1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
|
// 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
}
// appendUint32 is semantically the same as [binary.BigEndian.AppendUint32]
// We copied this function because we can not import "encoding/binary" here.
func appendUint32(b []byte, x uint32) []byte {
return append(b,
byte(x>>24),
byte(x>>16),
byte(x>>8),
byte(x),
)
}
// readUint32 is semantically the same as [binary.BigEndian.Uint32]
// We copied this function because we can not import "encoding/binary" here.
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)) }
|
