1 files changed, 226 insertions, 0 deletions
diff --git a/src/hash/crc64/crc64.go b/src/hash/crc64/crc64.go
new file mode 100644
index 0000000..26b2573
--- /dev/null
+++ b/src/hash/crc64/crc64.go
@@ -0,0 +1,226 @@
+// 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 crc64 implements the 64-bit cyclic redundancy check, or CRC-64,
+// checksum. See https://en.wikipedia.org/wiki/Cyclic_redundancy_check for
+// information.
+package crc64
+
+import (
+	"errors"
+	"hash"
+	"sync"
+)
+
+// The size of a CRC-64 checksum in bytes.
+const Size = 8
+
+// Predefined polynomials.
+const (
+	// The ISO polynomial, defined in ISO 3309 and used in HDLC.
+	ISO = 0xD800000000000000
+
+	// The ECMA polynomial, defined in ECMA 182.
+	ECMA = 0xC96C5795D7870F42
+)
+
+// Table is a 256-word table representing the polynomial for efficient processing.
+type Table [256]uint64
+
+var (
+	slicing8TablesBuildOnce sync.Once
+	slicing8TableISO        *[8]Table
+	slicing8TableECMA       *[8]Table
+)
+
+func buildSlicing8TablesOnce() {
+	slicing8TablesBuildOnce.Do(buildSlicing8Tables)
+}
+
+func buildSlicing8Tables() {
+	slicing8TableISO = makeSlicingBy8Table(makeTable(ISO))
+	slicing8TableECMA = makeSlicingBy8Table(makeTable(ECMA))
+}
+
+// MakeTable returns a Table constructed from the specified polynomial.
+// The contents of this Table must not be modified.
+func MakeTable(poly uint64) *Table {
+	buildSlicing8TablesOnce()
+	switch poly {
+	case ISO:
+		return &slicing8TableISO[0]
+	case ECMA:
+		return &slicing8TableECMA[0]
+	default:
+		return makeTable(poly)
+	}
+}
+
+func makeTable(poly uint64) *Table {
+	t := new(Table)
+	for i := 0; i < 256; i++ {
+		crc := uint64(i)
+		for j := 0; j < 8; j++ {
+			if crc&1 == 1 {
+				crc = (crc >> 1) ^ poly
+			} else {
+				crc >>= 1
+			}
+		}
+		t[i] = crc
+	}
+	return t
+}
+
+func makeSlicingBy8Table(t *Table) *[8]Table {
+	var helperTable [8]Table
+	helperTable[0] = *t
+	for i := 0; i < 256; i++ {
+		crc := t[i]
+		for j := 1; j < 8; j++ {
+			crc = t[crc&0xff] ^ (crc >> 8)
+			helperTable[j][i] = crc
+		}
+	}
+	return &helperTable
+}
+
+// digest represents the partial evaluation of a checksum.
+type digest struct {
+	crc uint64
+	tab *Table
+}
+
+// New creates a new hash.Hash64 computing the CRC-64 checksum using the
+// polynomial represented by the Table. Its Sum method will lay the
+// value out in big-endian byte order. The returned Hash64 also
+// implements encoding.BinaryMarshaler and encoding.BinaryUnmarshaler to
+// marshal and unmarshal the internal state of the hash.
+func New(tab *Table) hash.Hash64 { return &digest{0, tab} }
+
+func (d *digest) Size() int { return Size }
+
+func (d *digest) BlockSize() int { return 1 }
+
+func (d *digest) Reset() { d.crc = 0 }
+
+const (
+	magic         = "crc\x02"
+	marshaledSize = len(magic) + 8 + 8
+)
+
+func (d *digest) MarshalBinary() ([]byte, error) {
+	b := make([]byte, 0, marshaledSize)
+	b = append(b, magic...)
+	b = appendUint64(b, tableSum(d.tab))
+	b = appendUint64(b, d.crc)
+	return b, nil
+}
+
+func (d *digest) UnmarshalBinary(b []byte) error {
+	if len(b) < len(magic) || string(b[:len(magic)]) != magic {
+		return errors.New("hash/crc64: invalid hash state identifier")
+	}
+	if len(b) != marshaledSize {
+		return errors.New("hash/crc64: invalid hash state size")
+	}
+	if tableSum(d.tab) != readUint64(b[4:]) {
+		return errors.New("hash/crc64: tables do not match")
+	}
+	d.crc = readUint64(b[12:])
+	return nil
+}
+
+func appendUint64(b []byte, x uint64) []byte {
+	a := [8]byte{
+		byte(x >> 56),
+		byte(x >> 48),
+		byte(x >> 40),
+		byte(x >> 32),
+		byte(x >> 24),
+		byte(x >> 16),
+		byte(x >> 8),
+		byte(x),
+	}
+	return append(b, a[:]...)
+}
+
+func readUint64(b []byte) uint64 {
+	_ = b[7]
+	return uint64(b[7]) | uint64(b[6])<<8 | uint64(b[5])<<16 | uint64(b[4])<<24 |
+		uint64(b[3])<<32 | uint64(b[2])<<40 | uint64(b[1])<<48 | uint64(b[0])<<56
+}
+
+func update(crc uint64, tab *Table, p []byte) uint64 {
+	buildSlicing8TablesOnce()
+	crc = ^crc
+	// Table comparison is somewhat expensive, so avoid it for small sizes
+	for len(p) >= 64 {
+		var helperTable *[8]Table
+		if *tab == slicing8TableECMA[0] {
+			helperTable = slicing8TableECMA
+		} else if *tab == slicing8TableISO[0] {
+			helperTable = slicing8TableISO
+			// For smaller sizes creating extended table takes too much time
+		} else if len(p) >= 2048 {
+			// According to the tests between various x86 and arm CPUs, 2k is a reasonable
+			// threshold for now. This may change in the future.
+			helperTable = makeSlicingBy8Table(tab)
+		} else {
+			break
+		}
+		// Update using slicing-by-8
+		for len(p) > 8 {
+			crc ^= uint64(p[0]) | uint64(p[1])<<8 | uint64(p[2])<<16 | uint64(p[3])<<24 |
+				uint64(p[4])<<32 | uint64(p[5])<<40 | uint64(p[6])<<48 | uint64(p[7])<<56
+			crc = helperTable[7][crc&0xff] ^
+				helperTable[6][(crc>>8)&0xff] ^
+				helperTable[5][(crc>>16)&0xff] ^
+				helperTable[4][(crc>>24)&0xff] ^
+				helperTable[3][(crc>>32)&0xff] ^
+				helperTable[2][(crc>>40)&0xff] ^
+				helperTable[1][(crc>>48)&0xff] ^
+				helperTable[0][crc>>56]
+			p = p[8:]
+		}
+	}
+	// For reminders or small sizes
+	for _, v := range p {
+		crc = tab[byte(crc)^v] ^ (crc >> 8)
+	}
+	return ^crc
+}
+
+// Update returns the result of adding the bytes in p to the crc.
+func Update(crc uint64, tab *Table, p []byte) uint64 {
+	return update(crc, tab, p)
+}
+
+func (d *digest) Write(p []byte) (n int, err error) {
+	d.crc = update(d.crc, d.tab, p)
+	return len(p), nil
+}
+
+func (d *digest) Sum64() uint64 { return d.crc }
+
+func (d *digest) Sum(in []byte) []byte {
+	s := d.Sum64()
+	return append(in, byte(s>>56), byte(s>>48), byte(s>>40), byte(s>>32), byte(s>>24), byte(s>>16), byte(s>>8), byte(s))
+}
+
+// Checksum returns the CRC-64 checksum of data
+// using the polynomial represented by the Table.
+func Checksum(data []byte, tab *Table) uint64 { return update(0, tab, data) }
+
+// tableSum returns the ISO checksum of table t.
+func tableSum(t *Table) uint64 {
+	var a [2048]byte
+	b := a[:0]
+	if t != nil {
+		for _, x := range t {
+			b = appendUint64(b, x)
+		}
+	}
+	return Checksum(b, MakeTable(ISO))
+}