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Scott Baker8487c5d2019-10-18 12:49:46 -07001// Copyright 2009 The Go Authors. All rights reserved.
2// Use of this source code is governed by a BSD-style
3// license that can be found in the LICENSE file.
4
5// MD4 block step.
6// In its own file so that a faster assembly or C version
7// can be substituted easily.
8
9package md4
10
11var shift1 = []uint{3, 7, 11, 19}
12var shift2 = []uint{3, 5, 9, 13}
13var shift3 = []uint{3, 9, 11, 15}
14
15var xIndex2 = []uint{0, 4, 8, 12, 1, 5, 9, 13, 2, 6, 10, 14, 3, 7, 11, 15}
16var xIndex3 = []uint{0, 8, 4, 12, 2, 10, 6, 14, 1, 9, 5, 13, 3, 11, 7, 15}
17
18func _Block(dig *digest, p []byte) int {
19 a := dig.s[0]
20 b := dig.s[1]
21 c := dig.s[2]
22 d := dig.s[3]
23 n := 0
24 var X [16]uint32
25 for len(p) >= _Chunk {
26 aa, bb, cc, dd := a, b, c, d
27
28 j := 0
29 for i := 0; i < 16; i++ {
30 X[i] = uint32(p[j]) | uint32(p[j+1])<<8 | uint32(p[j+2])<<16 | uint32(p[j+3])<<24
31 j += 4
32 }
33
34 // If this needs to be made faster in the future,
35 // the usual trick is to unroll each of these
36 // loops by a factor of 4; that lets you replace
37 // the shift[] lookups with constants and,
38 // with suitable variable renaming in each
39 // unrolled body, delete the a, b, c, d = d, a, b, c
40 // (or you can let the optimizer do the renaming).
41 //
42 // The index variables are uint so that % by a power
43 // of two can be optimized easily by a compiler.
44
45 // Round 1.
46 for i := uint(0); i < 16; i++ {
47 x := i
48 s := shift1[i%4]
49 f := ((c ^ d) & b) ^ d
50 a += f + X[x]
51 a = a<<s | a>>(32-s)
52 a, b, c, d = d, a, b, c
53 }
54
55 // Round 2.
56 for i := uint(0); i < 16; i++ {
57 x := xIndex2[i]
58 s := shift2[i%4]
59 g := (b & c) | (b & d) | (c & d)
60 a += g + X[x] + 0x5a827999
61 a = a<<s | a>>(32-s)
62 a, b, c, d = d, a, b, c
63 }
64
65 // Round 3.
66 for i := uint(0); i < 16; i++ {
67 x := xIndex3[i]
68 s := shift3[i%4]
69 h := b ^ c ^ d
70 a += h + X[x] + 0x6ed9eba1
71 a = a<<s | a>>(32-s)
72 a, b, c, d = d, a, b, c
73 }
74
75 a += aa
76 b += bb
77 c += cc
78 d += dd
79
80 p = p[_Chunk:]
81 n += _Chunk
82 }
83
84 dig.s[0] = a
85 dig.s[1] = b
86 dig.s[2] = c
87 dig.s[3] = d
88 return n
89}