman only encoding.
+// It can be reused since we will not be encoding offset values.
+var huffOffset *huffmanEncoder
+
+func init() {
+	offsetFreq := make([]int32, offsetCodeCount)
+	offsetFreq[0] = 1
+	huffOffset = newHuffmanEncoder(offsetCodeCount)
+	huffOffset.generate(offsetFreq, 15)
+}
+
+// writeBlockHuff encodes a block of bytes as either
+// Huffman encoded literals or uncompressed bytes if the
+// results only gains very little from compression.
+func (w *huffmanBitWriter) writeBlockHuff(eof bool, input []byte) {
+	if w.err != nil {
+		return
+	}
+
+	// Clear histogram
+	for i := range w.literalFreq {
+		w.literalFreq[i] = 0
+	}
+
+	// Add everything as literals
+	histogram(input, w.literalFreq)
+
+	w.literalFreq[endBlockMarker] = 1
+
+	const numLiterals = endBlockMarker + 1
+	w.offsetFreq[0] = 1
+	const numOffsets = 1
+
+	w.literalEncoding.generate(w.literalFreq, 15)
+
+	// Figure out smallest code.
+	// Always use dynamic Huffman or Store
+	var numCodegens int
+
+	// Generate codegen and codegenFrequencies, which indicates how to encode
+	// the literalEncoding and the offsetEncoding.
+	w.generateCodegen(numLiterals, numOffsets, w.literalEncoding, huffOffset)
+	w.codegenEncoding.generate(w.codegenFreq[:], 7)
+	size, numCodegens := w.dynamicSize(w.literalEncoding, huffOffset, 0)
+
+	// Store bytes, if we don't get a reasonable improvement.
+	if ssize, storable := w.storedSize(input); storable && ssize < (size+size>>4) {
+		w.writeStoredHeader(len(input), eof)
+		w.writeBytes(input)
+		return
+	}
+
+	// Huffman.
+	w.writeDynamicHeader(numLiterals, numOffsets, numCodegens, eof)
+	encoding := w.literalEncoding.codes[:257]
+	n := w.nbytes
+	for _, t := range input {
+		// Bitwriting inlined, ~30% speedup
+		c := encoding[t]
+		w.bits |= uint64(c.code) << w.nbits
+		w.nbits += uint(c.len)
+		if w.nbits < 48 {
+			continue
+		}
+		// Store 6 bytes
+		bits := w.bits
+		w.bits >>= 48
+		w.nbits -= 48
+		bytes := w.bytes[n : n+6]
+		bytes[0] = byte(bits)
+		bytes[1] = byte(bits >> 8)
+		bytes[2] = byte(bits >> 16)
+		bytes[3] = byte(bits >> 24)
+		bytes[4] = byte(bits >> 32)
+		bytes[5] = byte(bits >> 40)
+		n += 6
+		if n < bufferFlushSize {
+			continue
+		}
+		w.write(w.bytes[:n])
+		if w.err != nil {
+			return // Return early in the event of write failures
+		}
+		n = 0
+	}
+	w.nbytes = n
+	w.writeCode(encoding[endBlockMarker])
+}
+
+// histogram accumulates a histogram of b in h.
+//
+// len(h) must be >= 256, and h's elements must be all zeroes.
+func histogram(b []byte, h []int32) {
+	h = h[:256]
+	for _, t := range b {
+		h[t]++
+	}
+}
diff --git a/src/compress/flate/huffman_bit_writer_test.go b/src/compress/flate/huffman_bit_writer_test.go
new file mode 100644
index 0000000..a57799c
--- /dev/null
+++ b/src/compress/flate/huffman_bit_writer_test.go
@@ -0,0 +1,365 @@
+// Copyright 2016 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package flate
+
+import (
+	"bytes"
+	"flag"
+	"fmt"
+	"os"
+	"path/filepath"
+	"strings"
+	"testing"
+)
+
+var update = flag.Bool("update", false, "update reference files")
+
+// TestBlockHuff tests huffman encoding against reference files
+// to detect possible regressions.
+// If encoding/bit allocation changes you can regenerate these files
+// by using the -update flag.
+func TestBlockHuff(t *testing.T) {
+	// determine input files
+	match, err := filepath.Glob("testdata/huffman-*.in")
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	for _, in := range match {
+		out := in // for files where input and output are identical
+		if strings.HasSuffix(in, ".in") {
+			out = in[:len(in)-len(".in")] + ".golden"
+		}
+		testBlockHuff(t, in, out)
+	}
+}
+
+func testBlockHuff(t *testing.T, in, out string) {
+	all, err := os.ReadFile(in)
+	if err != nil {
+		t.Error(err)
+		return
+	}
+	var buf bytes.Buffer
+	bw := newHuffmanBitWriter(&buf)
+	bw.writeBlockHuff(false, all)
+	bw.flush()
+	got := buf.Bytes()
+
+	want, err := os.ReadFile(out)
+	if err != nil && !*update {
+		t.Error(err)
+		return
+	}
+
+	t.Logf("Testing %q", in)
+	if !bytes.Equal(got, want) {
+		if *update {
+			if in != out {
+				t.Logf("Updating %q", out)
+				if err := os.WriteFile(out, got, 0666); err != nil {
+					t.Error(err)
+				}
+				return
+			}
+			// in == out: don't accidentally destroy input
+			t.Errorf("WARNING: -update did not rewrite input file %s", in)
+		}
+
+		t.Errorf("%q != %q (see %q)", in, out, in+".got")
+		if err := os.WriteFile(in+".got", got, 0666); err != nil {
+			t.Error(err)
+		}
+		return
+	}
+	t.Log("Output ok")
+
+	// Test if the writer produces the same output after reset.
+	buf.Reset()
+	bw.reset(&buf)
+	bw.writeBlockHuff(false, all)
+	bw.flush()
+	got = buf.Bytes()
+	if !bytes.Equal(got, want) {
+		t.Errorf("after reset %q != %q (see %q)", in, out, in+".reset.got")
+		if err := os.WriteFile(in+".reset.got", got, 0666); err != nil {
+			t.Error(err)
+		}
+		return
+	}
+	t.Log("Reset ok")
+	testWriterEOF(t, "huff", huffTest{input: in}, true)
+}
+
+type huffTest struct {
+	tokens      []token
+	input       string // File name of input data matching the tokens.
+	want        string // File name of data with the expected output with input available.
+	wantNoInput string // File name of the expected output when no input is available.
+}
+
+const ml = 0x7fc00000 // Maximum length token. Used to reduce the size of writeBlockTests
+
+var writeBlockTests = []huffTest{
+	{
+		input:       "testdata/huffman-null-max.in",
+		want:        "testdata/huffman-null-max.%s.expect",
+		wantNoInput: "testdata/huffman-null-max.%s.expect-noinput",
+		tokens:      []token{0x0, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, 0x0, 0x0},
+	},
+	{
+		input:       "testdata/huffman-pi.in",
+		want:        "testdata/huffman-pi.%s.expect",
+		wantNoInput: "testdata/huffman-pi.%s.expect-noinput",
+		tokens:      []token{0x33, 0x2e, 0x31, 0x34, 0x31, 0x35, 0x39, 0x32, 0x36, 0x35, 0x33, 0x35, 0x38, 0x39, 0x37, 0x39, 0x33, 0x32, 0x33, 0x38, 0x34, 0x36, 0x32, 0x36, 0x34, 0x33, 0x33, 0x38, 0x33, 0x32, 0x37, 0x39, 0x35, 0x30, 0x32, 0x38, 0x38, 0x34, 0x31, 0x39, 0x37, 0x31, 0x36, 0x39, 0x33, 0x39, 0x39, 0x33, 0x37, 0x35, 0x31, 0x30, 0x35, 0x38, 0x32, 0x30, 0x39, 0x37, 0x34, 0x39, 0x34, 0x34, 0x35, 0x39, 0x32, 0x33, 0x30, 0x37, 0x38, 0x31, 0x36, 0x34, 0x30, 0x36, 0x32, 0x38, 0x36, 0x32, 0x30, 0x38, 0x39, 0x39, 0x38, 0x36, 0x32, 0x38, 0x30, 0x33, 0x34, 0x38, 0x32, 0x35, 0x33, 0x34, 0x32, 0x31, 0x31, 0x37, 0x30, 0x36, 0x37, 0x39, 0x38, 0x32, 0x31, 0x34, 0x38, 0x30, 0x38, 0x36, 0x35, 0x31, 0x33, 0x32, 0x38, 0x32, 0x33, 0x30, 0x36, 0x36, 0x34, 0x37, 0x30, 0x39, 0x33, 0x38, 0x34, 0x34, 0x36, 0x30, 0x39, 0x35, 0x35, 0x30, 0x35, 0x38, 0x32, 0x32, 0x33, 0x31, 0x37, 0x32, 0x35, 0x33, 0x35, 0x39, 0x34, 0x30, 0x38, 0x31, 0x32, 0x38, 0x34, 0x38, 0x31, 0x31, 0x31, 0x37, 0x34, 0x4040007e, 0x34, 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+	},
+	{
+		input:       "testdata/huffman-rand-1k.in",
+		want:        "testdata/huffman-rand-1k.%s.expect",
+		wantNoInput: "testdata/huffman-rand-1k.%s.expect-noinput",
+		tokens:      []token{0xf8, 0x8b, 0x96, 0x76, 0x48, 0xd, 0x85, 0x94, 0x25, 0x80, 0xaf, 0xc2, 0xfe, 0x8d, 0xe8, 0x20, 0xeb, 0x17, 0x86, 0xc9, 0xb7, 0xc5, 0xde, 0x6, 0xea, 0x7d, 0x18, 0x8b, 0xe7, 0x3e, 0x7, 0xda, 0xdf, 0xff, 0x6c, 0x73, 0xde, 0xcc, 0xe7, 0x6d, 0x8d, 0x4, 0x19, 0x49, 0x7f, 0x47, 0x1f, 0x48, 0x15, 0xb0, 0xe8, 0x9e, 0xf2, 0x31, 0x59, 0xde, 0x34, 0xb4, 0x5b, 0xe5, 0xe0, 0x9, 0x11, 0x30, 0xc2, 0x88, 0x5b, 0x7c, 0x5d, 0x14, 0x13, 0x6f, 0x23, 0xa9, 0xd, 0xbc, 0x2d, 0x23, 0xbe, 0xd9, 0xed, 0x75, 0x4, 0x6c, 0x99, 0xdf, 0xfd, 0x70, 0x66, 0xe6, 0xee, 0xd9, 0xb1, 0x9e, 0x6e, 0x83, 0x59, 0xd5, 0xd4, 0x80, 0x59, 0x98, 0x77, 0x89, 0x43, 0x38, 0xc9, 0xaf, 0x30, 0x32, 0x9a, 0x20, 0x1b, 0x46, 0x3d, 0x67, 0x6e, 0xd7, 0x72, 0x9e, 0x4e, 0x21, 0x4f, 0xc6, 0xe0, 0xd4, 0x7b, 0x4, 0x8d, 0xa5, 0x3, 0xf6, 0x5, 0x9b, 0x6b, 0xdc, 0x2a, 0x93, 0x77, 0x28, 0xfd, 0xb4, 0x62, 0xda, 0x20, 0xe7, 0x1f, 0xab, 0x6b, 0x51, 0x43, 0x39, 0x2f, 0xa0, 0x92, 0x1, 0x6c, 0x75, 0x3e, 0xf4, 0x35, 0xfd, 0x43, 0x2e, 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+	},
+	{
+		input:       "testdata/huffman-rand-limit.in",
+		want:        "testdata/huffman-rand-limit.%s.expect",
+		wantNoInput: "testdata/huffman-rand-limit.%s.expect-noinput",
+		tokens:      []token{0x61, 0x51c00000, 0xa, 0xf8, 0x8b, 0x96, 0x76, 0x48, 0xa, 0x85, 0x94, 0x25, 0x80, 0xaf, 0xc2, 0xfe, 0x8d, 0xe8, 0x20, 0xeb, 0x17, 0x86, 0xc9, 0xb7, 0xc5, 0xde, 0x6, 0xea, 0x7d, 0x18, 0x8b, 0xe7, 0x3e, 0x7, 0xda, 0xdf, 0xff, 0x6c, 0x73, 0xde, 0xcc, 0xe7, 0x6d, 0x8d, 0x4, 0x19, 0x49, 0x7f, 0x47, 0x1f, 0x48, 0x15, 0xb0, 0xe8, 0x9e, 0xf2, 0x31, 0x59, 0xde, 0x34, 0xb4, 0x5b, 0xe5, 0xe0, 0x9, 0x11, 0x30, 0xc2, 0x88, 0x5b, 0x7c, 0x5d, 0x14, 0x13, 0x6f, 0x23, 0xa9, 0xa, 0xbc, 0x2d, 0x23, 0xbe, 0xd9, 0xed, 0x75, 0x4, 0x6c, 0x99, 0xdf, 0xfd, 0x70, 0x66, 0xe6, 0xee, 0xd9, 0xb1, 0x9e, 0x6e, 0x83, 0x59, 0xd5, 0xd4, 0x80, 0x59, 0x98, 0x77, 0x89, 0x43, 0x38, 0xc9, 0xaf, 0x30, 0x32, 0x9a, 0x20, 0x1b, 0x46, 0x3d, 0x67, 0x6e, 0xd7, 0x72, 0x9e, 0x4e, 0x21, 0x4f, 0xc6, 0xe0, 0xd4, 0x7b, 0x4, 0x8d, 0xa5, 0x3, 0xf6, 0x5, 0x9b, 0x6b, 0xdc, 0x2a, 0x93, 0x77, 0x28, 0xfd, 0xb4, 0x62, 0xda, 0x20, 0xe7, 0x1f, 0xab, 0x6b, 0x51, 0x43, 0x39, 0x2f, 0xa0, 0x92, 0x1, 0x6c, 0x75, 0x3e, 0xf4, 0x35, 0xfd, 0x43, 0x2e, 0xf7, 0xa4, 0x75, 0xda, 0xea, 0x9b, 0xa},
+	},
+	{
+		input:       "testdata/huffman-shifts.in",
+		want:        "testdata/huffman-shifts.%s.expect",
+		wantNoInput: "testdata/huffman-shifts.%s.expect-noinput",
+		tokens:      []token{0x31, 0x30, 0x7fc00001, 0x7fc00001, 0x7fc00001, 0x7fc00001, 0x7fc00001, 0x7fc00001, 0x7fc00001, 0x7fc00001, 0x7fc00001, 0x7fc00001, 0x7fc00001, 0x7fc00001, 0x7fc00001, 0x7fc00001, 0x7fc00001, 0x52400001, 0xd, 0xa, 0x32, 0x33, 0x7fc00001, 0x7fc00001, 0x7fc00001, 0x7fc00001, 0x7fc00001, 0x7fc00001, 0x7fc00001, 0x7fc00001, 0x7fc00001, 0x7f400001},
+	},
+	{
+		input:       "testdata/huffman-text-shift.in",
+		want:        "testdata/huffman-text-shift.%s.expect",
+		wantNoInput: "testdata/huffman-text-shift.%s.expect-noinput",
+		tokens:      []token{0x2f, 0x2f, 0x43, 0x6f, 0x70, 0x79, 0x72, 0x69, 0x67, 0x68, 0x74, 0x32, 0x30, 0x30, 0x39, 0x54, 0x68, 0x47, 0x6f, 0x41, 0x75, 0x74, 0x68, 0x6f, 0x72, 0x2e, 0x41, 0x6c, 0x6c, 0x40800016, 0x72, 0x72, 0x76, 0x64, 0x2e, 0xd, 0xa, 0x2f, 0x2f, 0x55, 0x6f, 0x66, 0x74, 0x68, 0x69, 0x6f, 0x75, 0x72, 0x63, 0x63, 0x6f, 0x64, 0x69, 0x67, 0x6f, 0x76, 0x72, 0x6e, 0x64, 0x62, 0x79, 0x42, 0x53, 0x44, 0x2d, 0x74, 0x79, 0x6c, 0x40400020, 0x6c, 0x69, 0x63, 0x6e, 0x74, 0x68, 0x74, 0x63, 0x6e, 0x62, 0x66, 0x6f, 0x75, 0x6e, 0x64, 0x69, 0x6e, 0x74, 0x68, 0x4c, 0x49, 0x43, 0x45, 0x4e, 0x53, 0x45, 0x66, 0x69, 0x6c, 0x2e, 0xd, 0xa, 0xd, 0xa, 0x70, 0x63, 0x6b, 0x67, 0x6d, 0x69, 0x6e, 0x4040000a, 0x69, 0x6d, 0x70, 0x6f, 0x72, 0x74, 0x22, 0x6f, 0x22, 0x4040000c, 0x66, 0x75, 0x6e, 0x63, 0x6d, 0x69, 0x6e, 0x28, 0x29, 0x7b, 0xd, 0xa, 0x9, 0x76, 0x72, 0x62, 0x3d, 0x6d, 0x6b, 0x28, 0x5b, 0x5d, 0x62, 0x79, 0x74, 0x2c, 0x36, 0x35, 0x35, 0x33, 0x35, 0x29, 0xd, 0xa, 0x9, 0x66, 0x2c, 0x5f, 0x3a, 0x3d, 0x6f, 0x2e, 0x43, 0x72, 0x74, 0x28, 0x22, 0x68, 0x75, 0x66, 0x66, 0x6d, 0x6e, 0x2d, 0x6e, 0x75, 0x6c, 0x6c, 0x2d, 0x6d, 0x78, 0x2e, 0x69, 0x6e, 0x22, 0x40800021, 0x2e, 0x57, 0x72, 0x69, 0x74, 0x28, 0x62, 0x29, 0xd, 0xa, 0x7d, 0xd, 0xa, 0x41, 0x42, 0x43, 0x44, 0x45, 0x46, 0x47, 0x48, 0x49, 0x4a, 0x4b, 0x4c, 0x4d, 0x4e, 0x4f, 0x50, 0x51, 0x52, 0x53, 0x54, 0x55, 0x56, 0x58, 0x78, 0x79, 0x7a, 0x21, 0x22, 0x23, 0xc2, 0xa4, 0x25, 0x26, 0x2f, 0x3f, 0x22},
+	},
+	{
+		input:       "testdata/huffman-text.in",
+		want:        "testdata/huffman-text.%s.expect",
+		wantNoInput: "testdata/huffman-text.%s.expect-noinput",
+		tokens:      []token{0x2f, 0x2f, 0x20, 0x43, 0x6f, 0x70, 0x79, 0x72, 0x69, 0x67, 0x68, 0x74, 0x20, 0x32, 0x30, 0x30, 0x39, 0x20, 0x54, 0x68, 0x65, 0x20, 0x47, 0x6f, 0x20, 0x41, 0x75, 0x74, 0x68, 0x6f, 0x72, 0x73, 0x2e, 0x20, 0x41, 0x6c, 0x6c, 0x20, 0x4080001e, 0x73, 0x20, 0x72, 0x65, 0x73, 0x65, 0x72, 0x76, 0x65, 0x64, 0x2e, 0xd, 0xa, 0x2f, 0x2f, 0x20, 0x55, 0x73, 0x65, 0x20, 0x6f, 0x66, 0x20, 0x74, 0x68, 0x69, 0x73, 0x20, 0x73, 0x6f, 0x75, 0x72, 0x63, 0x65, 0x20, 0x63, 0x6f, 0x64, 0x65, 0x20, 0x69, 0x73, 0x20, 0x67, 0x6f, 0x76, 0x65, 0x72, 0x6e, 0x65, 0x64, 0x20, 0x62, 0x79, 0x20, 0x61, 0x20, 0x42, 0x53, 0x44, 0x2d, 0x73, 0x74, 0x79, 0x6c, 0x65, 0x40800036, 0x6c, 0x69, 0x63, 0x65, 0x6e, 0x73, 0x65, 0x20, 0x74, 0x68, 0x61, 0x74, 0x20, 0x63, 0x61, 0x6e, 0x20, 0x62, 0x65, 0x20, 0x66, 0x6f, 0x75, 0x6e, 0x64, 0x20, 0x69, 0x6e, 0x20, 0x74, 0x68, 0x65, 0x20, 0x4c, 0x49, 0x43, 0x45, 0x4e, 0x53, 0x45, 0x20, 0x66, 0x69, 0x6c, 0x65, 0x2e, 0xd, 0xa, 0xd, 0xa, 0x70, 0x61, 0x63, 0x6b, 0x61, 0x67, 0x65, 0x20, 0x6d, 0x61, 0x69, 0x6e, 0x4040000f, 0x69, 0x6d, 0x70, 0x6f, 0x72, 0x74, 0x20, 0x22, 0x6f, 0x73, 0x22, 0x4040000e, 0x66, 0x75, 0x6e, 0x63, 0x4080001b, 0x28, 0x29, 0x20, 0x7b, 0xd, 0xa, 0x9, 0x76, 0x61, 0x72, 0x20, 0x62, 0x20, 0x3d, 0x20, 0x6d, 0x61, 0x6b, 0x65, 0x28, 0x5b, 0x5d, 0x62, 0x79, 0x74, 0x65, 0x2c, 0x20, 0x36, 0x35, 0x35, 0x33, 0x35, 0x29, 0xd, 0xa, 0x9, 0x66, 0x2c, 0x20, 0x5f, 0x20, 0x3a, 0x3d, 0x20, 0x6f, 0x73, 0x2e, 0x43, 0x72, 0x65, 0x61, 0x74, 0x65, 0x28, 0x22, 0x68, 0x75, 0x66, 0x66, 0x6d, 0x61, 0x6e, 0x2d, 0x6e, 0x75, 0x6c, 0x6c, 0x2d, 0x6d, 0x61, 0x78, 0x2e, 0x69, 0x6e, 0x22, 0x4080002a, 0x2e, 0x57, 0x72, 0x69, 0x74, 0x65, 0x28, 0x62, 0x29, 0xd, 0xa, 0x7d, 0xd, 0xa},
+	},
+	{
+		input:       "testdata/huffman-zero.in",
+		want:        "testdata/huffman-zero.%s.expect",
+		wantNoInput: "testdata/huffman-zero.%s.expect-noinput",
+		tokens:      []token{0x30, ml, 0x4b800000},
+	},
+	{
+		input:       "",
+		want:        "",
+		wantNoInput: "testdata/null-long-match.%s.expect-noinput",
+		tokens:      []token{0x0, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, ml, 0x41400000},
+	},
+}
+
+// TestWriteBlock tests if the writeBlock encoding has changed.
+// To update the reference files use the "-update" flag on the test.
+func TestWriteBlock(t *testing.T) {
+	for _, test := range writeBlockTests {
+		testBlock(t, test, "wb")
+	}
+}
+
+// TestWriteBlockDynamic tests if the writeBlockDynamic encoding has changed.
+// To update the reference files use the "-update" flag on the test.
+func TestWriteBlockDynamic(t *testing.T) {
+	for _, test := range writeBlockTests {
+		testBlock(t, test, "dyn")
+	}
+}
+
+// testBlock tests a block against its references,
+// or regenerate the references, if "-update" flag is set.
+func testBlock(t *testing.T, test huffTest, ttype string) {
+	if test.want != "" {
+		test.want = fmt.Sprintf(test.want, ttype)
+	}
+	test.wantNoInput = fmt.Sprintf(test.wantNoInput, ttype)
+	if *update {
+		if test.input != "" {
+			t.Logf("Updating %q", test.want)
+			input, err := os.ReadFile(test.input)
+			if err != nil {
+				t.Error(err)
+				return
+			}
+
+			f, err := os.Create(test.want)
+			if err != nil {
+				t.Error(err)
+				return
+			}
+			defer f.Close()
+			bw := newHuffmanBitWriter(f)
+			writeToType(t, ttype, bw, test.tokens, input)
+		}
+
+		t.Logf("Updating %q", test.wantNoInput)
+		f, err := os.Create(test.wantNoInput)
+		if err != nil {
+			t.Error(err)
+			return
+		}
+		defer f.Close()
+		bw := newHuffmanBitWriter(f)
+		writeToType(t, ttype, bw, test.tokens, nil)
+		return
+	}
+
+	if test.input != "" {
+		t.Logf("Testing %q", test.want)
+		input, err := os.ReadFile(test.input)
+		if err != nil {
+			t.Error(err)
+			return
+		}
+		want, err := os.ReadFile(test.want)
+		if err != nil {
+			t.Error(err)
+			return
+		}
+		var buf bytes.Buffer
+		bw := newHuffmanBitWriter(&buf)
+		writeToType(t, ttype, bw, test.tokens, input)
+
+		got := buf.Bytes()
+		if !bytes.Equal(got, want) {
+			t.Errorf("writeBlock did not yield expected result for file %q with input. See %q", test.want, test.want+".got")
+			if err := os.WriteFile(test.want+".got", got, 0666); err != nil {
+				t.Error(err)
+			}
+		}
+		t.Log("Output ok")
+
+		// Test if the writer produces the same output after reset.
+		buf.Reset()
+		bw.reset(&buf)
+		writeToType(t, ttype, bw, test.tokens, input)
+		bw.flush()
+		got = buf.Bytes()
+		if !bytes.Equal(got, want) {
+			t.Errorf("reset: writeBlock did not yield expected result for file %q with input. See %q", test.want, test.want+".reset.got")
+			if err := os.WriteFile(test.want+".reset.got", got, 0666); err != nil {
+				t.Error(err)
+			}
+			return
+		}
+		t.Log("Reset ok")
+		testWriterEOF(t, "wb", test, true)
+	}
+	t.Logf("Testing %q", test.wantNoInput)
+	wantNI, err := os.ReadFile(test.wantNoInput)
+	if err != nil {
+		t.Error(err)
+		return
+	}
+	var buf bytes.Buffer
+	bw := newHuffmanBitWriter(&buf)
+	writeToType(t, ttype, bw, test.tokens, nil)
+
+	got := buf.Bytes()
+	if !bytes.Equal(got, wantNI) {
+		t.Errorf("writeBlock did not yield expected result for file %q with input. See %q", test.wantNoInput, test.wantNoInput+".got")
+		if err := os.WriteFile(test.want+".got", got, 0666); err != nil {
+			t.Error(err)
+		}
+	} else if got[0]&1 == 1 {
+		t.Error("got unexpected EOF")
+		return
+	}
+
+	t.Log("Output ok")
+
+	// Test if the writer produces the same output after reset.
+	buf.Reset()
+	bw.reset(&buf)
+	writeToType(t, ttype, bw, test.tokens, nil)
+	bw.flush()
+	got = buf.Bytes()
+	if !bytes.Equal(got, wantNI) {
+		t.Errorf("reset: writeBlock did not yield expected result for file %q without input. See %q", test.want, test.want+".reset.got")
+		if err := os.WriteFile(test.want+".reset.got", got, 0666); err != nil {
+			t.Error(err)
+		}
+		return
+	}
+	t.Log("Reset ok")
+	testWriterEOF(t, "wb", test, false)
+}
+
+func writeToType(t *testing.T, ttype string, bw *huffmanBitWriter, tok []token, input []byte) {
+	switch ttype {
+	case "wb":
+		bw.writeBlock(tok, false, input)
+	case "dyn":
+		bw.writeBlockDynamic(tok, false, input)
+	default:
+		panic("unknown test type")
+	}
+
+	if bw.err != nil {
+		t.Error(bw.err)
+		return
+	}
+
+	bw.flush()
+	if bw.err != nil {
+		t.Error(bw.err)
+		return
+	}
+}
+
+// testWriterEOF tests if the written block contains an EOF marker.
+func testWriterEOF(t *testing.T, ttype string, test huffTest, useInput bool) {
+	if useInput && test.input == "" {
+		return
+	}
+	var input []byte
+	if useInput {
+		var err error
+		input, err = os.ReadFile(test.input)
+		if err != nil {
+			t.Error(err)
+			return
+		}
+	}
+	var buf bytes.Buffer
+	bw := newHuffmanBitWriter(&buf)
+	switch ttype {
+	case "wb":
+		bw.writeBlock(test.tokens, true, input)
+	case "dyn":
+		bw.writeBlockDynamic(test.tokens, true, input)
+	case "huff":
+		bw.writeBlockHuff(true, input)
+	default:
+		panic("unknown test type")
+	}
+	if bw.err != nil {
+		t.Error(bw.err)
+		return
+	}
+
+	bw.flush()
+	if bw.err != nil {
+		t.Error(bw.err)
+		return
+	}
+	b := buf.Bytes()
+	if len(b) == 0 {
+		t.Error("no output received")
+		return
+	}
+	if b[0]&1 != 1 {
+		t.Errorf("block not marked with EOF for input %q", test.input)
+		return
+	}
+	t.Log("EOF ok")
+}
diff --git a/src/compress/flate/huffman_code.go b/src/compress/flate/huffman_code.go
new file mode 100644
index 0000000..891537e
--- /dev/null
+++ b/src/compress/flate/huffman_code.go
@@ -0,0 +1,349 @@
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package flate
+
+import (
+	"math"
+	"math/bits"
+	"sort"
+)
+
+// hcode is a huffman code with a bit code and bit length.
+type hcode struct {
+	code, len uint16
+}
+
+type huffmanEncoder struct {
+	codes     []hcode
+	freqcache []literalNode
+	bitCount  [17]int32
+	lns       byLiteral // stored to avoid repeated allocation in generate
+	lfs       byFreq    // stored to avoid repeated allocation in generate
+}
+
+type literalNode struct {
+	literal uint16
+	freq    int32
+}
+
+// A levelInfo describes the state of the constructed tree for a given depth.
+type levelInfo struct {
+	// Our level.  for better printing
+	level int32
+
+	// The frequency of the last node at this level
+	lastFreq int32
+
+	// The frequency of the next character to add to this level
+	nextCharFreq int32
+
+	// The frequency of the next pair (from level below) to add to this level.
+	// Only valid if the "needed" value of the next lower level is 0.
+	nextPairFreq int32
+
+	// The number of chains remaining to generate for this level before moving
+	// up to the next level
+	needed int32
+}
+
+// set sets the code and length of an hcode.
+func (h *hcode) set(code uint16, length uint16) {
+	h.len = length
+	h.code = code
+}
+
+func maxNode() literalNode { return literalNode{math.MaxUint16, math.MaxInt32} }
+
+func newHuffmanEncoder(size int) *huffmanEncoder {
+	return &huffmanEncoder{codes: make([]hcode, size)}
+}
+
+// Generates a HuffmanCode corresponding to the fixed literal table
+func generateFixedLiteralEncoding() *huffmanEncoder {
+	h := newHuffmanEncoder(maxNumLit)
+	codes := h.codes
+	var ch uint16
+	for ch = 0; ch < maxNumLit; ch++ {
+		var bits uint16
+		var size uint16
+		switch {
+		case ch < 144:
+			// size 8, 000110000  .. 10111111
+			bits = ch + 48
+			size = 8
+			break
+		case ch < 256:
+			// size 9, 110010000 .. 111111111
+			bits = ch + 400 - 144
+			size = 9
+			break
+		case ch < 280:
+			// size 7, 0000000 .. 0010111
+			bits = ch - 256
+			size = 7
+			break
+		default:
+			// size 8, 11000000 .. 11000111
+			bits = ch + 192 - 280
+			size = 8
+		}
+		codes[ch] = hcode{code: reverseBits(bits, byte(size)), len: size}
+	}
+	return h
+}
+
+func generateFixedOffsetEncoding() *huffmanEncoder {
+	h := newHuffmanEncoder(30)
+	codes := h.codes
+	for ch := range codes {
+		codes[ch] = hcode{code: reverseBits(uint16(ch), 5), len: 5}
+	}
+	return h
+}
+
+var fixedLiteralEncoding *huffmanEncoder = generateFixedLiteralEncoding()
+var fixedOffsetEncoding *huffmanEncoder = generateFixedOffsetEncoding()
+
+func (h *huffmanEncoder) bitLength(freq []int32) int {
+	var total int
+	for i, f := range freq {
+		if f != 0 {
+			total += int(f) * int(h.codes[i].len)
+		}
+	}
+	return total
+}
+
+const maxBitsLimit = 16
+
+// Return the number of literals assigned to each bit size in the Huffman encoding
+//
+// This method is only called when list.length >= 3
+// The cases of 0, 1, and 2 literals are handled by special case code.
+//
+// list  An array of the literals with non-zero frequencies
+//             and their associated frequencies. The array is in order of increasing
+//             frequency, and has as its last element a special element with frequency
+//             MaxInt32
+// maxBits     The maximum number of bits that should be used to encode any literal.
+//             Must be less than 16.
+// return      An integer array in which array[i] indicates the number of literals
+//             that should be encoded in i bits.
+func (h *huffmanEncoder) bitCounts(list []literalNode, maxBits int32) []int32 {
+	if maxBits >= maxBitsLimit {
+		panic("flate: maxBits too large")
+	}
+	n := int32(len(list))
+	list = list[0 : n+1]
+	list[n] = maxNode()
+
+	// The tree can't have greater depth than n - 1, no matter what. This
+	// saves a little bit of work in some small cases
+	if maxBits > n-1 {
+		maxBits = n - 1
+	}
+
+	// Create information about each of the levels.
+	// A bogus "Level 0" whose sole purpose is so that
+	// level1.prev.needed==0.  This makes level1.nextPairFreq
+	// be a legitimate value that never gets chosen.
+	var levels [maxBitsLimit]levelInfo
+	// leafCounts[i] counts the number of literals at the left
+	// of ancestors of the rightmost node at level i.
+	// leafCounts[i][j] is the number of literals at the left
+	// of the level j ancestor.
+	var leafCounts [maxBitsLimit][maxBitsLimit]int32
+
+	for level := int32(1); level <= maxBits; level++ {
+		// For every level, the first two items are the first two characters.
+		// We initialize the levels as if we had already figured this out.
+		levels[level] = levelInfo{
+			level:        level,
+			lastFreq:     list[1].freq,
+			nextCharFreq: list[2].freq,
+			nextPairFreq: list[0].freq + list[1].freq,
+		}
+		leafCounts[level][level] = 2
+		if level == 1 {
+			levels[level].nextPairFreq = math.MaxInt32
+		}
+	}
+
+	// We need a total of 2*n - 2 items at top level and have already generated 2.
+	levels[maxBits].needed = 2*n - 4
+
+	level := maxBits
+	for {
+		l := &levels[level]
+		if l.nextPairFreq == math.MaxInt32 && l.nextCharFreq == math.MaxInt32 {
+			// We've run out of both leafs and pairs.
+			// End all calculations for this level.
+			// To make sure we never come back to this level or any lower level,
+			// set nextPairFreq impossibly large.
+			l.needed = 0
+			levels[level+1].nextPairFreq = math.MaxInt32
+			level++
+			continue
+		}
+
+		prevFreq := l.lastFreq
+		if l.nextCharFreq < l.nextPairFreq {
+			// The next item on this row is a leaf node.
+			n := leafCounts[level][level] + 1
+			l.lastFreq = l.nextCharFreq
+			// Lower leafCounts are the same of the previous node.
+			leafCounts[level][level] = n
+			l.nextCharFreq = list[n].freq
+		} else {
+			// The next item on this row is a pair from the previous row.
+			// nextPairFreq isn't valid until we generate two
+			// more values in the level below
+			l.lastFreq = l.nextPairFreq
+			// Take leaf counts from the lower level, except counts[level] remains the same.
+			copy(leafCounts[level][:level], leafCounts[level-1][:level])
+			levels[l.level-1].needed = 2
+		}
+
+		if l.needed--; l.needed == 0 {
+			// We've done everything we need to do for this level.
+			// Continue calculating one level up. Fill in nextPairFreq
+			// of that level with the sum of the two nodes we've just calculated on
+			// this level.
+			if l.level == maxBits {
+				// All done!
+				break
+			}
+			levels[l.level+1].nextPairFreq = prevFreq + l.lastFreq
+			level++
+		} else {
+			// If we stole from below, move down temporarily to replenish it.
+			for levels[level-1].needed > 0 {
+				level--
+			}
+		}
+	}
+
+	// Somethings is wrong if at the end, the top level is null or hasn't used
+	// all of the leaves.
+	if leafCounts[maxBits][maxBits] != n {
+		panic("leafCounts[maxBits][maxBits] != n")
+	}
+
+	bitCount := h.bitCount[:maxBits+1]
+	bits := 1
+	counts := &leafCounts[maxBits]
+	for level := maxBits; level > 0; level-- {
+		// chain.leafCount gives the number of literals requiring at least "bits"
+		// bits to encode.
+		bitCount[bits] = counts[level] - counts[level-1]
+		bits++
+	}
+	return bitCount
+}
+
+// Look at the leaves and assign them a bit count and an encoding as specified
+// in RFC 1951 3.2.2
+func (h *huffmanEncoder) assignEncodingAndSize(bitCount []int32, list []literalNode) {
+	code := uint16(0)
+	for n, bits := range bitCount {
+		code <<= 1
+		if n == 0 || bits == 0 {
+			continue
+		}
+		// The literals list[len(list)-bits] .. list[len(list)-bits]
+		// are encoded using "bits" bits, and get the values
+		// code, code + 1, ....  The code values are
+		// assigned in literal order (not frequency order).
+		chunk := list[len(list)-int(bits):]
+
+		h.lns.sort(chunk)
+		for _, node := range chunk {
+			h.codes[node.literal] = hcode{code: reverseBits(code, uint8(n)), len: uint16(n)}
+			code++
+		}
+		list = list[0 : len(list)-int(bits)]
+	}
+}
+
+// Update this Huffman Code object to be the minimum code for the specified frequency count.
+//
+// freq  An array of frequencies, in which frequency[i] gives the frequency of literal i.
+// maxBits  The maximum number of bits to use for any literal.
+func (h *huffmanEncoder) generate(freq []int32, maxBits int32) {
+	if h.freqcache == nil {
+		// Allocate a reusable buffer with the longest possible frequency table.
+		// Possible lengths are codegenCodeCount, offsetCodeCount and maxNumLit.
+		// The largest of these is maxNumLit, so we allocate for that case.
+		h.freqcache = make([]literalNode, maxNumLit+1)
+	}
+	list := h.freqcache[:len(freq)+1]
+	// Number of non-zero literals
+	count := 0
+	// Set list to be the set of all non-zero literals and their frequencies
+	for i, f := range freq {
+		if f != 0 {
+			list[count] = literalNode{uint16(i), f}
+			count++
+		} else {
+			list[count] = literalNode{}
+			h.codes[i].len = 0
+		}
+	}
+	list[len(freq)] = literalNode{}
+
+	list = list[:count]
+	if count <= 2 {
+		// Handle the small cases here, because they are awkward for the general case code. With
+		// two or fewer literals, everything has bit length 1.
+		for i, node := range list {
+			// "list" is in order of increasing literal value.
+			h.codes[node.literal].set(uint16(i), 1)
+		}
+		return
+	}
+	h.lfs.sort(list)
+
+	// Get the number of literals for each bit count
+	bitCount := h.bitCounts(list, maxBits)
+	// And do the assignment
+	h.assignEncodingAndSize(bitCount, list)
+}
+
+type byLiteral []literalNode
+
+func (s *byLiteral) sort(a []literalNode) {
+	*s = byLiteral(a)
+	sort.Sort(s)
+}
+
+func (s byLiteral) Len() int { return len(s) }
+
+func (s byLiteral) Less(i, j int) bool {
+	return s[i].literal < s[j].literal
+}
+
+func (s byLiteral) Swap(i, j int) { s[i], s[j] = s[j], s[i] }
+
+type byFreq []literalNode
+
+func (s *byFreq) sort(a []literalNode) {
+	*s = byFreq(a)
+	sort.Sort(s)
+}
+
+func (s byFreq) Len() int { return len(s) }
+
+func (s byFreq) Less(i, j int) bool {
+	if s[i].freq == s[j].freq {
+		return s[i].literal < s[j].literal
+	}
+	return s[i].freq < s[j].freq
+}
+
+func (s byFreq) Swap(i, j int) { s[i], s[j] = s[j], s[i] }
+
+func reverseBits(number uint16, bitLength byte) uint16 {
+	return bits.Reverse16(number << (16 - bitLength))
+}
diff --git a/src/compress/flate/inflate.go b/src/compress/flate/inflate.go
new file mode 100644
index 0000000..4992139
--- /dev/null
+++ b/src/compress/flate/inflate.go
@@ -0,0 +1,825 @@
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Package flate implements the DEFLATE compressed data format, described in
+// RFC 1951.  The gzip and zlib packages implement access to DEFLATE-based file
+// formats.
+package flate
+
+import (
+	"bufio"
+	"io"
+	"math/bits"
+	"strconv"
+	"sync"
+)
+
+const (
+	maxCodeLen = 16 // max length of Huffman code
+	// The next three numbers come from the RFC section 3.2.7, with the
+	// additional proviso in section 3.2.5 which implies that distance codes
+	// 30 and 31 should never occur in compressed data.
+	maxNumLit  = 286
+	maxNumDist = 30
+	numCodes   = 19 // number of codes in Huffman meta-code
+)
+
+// Initialize the fixedHuffmanDecoder only once upon first use.
+var fixedOnce sync.Once
+var fixedHuffmanDecoder huffmanDecoder
+
+// A CorruptInputError reports the presence of corrupt input at a given offset.
+type CorruptInputError int64
+
+func (e CorruptInputError) Error() string {
+	return "flate: corrupt input before offset " + strconv.FormatInt(int64(e), 10)
+}
+
+// An InternalError reports an error in the flate code itself.
+type InternalError string
+
+func (e InternalError) Error() string { return "flate: internal error: " + string(e) }
+
+// A ReadError reports an error encountered while reading input.
+//
+// Deprecated: No longer returned.
+type ReadError struct {
+	Offset int64 // byte offset where error occurred
+	Err    error // error returned by underlying Read
+}
+
+func (e *ReadError) Error() string {
+	return "flate: read error at offset " + strconv.FormatInt(e.Offset, 10) + ": " + e.Err.Error()
+}
+
+// A WriteError reports an error encountered while writing output.
+//
+// Deprecated: No longer returned.
+type WriteError struct {
+	Offset int64 // byte offset where error occurred
+	Err    error // error returned by underlying Write
+}
+
+func (e *WriteError) Error() string {
+	return "flate: write error at offset " + strconv.FormatInt(e.Offset, 10) + ": " + e.Err.Error()
+}
+
+// Resetter resets a ReadCloser returned by NewReader or NewReaderDict
+// to switch to a new underlying Reader. This permits reusing a ReadCloser
+// instead of allocating a new one.
+type Resetter interface {
+	// Reset discards any buffered data and resets the Resetter as if it was
+	// newly initialized with the given reader.
+	Reset(r io.Reader, dict []byte) error
+}
+
+// The data structure for decoding Huffman tables is based on that of
+// zlib. There is a lookup table of a fixed bit width (huffmanChunkBits),
+// For codes smaller than the table width, there are multiple entries
+// (each combination of trailing bits has the same value). For codes
+// larger than the table width, the table contains a link to an overflow
+// table. The width of each entry in the link table is the maximum code
+// size minus the chunk width.
+//
+// Note that you can do a lookup in the table even without all bits
+// filled. Since the extra bits are zero, and the DEFLATE Huffman codes
+// have the property that shorter codes come before longer ones, the
+// bit length estimate in the result is a lower bound on the actual
+// number of bits.
+//
+// See the following:
+//	https://github.com/madler/zlib/raw/master/doc/algorithm.txt
+
+// chunk & 15 is number of bits
+// chunk >> 4 is value, including table link
+
+const (
+	huffmanChunkBits  = 9
+	huffmanNumChunks  = 1 << huffmanChunkBits
+	huffmanCountMask  = 15
+	huffmanValueShift = 4
+)
+
+type huffmanDecoder struct {
+	min      int                      // the minimum code length
+	chunks   [huffmanNumChunks]uint32 // chunks as described above
+	links    [][]uint32               // overflow links
+	linkMask uint32                   // mask the width of the link table
+}
+
+// Initialize Huffman decoding tables from array of code lengths.
+// Following this function, h is guaranteed to be initialized into a complete
+// tree (i.e., neither over-subscribed nor under-subscribed). The exception is a
+// degenerate case where the tree has only a single symbol with length 1. Empty
+// trees are permitted.
+func (h *huffmanDecoder) init(lengths []int) bool {
+	// Sanity enables additional runtime tests during Huffman
+	// table construction. It's intended to be used during
+	// development to supplement the currently ad-hoc unit tests.
+	const sanity = false
+
+	if h.min != 0 {
+		*h = huffmanDecoder{}
+	}
+
+	// Count number of codes of each length,
+	// compute min and max length.
+	var count [maxCodeLen]int
+	var min, max int
+	for _, n := range lengths {
+		if n == 0 {
+			continue
+		}
+		if min == 0 || n < min {
+			min = n
+		}
+		if n > max {
+			max = n
+		}
+		count[n]++
+	}
+
+	// Empty tree. The decompressor.huffSym function will fail later if the tree
+	// is used. Technically, an empty tree is only valid for the HDIST tree and
+	// not the HCLEN and HLIT tree. However, a stream with an empty HCLEN tree
+	// is guaranteed to fail since it will attempt to use the tree to decode the
+	// codes for the HLIT and HDIST trees. Similarly, an empty HLIT tree is
+	// guaranteed to fail later since the compressed data section must be
+	// composed of at least one symbol (the end-of-block marker).
+	if max == 0 {
+		return true
+	}
+
+	code := 0
+	var nextcode [maxCodeLen]int
+	for i := min; i <= max; i++ {
+		code <<= 1
+		nextcode[i] = code
+		code += count[i]
+	}
+
+	// Check that the coding is complete (i.e., that we've
+	// assigned all 2-to-the-max possible bit sequences).
+	// Exception: To be compatible with zlib, we also need to
+	// accept degenerate single-code codings. See also
+	// TestDegenerateHuffmanCoding.
+	if code != 1<<uint(max) && !(code == 1 && max == 1) {
+		return false
+	}
+
+	h.min = min
+	if max > huffmanChunkBits {
+		numLinks := 1 << (uint(max) - huffmanChunkBits)
+		h.linkMask = uint32(numLinks - 1)
+
+		// create link tables
+		link := nextcode[huffmanChunkBits+1] >> 1
+		h.links = make([][]uint32, huffmanNumChunks-link)
+		for j := uint(link); j < huffmanNumChunks; j++ {
+			reverse := int(bits.Reverse16(uint16(j)))
+			reverse >>= uint(16 - huffmanChunkBits)
+			off := j - uint(link)
+			if sanity && h.chunks[reverse] != 0 {
+				panic("impossible: overwriting existing chunk")
+			}
+			h.chunks[reverse] = uint32(off<<huffmanValueShift | (huffmanChunkBits + 1))
+			h.links[off] = make([]uint32, numLinks)
+		}
+	}
+
+	for i, n := range lengths {
+		if n == 0 {
+			continue
+		}
+		code := nextcode[n]
+		nextcode[n]++
+		chunk := uint32(i<<huffmanValueShift | n)
+		reverse := int(bits.Reverse16(uint16(code)))
+		reverse >>= uint(16 - n)
+		if n <= huffmanChunkBits {
+			for off := reverse; off < len(h.chunks); off += 1 << uint(n) {
+				// We should never need to overwrite
+				// an existing chunk. Also, 0 is
+				// never a valid chunk, because the
+				// lower 4 "count" bits should be
+				// between 1 and 15.
+				if sanity && h.chunks[off] != 0 {
+					panic("impossible: overwriting existing chunk")
+				}
+				h.chunks[off] = chunk
+			}
+		} else {
+			j := reverse & (huffmanNumChunks - 1)
+			if sanity && h.chunks[j]&huffmanCountMask != huffmanChunkBits+1 {
+				// Longer codes should have been
+				// associated with a link table above.
+				panic("impossible: not an indirect chunk")
+			}
+			value := h.chunks[j] >> huffmanValueShift
+			linktab := h.links[value]
+			reverse >>= huffmanChunkBits
+			for off := reverse; off < len(linktab); off += 1 << uint(n-huffmanChunkBits) {
+				if sanity && linktab[off] != 0 {
+					panic("impossible: overwriting existing chunk")
+				}
+				linktab[off] = chunk
+			}
+		}
+	}
+
+	if sanity {
+		// Above we've sanity checked that we never overwrote
+		// an existing entry. Here we additionally check that
+		// we filled the tables completely.
+		for i, chunk := range h.chunks {
+			if chunk == 0 {
+				// As an exception, in the degenerate
+				// single-code case, we allow odd
+				// chunks to be missing.
+				if code == 1 && i%2 == 1 {
+					continue
+				}
+				panic("impossible: missing chunk")
+			}
+		}
+		for _, linktab := range h.links {
+			for _, chunk := range linktab {
+				if chunk == 0 {
+					panic("impossible: missing chunk")
+				}
+			}
+		}
+	}
+
+	return true
+}
+
+// The actual read interface needed by NewReader.
+// If the passed in io.Reader does not also have ReadByte,
+// the NewReader will introduce its own buffering.
+type Reader interface {
+	io.Reader
+	io.ByteReader
+}
+
+// Decompress state.
+type decompressor struct {
+	// Input source.
+	r       Reader
+	roffset int64
+
+	// Input bits, in top of b.
+	b  uint32
+	nb uint
+
+	// Huffman decoders for literal/length, distance.
+	h1, h2 huffmanDecoder
+
+	// Length arrays used to define Huffman codes.
+	bits     *[maxNumLit + maxNumDist]int
+	codebits *[numCodes]int
+
+	// Output history, buffer.
+	dict dictDecoder
+
+	// Temporary buffer (avoids repeated allocation).
+	buf [4]byte
+
+	// Next step in the decompression,
+	// and decompression state.
+	step      func(*decompressor)
+	stepState int
+	final     bool
+	err       error
+	toRead    []byte
+	hl, hd    *huffmanDecoder
+	copyLen   int
+	copyDist  int
+}
+
+func (f *decompressor) nextBlock() {
+	for f.nb < 1+2 {
+		if f.err = f.moreBits(); f.err != nil {
+			return
+		}
+	}
+	f.final = f.b&1 == 1
+	f.b >>= 1
+	typ := f.b & 3
+	f.b >>= 2
+	f.nb -= 1 + 2
+	switch typ {
+	case 0:
+		f.dataBlock()
+	case 1:
+		// compressed, fixed Huffman tables
+		f.hl = &fixedHuffmanDecoder
+		f.hd = nil
+		f.huffmanBlock()
+	case 2:
+		// compressed, dynamic Huffman tables
+		if f.err = f.readHuffman(); f.err != nil {
+			break
+		}
+		f.hl = &f.h1
+		f.hd = &f.h2
+		f.huffmanBlock()
+	default:
+		// 3 is reserved.
+		f.err = CorruptInputError(f.roffset)
+	}
+}
+
+func (f *decompressor) Read(b []byte) (int, error) {
+	for {
+		if len(f.toRead) > 0 {
+			n := copy(b, f.toRead)
+			f.toRead = f.toRead[n:]
+			if len(f.toRead) == 0 {
+				return n, f.err
+			}
+			return n, nil
+		}
+		if f.err != nil {
+			return 0, f.err
+		}
+		f.step(f)
+		if f.err != nil && len(f.toRead) == 0 {
+			f.toRead = f.dict.readFlush() // Flush what's left in case of error
+		}
+	}
+}
+
+func (f *decompressor) Close() error {
+	if f.err == io.EOF {
+		return nil
+	}
+	return f.err
+}
+
+// RFC 1951 section 3.2.7.
+// Compression with dynamic Huffman codes
+
+var codeOrder = [...]int{16, 17, 18, 0, 8, 7, 9, 6, 10, 5, 11, 4, 12, 3, 13, 2, 14, 1, 15}
+
+func (f *decompressor) readHuffman() error {
+	// HLIT[5], HDIST[5], HCLEN[4].
+	for f.nb < 5+5+4 {
+		if err := f.moreBits(); err != nil {
+			return err
+		}
+	}
+	nlit := int(f.b&0x1F) + 257
+	if nlit > maxNumLit {
+		return CorruptInputError(f.roffset)
+	}
+	f.b >>= 5
+	ndist := int(f.b&0x1F) + 1
+	if ndist > maxNumDist {
+		return CorruptInputError(f.roffset)
+	}
+	f.b >>= 5
+	nclen := int(f.b&0xF) + 4
+	// numCodes is 19, so nclen is always valid.
+	f.b >>= 4
+	f.nb -= 5 + 5 + 4
+
+	// (HCLEN+4)*3 bits: code lengths in the magic codeOrder order.
+	for i := 0; i < nclen; i++ {
+		for f.nb < 3 {
+			if err := f.moreBits(); err != nil {
+				return err
+			}
+		}
+		f.codebits[codeOrder[i]] = int(f.b & 0x7)
+		f.b >>= 3
+		f.nb -= 3
+	}
+	for i := nclen; i < len(codeOrder); i++ {
+		f.codebits[codeOrder[i]] = 0
+	}
+	if !f.h1.init(f.codebits[0:]) {
+		return CorruptInputError(f.roffset)
+	}
+
+	// HLIT + 257 code lengths, HDIST + 1 code lengths,
+	// using the code length Huffman code.
+	for i, n := 0, nlit+ndist; i < n; {
+		x, err := f.huffSym(&f.h1)
+		if err != nil {
+			return err
+		}
+		if x < 16 {
+			// Actual length.
+			f.bits[i] = x
+			i++
+			continue
+		}
+		// Repeat previous length or zero.
+		var rep int
+		var nb uint
+		var b int
+		switch x {
+		default:
+			return InternalError("unexpected length code")
+		case 16:
+			rep = 3
+			nb = 2
+			if i == 0 {
+				return CorruptInputError(f.roffset)
+			}
+			b = f.bits[i-1]
+		case 17:
+			rep = 3
+			nb = 3
+			b = 0
+		case 18:
+			rep = 11
+			nb = 7
+			b = 0
+		}
+		for f.nb < nb {
+			if err := f.moreBits(); err != nil {
+				return err
+			}
+		}
+		rep += int(f.b & uint32(1<<nb-1))
+		f.b >>= nb
+		f.nb -= nb
+		if i+rep > n {
+			return CorruptInputError(f.roffset)
+		}
+		for j := 0; j < rep; j++ {
+			f.bits[i] = b
+			i++
+		}
+	}
+
+	if !f.h1.init(f.bits[0:nlit]) || !f.h2.init(f.bits[nlit:nlit+ndist]) {
+		return CorruptInputError(f.roffset)
+	}
+
+	// As an optimization, we can initialize the min bits to read at a time
+	// for the HLIT tree to the length of the EOB marker since we know that
+	// every block must terminate with one. This preserves the property that
+	// we never read any extra bytes after the end of the DEFLATE stream.
+	if f.h1.min < f.bits[endBlockMarker] {
+		f.h1.min = f.bits[endBlockMarker]
+	}
+
+	return nil
+}
+
+// Decode a single Huffman block from f.
+// hl and hd are the Huffman states for the lit/length values
+// and the distance values, respectively. If hd == nil, using the
+// fixed distance encoding associated with fixed Huffman blocks.
+func (f *decompressor) huffmanBlock() {
+	const (
+		stateInit = iota // Zero value must be stateInit
+		stateDict
+	)
+
+	switch f.stepState {
+	case stateInit:
+		goto readLiteral
+	case stateDict:
+		goto copyHistory
+	}
+
+readLiteral:
+	// Read literal and/or (length, distance) according to RFC section 3.2.3.
+	{
+		v, err := f.huffSym(f.hl)
+		if err != nil {
+			f.err = err
+			return
+		}
+		var n uint // number of bits extra
+		var length int
+		switch {
+		case v < 256:
+			f.dict.writeByte(byte(v))
+			if f.dict.availWrite() == 0 {
+				f.toRead = f.dict.readFlush()
+				f.step = (*decompressor).huffmanBlock
+				f.stepState = stateInit
+				return
+			}
+			goto readLiteral
+		case v == 256:
+			f.finishBlock()
+			return
+		// otherwise, reference to older data
+		case v < 265:
+			length = v - (257 - 3)
+			n = 0
+		case v < 269:
+			length = v*2 - (265*2 - 11)
+			n = 1
+		case v < 273:
+			length = v*4 - (269*4 - 19)
+			n = 2
+		case v < 277:
+			length = v*8 - (273*8 - 35)
+			n = 3
+		case v < 281:
+			length = v*16 - (277*16 - 67)
+			n = 4
+		case v < 285:
+			length = v*32 - (281*32 - 131)
+			n = 5
+		case v < maxNumLit:
+			length = 258
+			n = 0
+		default:
+			f.err = CorruptInputError(f.roffset)
+			return
+		}
+		if n > 0 {
+			for f.nb < n {
+				if err = f.moreBits(); err != nil {
+					f.err = err
+					return
+				}
+			}
+			length += int(f.b & uint32(1<<n-1))
+			f.b >>= n
+			f.nb -= n
+		}
+
+		var dist int
+		if f.hd == nil {
+			for f.nb < 5 {
+				if err = f.moreBits(); err != nil {
+					f.err = err
+					return
+				}
+			}
+			dist = int(bits.Reverse8(uint8(f.b & 0x1F << 3)))
+			f.b >>= 5
+			f.nb -= 5
+		} else {
+			if dist, err = f.huffSym(f.hd); err != nil {
+				f.err = err
+				return
+			}
+		}
+
+		switch {
+		case dist < 4:
+			dist++
+		case dist < maxNumDist:
+			nb := uint(dist-2) >> 1
+			// have 1 bit in bottom of dist, need nb more.
+			extra := (dist & 1) << nb
+			for f.nb < nb {
+				if err = f.moreBits(); err != nil {
+					f.err = err
+					return
+				}
+			}
+			extra |= int(f.b & uint32(1<<nb-1))
+			f.b >>= nb
+			f.nb -= nb
+			dist = 1<<(nb+1) + 1 + extra
+		default:
+			f.err = CorruptInputError(f.roffset)
+			return
+		}
+
+		// No check on length; encoding can be prescient.
+		if dist > f.dict.histSize() {
+			f.err = CorruptInputError(f.roffset)
+			return
+		}
+
+		f.copyLen, f.copyDist = length, dist
+		goto copyHistory
+	}
+
+copyHistory:
+	// Perform a backwards copy according to RFC section 3.2.3.
+	{
+		cnt := f.dict.tryWriteCopy(f.copyDist, f.copyLen)
+		if cnt == 0 {
+			cnt = f.dict.writeCopy(f.copyDist, f.copyLen)
+		}
+		f.copyLen -= cnt
+
+		if f.dict.availWrite() == 0 || f.copyLen > 0 {
+			f.toRead = f.dict.readFlush()
+			f.step = (*decompressor).huffmanBlock // We need to continue this work
+			f.stepState = stateDict
+			return
+		}
+		goto readLiteral
+	}
+}
+
+// Copy a single uncompressed data block from input to output.
+func (f *decompressor) dataBlock() {
+	// Uncompressed.
+	// Discard current half-byte.
+	f.nb = 0
+	f.b = 0
+
+	// Length then ones-complement of length.
+	nr, err := io.ReadFull(f.r, f.buf[0:4])
+	f.roffset += int64(nr)
+	if err != nil {
+		f.err = noEOF(err)
+		return
+	}
+	n := int(f.buf[0]) | int(f.buf[1])<<8
+	nn := int(f.buf[2]) | int(f.buf[3])<<8
+	if uint16(nn) != uint16(^n) {
+		f.err = CorruptInputError(f.roffset)
+		return
+	}
+
+	if n == 0 {
+		f.toRead = f.dict.readFlush()
+		f.finishBlock()
+		return
+	}
+
+	f.copyLen = n
+	f.copyData()
+}
+
+// copyData copies f.copyLen bytes from the underlying reader into f.hist.
+// It pauses for reads when f.hist is full.
+func (f *decompressor) copyData() {
+	buf := f.dict.writeSlice()
+	if len(buf) > f.copyLen {
+		buf = buf[:f.copyLen]
+	}
+
+	cnt, err := io.ReadFull(f.r, buf)
+	f.roffset += int64(cnt)
+	f.copyLen -= cnt
+	f.dict.writeMark(cnt)
+	if err != nil {
+		f.err = noEOF(err)
+		return
+	}
+
+	if f.dict.availWrite() == 0 || f.copyLen > 0 {
+		f.toRead = f.dict.readFlush()
+		f.step = (*decompressor).copyData
+		return
+	}
+	f.finishBlock()
+}
+
+func (f *decompressor) finishBlock() {
+	if f.final {
+		if f.dict.availRead() > 0 {
+			f.toRead = f.dict.readFlush()
+		}
+		f.err = io.EOF
+	}
+	f.step = (*decompressor).nextBlock
+}
+
+// noEOF returns err, unless err == io.EOF, in which case it returns io.ErrUnexpectedEOF.
+func noEOF(e error) error {
+	if e == io.EOF {
+		return io.ErrUnexpectedEOF
+	}
+	return e
+}
+
+func (f *decompressor) moreBits() error {
+	c, err := f.r.ReadByte()
+	if err != nil {
+		return noEOF(err)
+	}
+	f.roffset++
+	f.b |= uint32(c) << f.nb
+	f.nb += 8
+	return nil
+}
+
+// Read the next Huffman-encoded symbol from f according to h.
+func (f *decompressor) huffSym(h *huffmanDecoder) (int, error) {
+	// Since a huffmanDecoder can be empty or be composed of a degenerate tree
+	// with single element, huffSym must error on these two edge cases. In both
+	// cases, the chunks slice will be 0 for the invalid sequence, leading it
+	// satisfy the n == 0 check below.
+	n := uint(h.min)
+	// Optimization. Compiler isn't smart enough to keep f.b,f.nb in registers,
+	// but is smart enough to keep local variables in registers, so use nb and b,
+	// inline call to moreBits and reassign b,nb back to f on return.
+	nb, b := f.nb, f.b
+	for {
+		for nb < n {
+			c, err := f.r.ReadByte()
+			if err != nil {
+				f.b = b
+				f.nb = nb
+				return 0, noEOF(err)
+			}
+			f.roffset++
+			b |= uint32(c) << (nb & 31)
+			nb += 8
+		}
+		chunk := h.chunks[b&(huffmanNumChunks-1)]
+		n = uint(chunk & huffmanCountMask)
+		if n > huffmanChunkBits {
+			chunk = h.links[chunk>>huffmanValueShift][(b>>huffmanChunkBits)&h.linkMask]
+			n = uint(chunk & huffmanCountMask)
+		}
+		if n <= nb {
+			if n == 0 {
+				f.b = b
+				f.nb = nb
+				f.err = CorruptInputError(f.roffset)
+				return 0, f.err
+			}
+			f.b = b >> (n & 31)
+			f.nb = nb - n
+			return int(chunk >> huffmanValueShift), nil
+		}
+	}
+}
+
+func makeReader(r io.Reader) Reader {
+	if rr, ok := r.(Reader); ok {
+		return rr
+	}
+	return bufio.NewReader(r)
+}
+
+func fixedHuffmanDecoderInit() {
+	fixedOnce.Do(func() {
+		// These come from the RFC section 3.2.6.
+		var bits [288]int
+		for i := 0; i < 144; i++ {
+			bits[i] = 8
+		}
+		for i := 144; i < 256; i++ {
+			bits[i] = 9
+		}
+		for i := 256; i < 280; i++ {
+			bits[i] = 7
+		}
+		for i := 280; i < 288; i++ {
+			bits[i] = 8
+		}
+		fixedHuffmanDecoder.init(bits[:])
+	})
+}
+
+func (f *decompressor) Reset(r io.Reader, dict []byte) error {
+	*f = decompressor{
+		r:        makeReader(r),
+		bits:     f.bits,
+		codebits: f.codebits,
+		dict:     f.dict,
+		step:     (*decompressor).nextBlock,
+	}
+	f.dict.init(maxMatchOffset, dict)
+	return nil
+}
+
+// NewReader returns a new ReadCloser that can be used
+// to read the uncompressed version of r.
+// If r does not also implement io.ByteReader,
+// the decompressor may read more data than necessary from r.
+// It is the caller's responsibility to call Close on the ReadCloser
+// when finished reading.
+//
+// The ReadCloser returned by NewReader also implements Resetter.
+func NewReader(r io.Reader) io.ReadCloser {
+	fixedHuffmanDecoderInit()
+
+	var f decompressor
+	f.r = makeReader(r)
+	f.bits = new([maxNumLit + maxNumDist]int)
+	f.codebits = new([numCodes]int)
+	f.step = (*decompressor).nextBlock
+	f.dict.init(maxMatchOffset, nil)
+	return &f
+}
+
+// NewReaderDict is like NewReader but initializes the reader
+// with a preset dictionary. The returned Reader behaves as if
+// the uncompressed data stream started with the given dictionary,
+// which has already been read. NewReaderDict is typically used
+// to read data compressed by NewWriterDict.
+//
+// The ReadCloser returned by NewReader also implements Resetter.
+func NewReaderDict(r io.Reader, dict []byte) io.ReadCloser {
+	fixedHuffmanDecoderInit()
+
+	var f decompressor
+	f.r = makeReader(r)
+	f.bits = new([maxNumLit + maxNumDist]int)
+	f.codebits = new([numCodes]int)
+	f.step = (*decompressor).nextBlock
+	f.dict.init(maxMatchOffset, dict)
+	return &f
+}
diff --git a/src/compress/flate/inflate_test.go b/src/compress/flate/inflate_test.go
new file mode 100644
index 0000000..9575be1
--- /dev/null
+++ b/src/compress/flate/inflate_test.go
@@ -0,0 +1,97 @@
+// Copyright 2014 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package flate
+
+import (
+	"bytes"
+	"io"
+	"strings"
+	"testing"
+)
+
+func TestReset(t *testing.T) {
+	ss := []string{
+		"lorem ipsum izzle fo rizzle",
+		"the quick brown fox jumped over",
+	}
+
+	deflated := make([]bytes.Buffer, 2)
+	for i, s := range ss {
+		w, _ := NewWriter(&deflated[i], 1)
+		w.Write([]byte(s))
+		w.Close()
+	}
+
+	inflated := make([]bytes.Buffer, 2)
+
+	f := NewReader(&deflated[0])
+	io.Copy(&inflated[0], f)
+	f.(Resetter).Reset(&deflated[1], nil)
+	io.Copy(&inflated[1], f)
+	f.Close()
+
+	for i, s := range ss {
+		if s != inflated[i].String() {
+			t.Errorf("inflated[%d]:\ngot  %q\nwant %q", i, inflated[i], s)
+		}
+	}
+}
+
+func TestReaderTruncated(t *testing.T) {
+	vectors := []struct{ input, output string }{
+		{"\x00", ""},
+		{"\x00\f", ""},
+		{"\x00\f\x00", ""},
+		{"\x00\f\x00\xf3\xff", ""},
+		{"\x00\f\x00\xf3\xffhello", "hello"},
+		{"\x00\f\x00\xf3\xffhello, world", "hello, world"},
+		{"\x02", ""},
+		{"\xf2H\xcd", "He"},
+		{"\xf2H͙0a\u0084\t", "Hel\x90\x90\x90\x90\x90"},
+		{"\xf2H͙0a\u0084\t\x00", "Hel\x90\x90\x90\x90\x90"},
+	}
+
+	for i, v := range vectors {
+		r := strings.NewReader(v.input)
+		zr := NewReader(r)
+		b, err := io.ReadAll(zr)
+		if err != io.ErrUnexpectedEOF {
+			t.Errorf("test %d, error mismatch: got %v, want io.ErrUnexpectedEOF", i, err)
+		}
+		if string(b) != v.output {
+			t.Errorf("test %d, output mismatch: got %q, want %q", i, b, v.output)
+		}
+	}
+}
+
+func TestResetDict(t *testing.T) {
+	dict := []byte("the lorem fox")
+	ss := []string{
+		"lorem ipsum izzle fo rizzle",
+		"the quick brown fox jumped over",
+	}
+
+	deflated := make([]bytes.Buffer, len(ss))
+	for i, s := range ss {
+		w, _ := NewWriterDict(&deflated[i], DefaultCompression, dict)
+		w.Write([]byte(s))
+		w.Close()
+	}
+
+	inflated := make([]bytes.Buffer, len(ss))
+
+	f := NewReader(nil)
+	for i := range inflated {
+		f.(Resetter).Reset(&deflated[i], dict)
+		io.Copy(&inflated[i], f)
+	}
+	f.Close()
+
+	for i, s := range ss {
+		if s != inflated[i].String() {
+			t.Errorf("inflated[%d]:\ngot  %q\nwant %q", i, inflated[i], s)
+		}
+	}
+}
diff --git a/src/compress/flate/reader_test.go b/src/compress/flate/reader_test.go
new file mode 100644
index 0000000..94610fb
--- /dev/null
+++ b/src/compress/flate/reader_test.go
@@ -0,0 +1,98 @@
+// Copyright 2012 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package flate
+
+import (
+	"bytes"
+	"io"
+	"os"
+	"runtime"
+	"strings"
+	"testing"
+)
+
+func TestNlitOutOfRange(t *testing.T) {
+	// Trying to decode this bogus flate data, which has a Huffman table
+	// with nlit=288, should not panic.
+	io.Copy(io.Discard, NewReader(strings.NewReader(
+		"\xfc\xfe\x36\xe7\x5e\x1c\xef\xb3\x55\x58\x77\xb6\x56\xb5\x43\xf4"+
+			"\x6f\xf2\xd2\xe6\x3d\x99\xa0\x85\x8c\x48\xeb\xf8\xda\x83\x04\x2a"+
+			"\x75\xc4\xf8\x0f\x12\x11\xb9\xb4\x4b\x09\xa0\xbe\x8b\x91\x4c")))
+}
+
+var suites = []struct{ name, file string }{
+	// Digits is the digits of the irrational number e. Its decimal representation
+	// does not repeat, but there are only 10 possible digits, so it should be
+	// reasonably compressible.
+	{"Digits", "../testdata/e.txt"},
+	// Newton is Isaac Newtons's educational text on Opticks.
+	{"Newton", "../../testdata/Isaac.Newton-Opticks.txt"},
+}
+
+func BenchmarkDecode(b *testing.B) {
+	doBench(b, func(b *testing.B, buf0 []byte, level, n int) {
+		b.ReportAllocs()
+		b.StopTimer()
+		b.SetBytes(int64(n))
+
+		compressed := new(bytes.Buffer)
+		w, err := NewWriter(compressed, level)
+		if err != nil {
+			b.Fatal(err)
+		}
+		for i := 0; i < n; i += len(buf0) {
+			if len(buf0) > n-i {
+				buf0 = buf0[:n-i]
+			}
+			io.Copy(w, bytes.NewReader(buf0))
+		}
+		w.Close()
+		buf1 := compressed.Bytes()
+		buf0, compressed, w = nil, nil, nil
+		runtime.GC()
+		b.StartTimer()
+		for i := 0; i < b.N; i++ {
+			io.Copy(io.Discard, NewReader(bytes.NewReader(buf1)))
+		}
+	})
+}
+
+var levelTests = []struct {
+	name  string
+	level int
+}{
+	{"Huffman", HuffmanOnly},
+	{"Speed", BestSpeed},
+	{"Default", DefaultCompression},
+	{"Compression", BestCompression},
+}
+
+var sizes = []struct {
+	name string
+	n    int
+}{
+	{"1e4", 1e4},
+	{"1e5", 1e5},
+	{"1e6", 1e6},
+}
+
+func doBench(b *testing.B, f func(b *testing.B, buf []byte, level, n int)) {
+	for _, suite := range suites {
+		buf, err := os.ReadFile(suite.file)
+		if err != nil {
+			b.Fatal(err)
+		}
+		if len(buf) == 0 {
+			b.Fatalf("test file %q has no data", suite.file)
+		}
+		for _, l := range levelTests {
+			for _, s := range sizes {
+				b.Run(suite.name+"/"+l.name+"/"+s.name, func(b *testing.B) {
+					f(b, buf, l.level, s.n)
+				})
+			}
+		}
+	}
+}
diff --git a/src/compress/flate/testdata/huffman-null-max.dyn.expect b/src/compress/flate/testdata/huffman-null-max.dyn.expect
new file mode 100644
index 0000000..c081651
--- /dev/null
+++ b/src/compress/flate/testdata/huffman-null-max.dyn.expect
diff --git a/src/compress/flate/testdata/huffman-null-max.dyn.expect-noinput b/src/compress/flate/testdata/huffman-null-max.dyn.expect-noinput
new file mode 100644
index 0000000..c081651
--- /dev/null
+++ b/src/compress/flate/testdata/huffman-null-max.dyn.expect-noinput
diff --git a/src/compress/flate/testdata/huffman-null-max.golden b/src/compress/flate/testdata/huffman-null-max.golden
new file mode 100644
index 0000000..db422ca
--- /dev/null
+++ b/src/compress/flate/testdata/huffman-null-max.golden
diff --git a/src/compress/flate/testdata/huffman-null-max.in b/src/compress/flate/testdata/huffman-null-max.in
new file mode 100644
index 0000000..5dfddf0
--- /dev/null
+++ b/src/compress/flate/testdata/huffman-null-max.in
diff --git a/src/compress/flate/testdata/huffman-null-max.wb.expect b/src/compress/flate/testdata/huffman-null-max.wb.expect
new file mode 100644
index 0000000..c081651
--- /dev/null
+++ b/src/compress/flate/testdata/huffman-null-max.wb.expect
diff --git a/src/compress/flate/testdata/huffman-null-max.wb.expect-noinput b/src/compress/flate/testdata/huffman-null-max.wb.expect-noinput
new file mode 100644
index 0000000..c081651
--- /dev/null
+++ b/src/compress/flate/testdata/huffman-null-max.wb.expect-noinput
diff --git a/src/compress/flate/testdata/huffman-pi.dyn.expect b/src/compress/flate/testdata/huffman-pi.dyn.expect
new file mode 100644
index 0000000..e4396ac
--- /dev/null
+++ b/src/compress/flate/testdata/huffman-pi.dyn.expect
diff --git a/src/compress/flate/testdata/huffman-pi.dyn.expect-noinput b/src/compress/flate/testdata/huffman-pi.dyn.expect-noinput
new file mode 100644
index 0000000..e4396ac
--- /dev/null
+++ b/src/compress/flate/testdata/huffman-pi.dyn.expect-noinput
diff --git a/src/compress/flate/testdata/huffman-pi.golden b/src/compress/flate/testdata/huffman-pi.golden
new file mode 100644
index 0000000..23d8f7f
--- /dev/null
+++ b/src/compress/flate/testdata/huffman-pi.golden
diff --git a/src/compress/flate/testdata/huffman-pi.in b/src/compress/flate/testdata/huffman-pi.in
new file mode 100644
index 0000000..efaed43
--- /dev/null
+++ b/src/compress/flate/testdata/huffman-pi.in
@@ -0,0 +1 @@
+3.141592653589793238462643383279502884197169399375105820974944592307816406286208998628034825342117067982148086513282306647093844609550582231725359408128481117450284102701938521105559644622948954930381964428810975665933446128475648233786783165271201909145648566923460348610454326648213393607260249141273724587006606315588174881520920962829254091715364367892590360011330530548820466521384146951941511609433057270365759591953092186117381932611793105118548074462379962749567351885752724891227938183011949129833673362440656643086021394946395224737190702179860943702770539217176293176752384674818467669405132000568127145263560827785771342757789609173637178721468440901224953430146549585371050792279689258923542019956112129021960864034418159813629774771309960518707211349999998372978049951059731732816096318595024459455346908302642522308253344685035261931188171010003137838752886587533208381420617177669147303598253490428755468731159562863882353787593751957781857780532171226806613001927876611195909216420198938095257201065485863278865936153381827968230301952035301852968995773622599413891249721775283479131515574857242454150695950829533116861727855889075098381754637464939319255060400927701671139009848824012858361603563707660104710181942955596198946767837449448255379774726847104047534646208046684259069491293313677028989152104752162056966024058038150193511253382430035587640247496473263914199272604269922796782354781636009341721641219924586315030286182974555706749838505494588586926995690927210797509302955321165344987202755960236480665499119881834797753566369807426542527862551818417574672890977772793800081647060016145249192173217214772350141441973568548161361157352552133475741849468438523323907394143334547762416862518983569485562099219222184272550254256887671790494601653466804988627232791786085784383827967976681454100953883786360950680064225125205117392984896084128488626945604241965285022210661186306744278622039194945047123713786960956364371917287467764657573962413890865832645995813390478027590099465764078951269468398352595709825822620522489407726719478268482601476990902640136394437455305068203496252451749399651431429809190659250937221696461515709858387410597885959772975498930161753928468138268683868942774155991855925245953959431049972524680845987273644695848653836736222626099124608051243884390451244136549762780797715691435997700129616089441694868555848406353422072225828488648158456028506016842739452267467678895252138522549954666727823986456596116354886230577456498035593634568174324112515076069479451096596094025228879710893145669136867228748940560101503308617928680920874760917824938589009714909675985261365549781893129784821682998948722658804857564014270477555132379641451523746234364542858444795265867821051141354735739523113427166102135969536231442952484937187110145765403590279934403742007310578539062198387447808478489683321445713868751943506430218453191048481005370614680674919278191197939952061419663428754440643745123718192179998391015919561814675142691239748940907186494231961567945208095146550225231603881930142093762137855956638937787083039069792077346722182562599661501421503068038447734549202605414665925201497442850732518666002132434088190710486331734649651453905796268561005508106658796998163574736384052571459102897064140110971206280439039759515677157700420337869936007230558763176359421873125147120532928191826186125867321579198414848829164470609575270695722091756711672291098169091528017350671274858322287183520935396572512108357915136988209144421006751033467110314126711136990865851639831501970165151168517143765761835155650884909989859982387345528331635507647918535893226185489632132933089857064204675259070915481416549859461637180
\ No newline at end of file
diff --git a/src/compress/flate/testdata/huffman-pi.wb.expect b/src/compress/flate/testdata/huffman-pi.wb.expect
new file mode 100644
index 0000000..e4396ac
--- /dev/null
+++ b/src/compress/flate/testdata/huffman-pi.wb.expect
diff --git a/src/compress/flate/testdata/huffman-pi.wb.expect-noinput b/src/compress/flate/testdata/huffman-pi.wb.expect-noinput
new file mode 100644
index 0000000..e4396ac
--- /dev/null
+++ b/src/compress/flate/testdata/huffman-pi.wb.expect-noinput
diff --git a/src/compress/flate/testdata/huffman-rand-1k.dyn.expect b/src/compress/flate/testdata/huffman-rand-1k.dyn.expect
new file mode 100644
index 0000000..09dc798
--- /dev/null
+++ b/src/compress/flate/testdata/huffman-rand-1k.dyn.expect
diff --git a/src/compress/flate/testdata/huffman-rand-1k.dyn.expect-noinput b/src/compress/flate/testdata/huffman-rand-1k.dyn.expect-noinput
new file mode 100644
index 0000000..0c24742
--- /dev/null
+++ b/src/compress/flate/testdata/huffman-rand-1k.dyn.expect-noinput
diff --git a/src/compress/flate/testdata/huffman-rand-1k.golden b/src/compress/flate/testdata/huffman-rand-1k.golden
new file mode 100644
index 0000000..09dc798
--- /dev/null
+++ b/src/compress/flate/testdata/huffman-rand-1k.golden
diff --git a/src/compress/flate/testdata/huffman-rand-1k.in b/src/compress/flate/testdata/huffman-rand-1k.in
new file mode 100644
index 0000000..ce038eb
--- /dev/null
+++ b/src/compress/flate/testdata/huffman-rand-1k.in
diff --git a/src/compress/flate/testdata/huffman-rand-1k.wb.expect b/src/compress/flate/testdata/huffman-rand-1k.wb.expect
new file mode 100644
index 0000000..09dc798
--- /dev/null
+++ b/src/compress/flate/testdata/huffman-rand-1k.wb.expect
diff --git a/src/compress/flate/testdata/huffman-rand-1k.wb.expect-noinput b/src/compress/flate/testdata/huffman-rand-1k.wb.expect-noinput
new file mode 100644
index 0000000..0c24742
--- /dev/null
+++ b/src/compress/flate/testdata/huffman-rand-1k.wb.expect-noinput
diff --git a/src/compress/flate/testdata/huffman-rand-limit.dyn.expect b/src/compress/flate/testdata/huffman-rand-limit.dyn.expect
new file mode 100644
index 0000000..2d65279
--- /dev/null
+++ b/src/compress/flate/testdata/huffman-rand-limit.dyn.expect
diff --git a/src/compress/flate/testdata/huffman-rand-limit.dyn.expect-noinput b/src/compress/flate/testdata/huffman-rand-limit.dyn.expect-noinput
new file mode 100644
index 0000000..2d65279
--- /dev/null
+++ b/src/compress/flate/testdata/huffman-rand-limit.dyn.expect-noinput
diff --git a/src/compress/flate/testdata/huffman-rand-limit.golden b/src/compress/flate/testdata/huffman-rand-limit.golden
new file mode 100644
index 0000000..57e5932
--- /dev/null
+++ b/src/compress/flate/testdata/huffman-rand-limit.golden
diff --git a/src/compress/flate/testdata/huffman-rand-limit.in b/src/compress/flate/testdata/huffman-rand-limit.in
new file mode 100644
index 0000000..fb5b1be
--- /dev/null
+++ b/src/compress/flate/testdata/huffman-rand-limit.in
@@ -0,0 +1,4 @@
+aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
+���vH
+��%������ ��ɷ���}��>���ls���m�IGH���1Y�4�[��	0ˆ[|]o#�
+�-#���ul���pf��ٱ�n�Y�ԀY�w�C8ɯ02� F=gn�r�N!O���{����k�*�w(��b� ��kQC9/��
lu>�5�C.��u��
diff --git a/src/compress/flate/testdata/huffman-rand-limit.wb.expect b/src/compress/flate/testdata/huffman-rand-limit.wb.expect
new file mode 100644
index 0000000..881e59c
--- /dev/null
+++ b/src/compress/flate/testdata/huffman-rand-limit.wb.expect
diff --git a/src/compress/flate/testdata/huffman-rand-limit.wb.expect-noinput b/src/compress/flate/testdata/huffman-rand-limit.wb.expect-noinput
new file mode 100644
index 0000000..881e59c
--- /dev/null
+++ b/src/compress/flate/testdata/huffman-rand-limit.wb.expect-noinput
diff --git a/src/compress/flate/testdata/huffman-rand-max.golden b/src/compress/flate/testdata/huffman-rand-max.golden
new file mode 100644
index 0000000..47d53c8
--- /dev/null
+++ b/src/compress/flate/testdata/huffman-rand-max.golden
diff --git a/src/compress/flate/testdata/huffman-rand-max.in b/src/compress/flate/testdata/huffman-rand-max.in
new file mode 100644
index 0000000..8418633
--- /dev/null
+++ b/src/compress/flate/testdata/huffman-rand-max.in
diff --git a/src/compress/flate/testdata/huffman-shifts.dyn.expect b/src/compress/flate/testdata/huffman-shifts.dyn.expect
new file mode 100644
index 0000000..7812c1c
--- /dev/null
+++ b/src/compress/flate/testdata/huffman-shifts.dyn.expect
diff --git a/src/compress/flate/testdata/huffman-shifts.dyn.expect-noinput b/src/compress/flate/testdata/huffman-shifts.dyn.expect-noinput
new file mode 100644
index 0000000..7812c1c
--- /dev/null
+++ b/src/compress/flate/testdata/huffman-shifts.dyn.expect-noinput
diff --git a/src/compress/flate/testdata/huffman-shifts.golden b/src/compress/flate/testdata/huffman-shifts.golden
new file mode 100644
index 0000000..f513377
--- /dev/null
+++ b/src/compress/flate/testdata/huffman-shifts.golden
diff --git a/src/compress/flate/testdata/huffman-shifts.in b/src/compress/flate/testdata/huffman-shifts.in
new file mode 100644
index 0000000..7c7a50d
--- /dev/null
+++ b/src/compress/flate/testdata/huffman-shifts.in
@@ -0,0 +1,2 @@
+101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010

+232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323232323
\ No newline at end of file
diff --git a/src/compress/flate/testdata/huffman-shifts.wb.expect b/src/compress/flate/testdata/huffman-shifts.wb.expect
new file mode 100644
index 0000000..7812c1c
--- /dev/null
+++ b/src/compress/flate/testdata/huffman-shifts.wb.expect
diff --git a/src/compress/flate/testdata/huffman-shifts.wb.expect-noinput b/src/compress/flate/testdata/huffman-shifts.wb.expect-noinput
new file mode 100644
index 0000000..7812c1c
--- /dev/null
+++ b/src/compress/flate/testdata/huffman-shifts.wb.expect-noinput
diff --git a/src/compress/flate/testdata/huffman-text-shift.dyn.expect b/src/compress/flate/testdata/huffman-text-shift.dyn.expect
new file mode 100644
index 0000000..71ce3ae
--- /dev/null
+++ b/src/compress/flate/testdata/huffman-text-shift.dyn.expect
diff --git a/src/compress/flate/testdata/huffman-text-shift.dyn.expect-noinput b/src/compress/flate/testdata/huffman-text-shift.dyn.expect-noinput
new file mode 100644
index 0000000..71ce3ae
--- /dev/null
+++ b/src/compress/flate/testdata/huffman-text-shift.dyn.expect-noinput
diff --git a/src/compress/flate/testdata/huffman-text-shift.golden b/src/compress/flate/testdata/huffman-text-shift.golden
new file mode 100644
index 0000000..ff02311
--- /dev/null
+++ b/src/compress/flate/testdata/huffman-text-shift.golden
diff --git a/src/compress/flate/testdata/huffman-text-shift.in b/src/compress/flate/testdata/huffman-text-shift.in
new file mode 100644
index 0000000..cc5c3ad
--- /dev/null
+++ b/src/compress/flate/testdata/huffman-text-shift.in
@@ -0,0 +1,14 @@
+//Copyright2009ThGoAuthor.Allrightrrvd.

+//UofthiourccodigovrndbyBSD-tyl

+//licnthtcnbfoundinthLICENSEfil.

+

+pckgmin

+

+import"o"

+

+funcmin(){

+	vrb=mk([]byt,65535)

+	f,_:=o.Crt("huffmn-null-mx.in")

+	f.Writ(b)

+}

+ABCDEFGHIJKLMNOPQRSTUVXxyz!"#¤%&/?"
\ No newline at end of file
diff --git a/src/compress/flate/testdata/huffman-text-shift.wb.expect b/src/compress/flate/testdata/huffman-text-shift.wb.expect
new file mode 100644
index 0000000..71ce3ae
--- /dev/null
+++ b/src/compress/flate/testdata/huffman-text-shift.wb.expect
diff --git a/src/compress/flate/testdata/huffman-text-shift.wb.expect-noinput b/src/compress/flate/testdata/huffman-text-shift.wb.expect-noinput
new file mode 100644
index 0000000..71ce3ae
--- /dev/null
+++ b/src/compress/flate/testdata/huffman-text-shift.wb.expect-noinput
diff --git a/src/compress/flate/testdata/huffman-text.dyn.expect b/src/compress/flate/testdata/huffman-text.dyn.expect
new file mode 100644
index 0000000..d448727
--- /dev/null
+++ b/src/compress/flate/testdata/huffman-text.dyn.expect
@@ -0,0 +1 @@
+�_K�0������`K��0Aasě)^�H�����Iɟb߻��_>�4
a��=����-^
�1`_�	1	���	�ő:�Y��-�F66!�A��`�a��C;A����Nyr4ߜU�!���GKС��#�����r:B[G�3��.�L��׶�bFRuM]���^⇳�(#Z������i�����v��B����B�H2S]��u/���ֽ��W�T�G��n���r�
\ No newline at end of file
diff --git a/src/compress/flate/testdata/huffman-text.dyn.expect-noinput b/src/compress/flate/testdata/huffman-text.dyn.expect-noinput
new file mode 100644
index 0000000..d448727
--- /dev/null
+++ b/src/compress/flate/testdata/huffman-text.dyn.expect-noinput
@@ -0,0 +1 @@
+�_K�0������`K��0Aasě)^�H�����Iɟb߻��_>�4
a��=����-^
�1`_�	1	���	�ő:�Y��-�F66!�A��`�a��C;A����Nyr4ߜU�!���GKС��#�����r:B[G�3��.�L��׶�bFRuM]���^⇳�(#Z������i�����v��B����B�H2S]��u/���ֽ��W�T�G��n���r�
\ No newline at end of file
diff --git a/src/compress/flate/testdata/huffman-text.golden b/src/compress/flate/testdata/huffman-text.golden
new file mode 100644
index 0000000..6d34c61
--- /dev/null
+++ b/src/compress/flate/testdata/huffman-text.golden
@@ -0,0 +1,3 @@
+�AK�0��x�ß�Z���LP�a�!�x��AD��I�&#I�E�����p]�Lƿ���F�p��	1�88�h��$���5S��-	�F66!�)v�.��0�Y�������&��	S���N|d�2:��
+t�|둍���xz9������骺�����Ɏ�3��
+&&=������ô�UD�=Fu���]��q����UL+�����>FQY��LZ��o���fTߵ�EŴ��{�Yʶb�e�
\ No newline at end of file
diff --git a/src/compress/flate/testdata/huffman-text.in b/src/compress/flate/testdata/huffman-text.in
new file mode 100644
index 0000000..73398b9
--- /dev/null
+++ b/src/compress/flate/testdata/huffman-text.in
@@ -0,0 +1,13 @@
+// Copyright 2009 The Go Authors. All rights reserved.

+// Use of this source code is governed by a BSD-style

+// license that can be found in the LICENSE file.

+

+package main

+

+import "os"

+

+func main() {

+	var b = make([]byte, 65535)

+	f, _ := os.Create("huffman-null-max.in")

+	f.Write(b)

+}

diff --git a/src/compress/flate/testdata/huffman-text.wb.expect b/src/compress/flate/testdata/huffman-text.wb.expect
new file mode 100644
index 0000000..d448727
--- /dev/null
+++ b/src/compress/flate/testdata/huffman-text.wb.expect
@@ -0,0 +1 @@
+�_K�0������`K��0Aasě)^�H�����Iɟb߻��_>�4
a��=����-^
�1`_�	1	���	�ő:�Y��-�F66!�A��`�a��C;A����Nyr4ߜU�!���GKС��#�����r:B[G�3��.�L��׶�bFRuM]���^⇳�(#Z������i�����v��B����B�H2S]��u/���ֽ��W�T�G��n���r�
\ No newline at end of file
diff --git a/src/compress/flate/testdata/huffman-text.wb.expect-noinput b/src/compress/flate/testdata/huffman-text.wb.expect-noinput
new file mode 100644
index 0000000..d448727
--- /dev/null
+++ b/src/compress/flate/testdata/huffman-text.wb.expect-noinput
@@ -0,0 +1 @@
+�_K�0������`K��0Aasě)^�H�����Iɟb߻��_>�4
a��=����-^
�1`_�	1	���	�ő:�Y��-�F66!�A��`�a��C;A����Nyr4ߜU�!���GKС��#�����r:B[G�3��.�L��׶�bFRuM]���^⇳�(#Z������i�����v��B����B�H2S]��u/���ֽ��W�T�G��n���r�
\ No newline at end of file
diff --git a/src/compress/flate/testdata/huffman-zero.dyn.expect b/src/compress/flate/testdata/huffman-zero.dyn.expect
new file mode 100644
index 0000000..830348a
--- /dev/null
+++ b/src/compress/flate/testdata/huffman-zero.dyn.expect
diff --git a/src/compress/flate/testdata/huffman-zero.dyn.expect-noinput b/src/compress/flate/testdata/huffman-zero.dyn.expect-noinput
new file mode 100644
index 0000000..830348a
--- /dev/null
+++ b/src/compress/flate/testdata/huffman-zero.dyn.expect-noinput
diff --git a/src/compress/flate/testdata/huffman-zero.golden b/src/compress/flate/testdata/huffman-zero.golden
new file mode 100644
index 0000000..5abdbaf
--- /dev/null
+++ b/src/compress/flate/testdata/huffman-zero.golden
diff --git a/src/compress/flate/testdata/huffman-zero.in b/src/compress/flate/testdata/huffman-zero.in
new file mode 100644
index 0000000..349be0e
--- /dev/null
+++ b/src/compress/flate/testdata/huffman-zero.in
@@ -0,0 +1 @@
+00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000
\ No newline at end of file
diff --git a/src/compress/flate/testdata/huffman-zero.wb.expect b/src/compress/flate/testdata/huffman-zero.wb.expect
new file mode 100644
index 0000000..dbe401c
--- /dev/null
+++ b/src/compress/flate/testdata/huffman-zero.wb.expect
diff --git a/src/compress/flate/testdata/huffman-zero.wb.expect-noinput b/src/compress/flate/testdata/huffman-zero.wb.expect-noinput
new file mode 100644
index 0000000..dbe401c
--- /dev/null
+++ b/src/compress/flate/testdata/huffman-zero.wb.expect-noinput
diff --git a/src/compress/flate/testdata/null-long-match.dyn.expect-noinput b/src/compress/flate/testdata/null-long-match.dyn.expect-noinput
new file mode 100644
index 0000000..8b92d9f
--- /dev/null
+++ b/src/compress/flate/testdata/null-long-match.dyn.expect-noinput
diff --git a/src/compress/flate/testdata/null-long-match.wb.expect-noinput b/src/compress/flate/testdata/null-long-match.wb.expect-noinput
new file mode 100644
index 0000000..8b92d9f
--- /dev/null
+++ b/src/compress/flate/testdata/null-long-match.wb.expect-noinput
diff --git a/src/compress/flate/token.go b/src/compress/flate/token.go
new file mode 100644
index 0000000..ae01391
--- /dev/null
+++ b/src/compress/flate/token.go
@@ -0,0 +1,97 @@
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package flate
+
+const (
+	// 2 bits:   type   0 = literal  1=EOF  2=Match   3=Unused
+	// 8 bits:   xlength = length - MIN_MATCH_LENGTH
+	// 22 bits   xoffset = offset - MIN_OFFSET_SIZE, or literal
+	lengthShift = 22
+	offsetMask  = 1<<lengthShift - 1
+	typeMask    = 3 << 30
+	literalType = 0 << 30
+	matchType   = 1 << 30
+)
+
+// The length code for length X (MIN_MATCH_LENGTH <= X <= MAX_MATCH_LENGTH)
+// is lengthCodes[length - MIN_MATCH_LENGTH]
+var lengthCodes = [...]uint32{
+	0, 1, 2, 3, 4, 5, 6, 7, 8, 8,
+	9, 9, 10, 10, 11, 11, 12, 12, 12, 12,
+	13, 13, 13, 13, 14, 14, 14, 14, 15, 15,
+	15, 15, 16, 16, 16, 16, 16, 16, 16, 16,
+	17, 17, 17, 17, 17, 17, 17, 17, 18, 18,
+	18, 18, 18, 18, 18, 18, 19, 19, 19, 19,
+	19, 19, 19, 19, 20, 20, 20, 20, 20, 20,
+	20, 20, 20, 20, 20, 20, 20, 20, 20, 20,
+	21, 21, 21, 21, 21, 21, 21, 21, 21, 21,
+	21, 21, 21, 21, 21, 21, 22, 22, 22, 22,
+	22, 22, 22, 22, 22, 22, 22, 22, 22, 22,
+	22, 22, 23, 23, 23, 23, 23, 23, 23, 23,
+	23, 23, 23, 23, 23, 23, 23, 23, 24, 24,
+	24, 24, 24, 24, 24, 24, 24, 24, 24, 24,
+	24, 24, 24, 24, 24, 24, 24, 24, 24, 24,
+	24, 24, 24, 24, 24, 24, 24, 24, 24, 24,
+	25, 25, 25, 25, 25, 25, 25, 25, 25, 25,
+	25, 25, 25, 25, 25, 25, 25, 25, 25, 25,
+	25, 25, 25, 25, 25, 25, 25, 25, 25, 25,
+	25, 25, 26, 26, 26, 26, 26, 26, 26, 26,
+	26, 26, 26, 26, 26, 26, 26, 26, 26, 26,
+	26, 26, 26, 26, 26, 26, 26, 26, 26, 26,
+	26, 26, 26, 26, 27, 27, 27, 27, 27, 27,
+	27, 27, 27, 27, 27, 27, 27, 27, 27, 27,
+	27, 27, 27, 27, 27, 27, 27, 27, 27, 27,
+	27, 27, 27, 27, 27, 28,
+}
+
+var offsetCodes = [...]uint32{
+	0, 1, 2, 3, 4, 4, 5, 5, 6, 6, 6, 6, 7, 7, 7, 7,
+	8, 8, 8, 8, 8, 8, 8, 8, 9, 9, 9, 9, 9, 9, 9, 9,
+	10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10,
+	11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11,
+	12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12,
+	12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12,
+	13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13,
+	13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13,
+	14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14,
+	14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14,
+	14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14,
+	14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14,
+	15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15,
+	15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15,
+	15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15,
+	15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15,
+}
+
+type token uint32
+
+// Convert a literal into a literal token.
+func literalToken(literal uint32) token { return token(literalType + literal) }
+
+// Convert a < xlength, xoffset > pair into a match token.
+func matchToken(xlength uint32, xoffset uint32) token {
+	return token(matchType + xlength<<lengthShift + xoffset)
+}
+
+// Returns the literal of a literal token
+func (t token) literal() uint32 { return uint32(t - literalType) }
+
+// Returns the extra offset of a match token
+func (t token) offset() uint32 { return uint32(t) & offsetMask }
+
+func (t token) length() uint32 { return uint32((t - matchType) >> lengthShift) }
+
+func lengthCode(len uint32) uint32 { return lengthCodes[len] }
+
+// Returns the offset code corresponding to a specific offset
+func offsetCode(off uint32) uint32 {
+	if off < uint32(len(offsetCodes)) {
+		return offsetCodes[off]
+	}
+	if off>>7 < uint32(len(offsetCodes)) {
+		return offsetCodes[off>>7] + 14
+	}
+	return offsetCodes[off>>14] + 28
+}
diff --git a/src/compress/flate/writer_test.go b/src/compress/flate/writer_test.go
new file mode 100644
index 0000000..c413735
--- /dev/null
+++ b/src/compress/flate/writer_test.go
@@ -0,0 +1,237 @@
+// Copyright 2012 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package flate
+
+import (
+	"bytes"
+	"fmt"
+	"io"
+	"math/rand"
+	"runtime"
+	"testing"
+)
+
+func BenchmarkEncode(b *testing.B) {
+	doBench(b, func(b *testing.B, buf0 []byte, level, n int) {
+		b.StopTimer()
+		b.SetBytes(int64(n))
+
+		buf1 := make([]byte, n)
+		for i := 0; i < n; i += len(buf0) {
+			if len(buf0) > n-i {
+				buf0 = buf0[:n-i]
+			}
+			copy(buf1[i:], buf0)
+		}
+		buf0 = nil
+		w, err := NewWriter(io.Discard, level)
+		if err != nil {
+			b.Fatal(err)
+		}
+		runtime.GC()
+		b.StartTimer()
+		for i := 0; i < b.N; i++ {
+			w.Reset(io.Discard)
+			w.Write(buf1)
+			w.Close()
+		}
+	})
+}
+
+// errorWriter is a writer that fails after N writes.
+type errorWriter struct {
+	N int
+}
+
+func (e *errorWriter) Write(b []byte) (int, error) {
+	if e.N <= 0 {
+		return 0, io.ErrClosedPipe
+	}
+	e.N--
+	return len(b), nil
+}
+
+// Test if errors from the underlying writer is passed upwards.
+func TestWriteError(t *testing.T) {
+	t.Parallel()
+	buf := new(bytes.Buffer)
+	n := 65536
+	if !testing.Short() {
+		n *= 4
+	}
+	for i := 0; i < n; i++ {
+		fmt.Fprintf(buf, "asdasfasf%d%dfghfgujyut%dyutyu\n", i, i, i)
+	}
+	in := buf.Bytes()
+	// We create our own buffer to control number of writes.
+	copyBuffer := make([]byte, 128)
+	for l := 0; l < 10; l++ {
+		for fail := 1; fail <= 256; fail *= 2 {
+			// Fail after 'fail' writes
+			ew := &errorWriter{N: fail}
+			w, err := NewWriter(ew, l)
+			if err != nil {
+				t.Fatalf("NewWriter: level %d: %v", l, err)
+			}
+			n, err := io.CopyBuffer(w, struct{ io.Reader }{bytes.NewBuffer(in)}, copyBuffer)
+			if err == nil {
+				t.Fatalf("Level %d: Expected an error, writer was %#v", l, ew)
+			}
+			n2, err := w.Write([]byte{1, 2, 2, 3, 4, 5})
+			if n2 != 0 {
+				t.Fatal("Level", l, "Expected 0 length write, got", n)
+			}
+			if err == nil {
+				t.Fatal("Level", l, "Expected an error")
+			}
+			err = w.Flush()
+			if err == nil {
+				t.Fatal("Level", l, "Expected an error on flush")
+			}
+			err = w.Close()
+			if err == nil {
+				t.Fatal("Level", l, "Expected an error on close")
+			}
+
+			w.Reset(io.Discard)
+			n2, err = w.Write([]byte{1, 2, 3, 4, 5, 6})
+			if err != nil {
+				t.Fatal("Level", l, "Got unexpected error after reset:", err)
+			}
+			if n2 == 0 {
+				t.Fatal("Level", l, "Got 0 length write, expected > 0")
+			}
+			if testing.Short() {
+				return
+			}
+		}
+	}
+}
+
+// Test if two runs produce identical results
+// even when writing different sizes to the Writer.
+func TestDeterministic(t *testing.T) {
+	t.Parallel()
+	for i := 0; i <= 9; i++ {
+		t.Run(fmt.Sprint("L", i), func(t *testing.T) { testDeterministic(i, t) })
+	}
+	t.Run("LM2", func(t *testing.T) { testDeterministic(-2, t) })
+}
+
+func testDeterministic(i int, t *testing.T) {
+	t.Parallel()
+	// Test so much we cross a good number of block boundaries.
+	var length = maxStoreBlockSize*30 + 500
+	if testing.Short() {
+		length /= 10
+	}
+
+	// Create a random, but compressible stream.
+	rng := rand.New(rand.NewSource(1))
+	t1 := make([]byte, length)
+	for i := range t1 {
+		t1[i] = byte(rng.Int63() & 7)
+	}
+
+	// Do our first encode.
+	var b1 bytes.Buffer
+	br := bytes.NewBuffer(t1)
+	w, err := NewWriter(&b1, i)
+	if err != nil {
+		t.Fatal(err)
+	}
+	// Use a very small prime sized buffer.
+	cbuf := make([]byte, 787)
+	_, err = io.CopyBuffer(w, struct{ io.Reader }{br}, cbuf)
+	if err != nil {
+		t.Fatal(err)
+	}
+	w.Close()
+
+	// We choose a different buffer size,
+	// bigger than a maximum block, and also a prime.
+	var b2 bytes.Buffer
+	cbuf = make([]byte, 81761)
+	br2 := bytes.NewBuffer(t1)
+	w2, err := NewWriter(&b2, i)
+	if err != nil {
+		t.Fatal(err)
+	}
+	_, err = io.CopyBuffer(w2, struct{ io.Reader }{br2}, cbuf)
+	if err != nil {
+		t.Fatal(err)
+	}
+	w2.Close()
+
+	b1b := b1.Bytes()
+	b2b := b2.Bytes()
+
+	if !bytes.Equal(b1b, b2b) {
+		t.Errorf("level %d did not produce deterministic result, result mismatch, len(a) = %d, len(b) = %d", i, len(b1b), len(b2b))
+	}
+}
+
+// TestDeflateFast_Reset will test that encoding is consistent
+// across a warparound of the table offset.
+// See https://github.com/golang/go/issues/34121
+func TestDeflateFast_Reset(t *testing.T) {
+	buf := new(bytes.Buffer)
+	n := 65536
+
+	for i := 0; i < n; i++ {
+		fmt.Fprintf(buf, "asdfasdfasdfasdf%d%dfghfgujyut%dyutyu\n", i, i, i)
+	}
+	// This is specific to level 1.
+	const level = 1
+	in := buf.Bytes()
+	offset := 1
+	if testing.Short() {
+		offset = 256
+	}
+
+	// We do an encode with a clean buffer to compare.
+	var want bytes.Buffer
+	w, err := NewWriter(&want, level)
+	if err != nil {
+		t.Fatalf("NewWriter: level %d: %v", level, err)
+	}
+
+	// Output written 3 times.
+	w.Write(in)
+	w.Write(in)
+	w.Write(in)
+	w.Close()
+
+	for ; offset <= 256; offset *= 2 {
+		w, err := NewWriter(io.Discard, level)
+		if err != nil {
+			t.Fatalf("NewWriter: level %d: %v", level, err)
+		}
+
+		// Reset until we are right before the wraparound.
+		// Each reset adds maxMatchOffset to the offset.
+		for i := 0; i < (bufferReset-len(in)-offset-maxMatchOffset)/maxMatchOffset; i++ {
+			// skip ahead to where we are close to wrap around...
+			w.d.reset(nil)
+		}
+		var got bytes.Buffer
+		w.Reset(&got)
+
+		// Write 3 times, close.
+		for i := 0; i < 3; i++ {
+			_, err = w.Write(in)
+			if err != nil {
+				t.Fatal(err)
+			}
+		}
+		err = w.Close()
+		if err != nil {
+			t.Fatal(err)
+		}
+		if !bytes.Equal(got.Bytes(), want.Bytes()) {
+			t.Fatalf("output did not match at wraparound, len(want)  = %d, len(got) = %d", want.Len(), got.Len())
+		}
+	}
+}