diff options
Diffstat (limited to 'libgo/go/hash/adler32')
| -rw-r--r-- | libgo/go/hash/adler32/adler32.go | 88 | ||||
| -rw-r--r-- | libgo/go/hash/adler32/adler32_test.go | 63 |
2 files changed, 151 insertions, 0 deletions
diff --git a/libgo/go/hash/adler32/adler32.go b/libgo/go/hash/adler32/adler32.go new file mode 100644 index 000000000..cd0c2599a --- /dev/null +++ b/libgo/go/hash/adler32/adler32.go @@ -0,0 +1,88 @@ +// 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 package implements the Adler-32 checksum. +// 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 ( + "hash" + "os" +) + +const ( + mod = 65521 +) + +// The size of an Adler-32 checksum in bytes. +const Size = 4 + +// digest represents the partial evaluation of a checksum. +type digest struct { + // invariant: (a < mod && b < mod) || a <= b + // invariant: a + b + 255 <= 0xffffffff + a, b uint32 +} + +func (d *digest) Reset() { d.a, d.b = 1, 0 } + +// New returns a new hash.Hash32 computing the Adler-32 checksum. +func New() hash.Hash32 { + d := new(digest) + d.Reset() + return d +} + +func (d *digest) Size() int { return Size } + +// Add p to the running checksum a, b. +func update(a, b uint32, p []byte) (aa, bb uint32) { + for i := 0; i < len(p); i++ { + a += uint32(p[i]) + b += a + // invariant: a <= b + if b > (0xffffffff-255)/2 { + a %= mod + b %= mod + // invariant: a < mod && b < mod + } else { + // invariant: a + b + 255 <= 2 * b + 255 <= 0xffffffff + } + } + return a, b +} + +// Return the 32-bit checksum corresponding to a, b. +func finish(a, b uint32) uint32 { + if b >= mod { + a %= mod + b %= mod + } + return b<<16 | a +} + +func (d *digest) Write(p []byte) (nn int, err os.Error) { + d.a, d.b = update(d.a, d.b, p) + return len(p), nil +} + +func (d *digest) Sum32() uint32 { return finish(d.a, d.b) } + +func (d *digest) Sum() []byte { + p := make([]byte, 4) + s := d.Sum32() + p[0] = byte(s >> 24) + p[1] = byte(s >> 16) + p[2] = byte(s >> 8) + p[3] = byte(s) + return p +} + +// Checksum returns the Adler-32 checksum of data. +func Checksum(data []byte) uint32 { return finish(update(1, 0, data)) } diff --git a/libgo/go/hash/adler32/adler32_test.go b/libgo/go/hash/adler32/adler32_test.go new file mode 100644 index 000000000..ffa5569bc --- /dev/null +++ b/libgo/go/hash/adler32/adler32_test.go @@ -0,0 +1,63 @@ +// 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 ( + "io" + "testing" +) + +type _Adler32Test struct { + out uint32 + in string +} + +var golden = []_Adler32Test{ + {0x1, ""}, + {0x620062, "a"}, + {0x12600c4, "ab"}, + {0x24d0127, "abc"}, + {0x3d8018b, "abcd"}, + {0x5c801f0, "abcde"}, + {0x81e0256, "abcdef"}, + {0xadb02bd, "abcdefg"}, + {0xe000325, "abcdefgh"}, + {0x118e038e, "abcdefghi"}, + {0x158603f8, "abcdefghij"}, + {0x3f090f02, "Discard medicine more than two years old."}, + {0x46d81477, "He who has a shady past knows that nice guys finish last."}, + {0x40ee0ee1, "I wouldn't marry him with a ten foot pole."}, + {0x16661315, "Free! Free!/A trip/to Mars/for 900/empty jars/Burma Shave"}, + {0x5b2e1480, "The days of the digital watch are numbered. -Tom Stoppard"}, + {0x8c3c09ea, "Nepal premier won't resign."}, + {0x45ac18fd, "For every action there is an equal and opposite government program."}, + {0x53c61462, "His money is twice tainted: 'taint yours and 'taint mine."}, + {0x7e511e63, "There is no reason for any individual to have a computer in their home. -Ken Olsen, 1977"}, + {0xe4801a6a, "It's a tiny change to the code and not completely disgusting. - Bob Manchek"}, + {0x61b507df, "size: a.out: bad magic"}, + {0xb8631171, "The major problem is with sendmail. -Mark Horton"}, + {0x8b5e1904, "Give me a rock, paper and scissors and I will move the world. CCFestoon"}, + {0x7cc6102b, "If the enemy is within range, then so are you."}, + {0x700318e7, "It's well we cannot hear the screams/That we create in others' dreams."}, + {0x1e601747, "You remind me of a TV show, but that's all right: I watch it anyway."}, + {0xb55b0b09, "C is as portable as Stonehedge!!"}, + {0x39111dd0, "Even if I could be Shakespeare, I think I should still choose to be Faraday. - A. Huxley"}, + {0x91dd304f, "The fugacity of a constituent in a mixture of gases at a given temperature is proportional to its mole fraction. Lewis-Randall Rule"}, + {0x2e5d1316, "How can you write a big system without C++? -Paul Glick"}, + {0xd0201df6, "'Invariant assertions' is the most elegant programming technique! -Tom Szymanski"}, +} + +func TestGolden(t *testing.T) { + for i := 0; i < len(golden); i++ { + g := golden[i] + c := New() + io.WriteString(c, g.in) + s := c.Sum32() + if s != g.out { + t.Errorf("adler32(%s) = 0x%x want 0x%x", g.in, s, g.out) + t.FailNow() + } + } +} |