2 files changed, 275 insertions, 0 deletions
diff --git a/src/hash/adler32/adler32.go b/src/hash/adler32/adler32.go
new file mode 100644
index 0000000..38d644d
--- /dev/null
+++ b/src/hash/adler32/adler32.go
@@ -0,0 +1,135 @@
+// 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 adler32 implements the Adler-32 checksum.
+//
+// It is defined in RFC 1950:
+//
+//	Adler-32 is composed of two sums accumulated per byte: s1 is
+//	the sum of all bytes, s2 is the sum of all s1 values. Both sums
+//	are done modulo 65521. s1 is initialized to 1, s2 to zero.  The
+//	Adler-32 checksum is stored as s2*65536 + s1 in most-
+//	significant-byte first (network) order.
+package adler32
+
+import (
+	"errors"
+	"hash"
+)
+
+const (
+	// mod is the largest prime that is less than 65536.
+	mod = 65521
+	// nmax is the largest n such that
+	// 255 * n * (n+1) / 2 + (n+1) * (mod-1) <= 2^32-1.
+	// It is mentioned in RFC 1950 (search for "5552").
+	nmax = 5552
+)
+
+// The size of an Adler-32 checksum in bytes.
+const Size = 4
+
+// digest represents the partial evaluation of a checksum.
+// The low 16 bits are s1, the high 16 bits are s2.
+type digest uint32
+
+func (d *digest) Reset() { *d = 1 }
+
+// New returns a new hash.Hash32 computing the Adler-32 checksum. Its
+// Sum method will lay the value out in big-endian byte order. The
+// returned Hash32 also implements encoding.BinaryMarshaler and
+// encoding.BinaryUnmarshaler to marshal and unmarshal the internal
+// state of the hash.
+func New() hash.Hash32 {
+	d := new(digest)
+	d.Reset()
+	return d
+}
+
+func (d *digest) Size() int { return Size }
+
+func (d *digest) BlockSize() int { return 4 }
+
+const (
+	magic         = "adl\x01"
+	marshaledSize = len(magic) + 4
+)
+
+func (d *digest) MarshalBinary() ([]byte, error) {
+	b := make([]byte, 0, marshaledSize)
+	b = append(b, magic...)
+	b = appendUint32(b, uint32(*d))
+	return b, nil
+}
+
+func (d *digest) UnmarshalBinary(b []byte) error {
+	if len(b) < len(magic) || string(b[:len(magic)]) != magic {
+		return errors.New("hash/adler32: invalid hash state identifier")
+	}
+	if len(b) != marshaledSize {
+		return errors.New("hash/adler32: invalid hash state size")
+	}
+	*d = digest(readUint32(b[len(magic):]))
+	return nil
+}
+
+func appendUint32(b []byte, x uint32) []byte {
+	a := [4]byte{
+		byte(x >> 24),
+		byte(x >> 16),
+		byte(x >> 8),
+		byte(x),
+	}
+	return append(b, a[:]...)
+}
+
+func readUint32(b []byte) uint32 {
+	_ = b[3]
+	return uint32(b[3]) | uint32(b[2])<<8 | uint32(b[1])<<16 | uint32(b[0])<<24
+}
+
+// Add p to the running checksum d.
+func update(d digest, p []byte) digest {
+	s1, s2 := uint32(d&0xffff), uint32(d>>16)
+	for len(p) > 0 {
+		var q []byte
+		if len(p) > nmax {
+			p, q = p[:nmax], p[nmax:]
+		}
+		for len(p) >= 4 {
+			s1 += uint32(p[0])
+			s2 += s1
+			s1 += uint32(p[1])
+			s2 += s1
+			s1 += uint32(p[2])
+			s2 += s1
+			s1 += uint32(p[3])
+			s2 += s1
+			p = p[4:]
+		}
+		for _, x := range p {
+			s1 += uint32(x)
+			s2 += s1
+		}
+		s1 %= mod
+		s2 %= mod
+		p = q
+	}
+	return digest(s2<<16 | s1)
+}
+
+func (d *digest) Write(p []byte) (nn int, err error) {
+	*d = update(*d, p)
+	return len(p), nil
+}
+
+func (d *digest) Sum32() uint32 { return uint32(*d) }
+
+func (d *digest) Sum(in []byte) []byte {
+	s := uint32(*d)
+	return append(in, byte(s>>24), byte(s>>16), byte(s>>8), byte(s))
+}
+
+// Checksum returns the Adler-32 checksum of data.
+func Checksum(data []byte) uint32 { return uint32(update(1, data)) }
diff --git a/src/hash/adler32/adler32_test.go b/src/hash/adler32/adler32_test.go
new file mode 100644
index 0000000..6bac802
--- /dev/null
+++ b/src/hash/adler32/adler32_test.go
@@ -0,0 +1,140 @@
+// 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 adler32
+
+import (
+	"encoding"
+	"io"
+	"strings"
+	"testing"
+)
+
+var golden = []struct {
+	out       uint32
+	in        string
+	halfState string // marshaled hash state after first half of in written, used by TestGoldenMarshal
+}{
+	{0x00000001, "", "adl\x01\x00\x00\x00\x01"},
+	{0x00620062, "a", "adl\x01\x00\x00\x00\x01"},
+	{0x012600c4, "ab", "adl\x01\x00b\x00b"},
+	{0x024d0127, "abc", "adl\x01\x00b\x00b"},
+	{0x03d8018b, "abcd", "adl\x01\x01&\x00\xc4"},
+	{0x05c801f0, "abcde", "adl\x01\x01&\x00\xc4"},
+	{0x081e0256, "abcdef", "adl\x01\x02M\x01'"},
+	{0x0adb02bd, "abcdefg", "adl\x01\x02M\x01'"},
+	{0x0e000325, "abcdefgh", "adl\x01\x03\xd8\x01\x8b"},
+	{0x118e038e, "abcdefghi", "adl\x01\x03\xd8\x01\x8b"},
+	{0x158603f8, "abcdefghij", "adl\x01\x05\xc8\x01\xf0"},
+	{0x3f090f02, "Discard medicine more than two years old.", "adl\x01NU\a\x87"},
+	{0x46d81477, "He who has a shady past knows that nice guys finish last.", "adl\x01\x89\x8e\t\xe9"},
+	{0x40ee0ee1, "I wouldn't marry him with a ten foot pole.", "adl\x01R\t\ag"},
+	{0x16661315, "Free! Free!/A trip/to Mars/for 900/empty jars/Burma Shave", "adl\x01\u007f\xbb\t\x10"},
+	{0x5b2e1480, "The days of the digital watch are numbered.  -Tom Stoppard", "adl\x01\x99:\n~"},
+	{0x8c3c09ea, "Nepal premier won't resign.", "adl\x01\"\x05\x05\x05"},
+	{0x45ac18fd, "For every action there is an equal and opposite government program.", "adl\x01\xcc\xfa\f\x00"},
+	{0x53c61462, "His money is twice tainted: 'taint yours and 'taint mine.", "adl\x01\x93\xa9\n\b"},
+	{0x7e511e63, "There is no reason for any individual to have a computer in their home. -Ken Olsen, 1977", "adl\x01e\xf5\x10\x14"},
+	{0xe4801a6a, "It's a tiny change to the code and not completely disgusting. - Bob Manchek", "adl\x01\xee\x00\f\xb2"},
+	{0x61b507df, "size:  a.out:  bad magic", "adl\x01\x1a\xfc\x04\x1d"},
+	{0xb8631171, "The major problem is with sendmail.  -Mark Horton", "adl\x01mi\b\xdc"},
+	{0x8b5e1904, "Give me a rock, paper and scissors and I will move the world.  CCFestoon", "adl\x01\xe3\n\f\x9f"},
+	{0x7cc6102b, "If the enemy is within range, then so are you.", "adl\x01_\xe0\b\x1e"},
+	{0x700318e7, "It's well we cannot hear the screams/That we create in others' dreams.", "adl\x01ۘ\f\x87"},
+	{0x1e601747, "You remind me of a TV show, but that's all right: I watch it anyway.", "adl\x01\xcc}\v\x83"},
+	{0xb55b0b09, "C is as portable as Stonehedge!!", "adl\x01,^\x05\xad"},
+	{0x39111dd0, "Even if I could be Shakespeare, I think I should still choose to be Faraday. - A. Huxley", "adl\x01M\xd1\x0e\xc8"},
+	{0x91dd304f, "The fugacity of a constituent in a mixture of gases at a given temperature is proportional to its mole fraction.  Lewis-Randall Rule", "adl\x01#\xd8\x17\xd7"},
+	{0x2e5d1316, "How can you write a big system without C++?  -Paul Glick", "adl\x01\x8fU\n\x0f"},
+	{0xd0201df6, "'Invariant assertions' is the most elegant programming technique!  -Tom Szymanski", "adl\x01/\x98\x0e\xc4"},
+	{0x211297c8, strings.Repeat("\xff", 5548) + "8", "adl\x01\x9a\xa6\xcb\xc1"},
+	{0xbaa198c8, strings.Repeat("\xff", 5549) + "9", "adl\x01gu\xcc\xc0"},
+	{0x553499be, strings.Repeat("\xff", 5550) + "0", "adl\x01gu\xcc\xc0"},
+	{0xf0c19abe, strings.Repeat("\xff", 5551) + "1", "adl\x015CͿ"},
+	{0x8d5c9bbe, strings.Repeat("\xff", 5552) + "2", "adl\x015CͿ"},
+	{0x2af69cbe, strings.Repeat("\xff", 5553) + "3", "adl\x01\x04\x10ξ"},
+	{0xc9809dbe, strings.Repeat("\xff", 5554) + "4", "adl\x01\x04\x10ξ"},
+	{0x69189ebe, strings.Repeat("\xff", 5555) + "5", "adl\x01\xd3\xcdϽ"},
+	{0x86af0001, strings.Repeat("\x00", 1e5), "adl\x01\xc3P\x00\x01"},
+	{0x79660b4d, strings.Repeat("a", 1e5), "adl\x01\x81k\x05\xa7"},
+	{0x110588ee, strings.Repeat("ABCDEFGHIJKLMNOPQRSTUVWXYZ", 1e4), "adl\x01e\xd2\xc4p"},
+}
+
+// checksum is a slow but simple implementation of the Adler-32 checksum.
+// It is a straight port of the sample code in RFC 1950 section 9.
+func checksum(p []byte) uint32 {
+	s1, s2 := uint32(1), uint32(0)
+	for _, x := range p {
+		s1 = (s1 + uint32(x)) % mod
+		s2 = (s2 + s1) % mod
+	}
+	return s2<<16 | s1
+}
+
+func TestGolden(t *testing.T) {
+	for _, g := range golden {
+		in := g.in
+		if len(in) > 220 {
+			in = in[:100] + "..." + in[len(in)-100:]
+		}
+		p := []byte(g.in)
+		if got := checksum(p); got != g.out {
+			t.Errorf("simple implementation: checksum(%q) = 0x%x want 0x%x", in, got, g.out)
+			continue
+		}
+		if got := Checksum(p); got != g.out {
+			t.Errorf("optimized implementation: Checksum(%q) = 0x%x want 0x%x", in, got, g.out)
+			continue
+		}
+	}
+}
+
+func TestGoldenMarshal(t *testing.T) {
+	for _, g := range golden {
+		h := New()
+		h2 := New()
+
+		io.WriteString(h, g.in[:len(g.in)/2])
+
+		state, err := h.(encoding.BinaryMarshaler).MarshalBinary()
+		if err != nil {
+			t.Errorf("could not marshal: %v", err)
+			continue
+		}
+
+		if string(state) != g.halfState {
+			t.Errorf("checksum(%q) state = %q, want %q", g.in, state, g.halfState)
+			continue
+		}
+
+		if err := h2.(encoding.BinaryUnmarshaler).UnmarshalBinary(state); err != nil {
+			t.Errorf("could not unmarshal: %v", err)
+			continue
+		}
+
+		io.WriteString(h, g.in[len(g.in)/2:])
+		io.WriteString(h2, g.in[len(g.in)/2:])
+
+		if h.Sum32() != h2.Sum32() {
+			t.Errorf("checksum(%q) = 0x%x != marshaled (0x%x)", g.in, h.Sum32(), h2.Sum32())
+		}
+	}
+}
+
+func BenchmarkAdler32KB(b *testing.B) {
+	b.SetBytes(1024)
+	data := make([]byte, 1024)
+	for i := range data {
+		data[i] = byte(i)
+	}
+	h := New()
+	in := make([]byte, 0, h.Size())
+
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		h.Reset()
+		h.Write(data)
+		h.Sum(in)
+	}
+}