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// 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.
// MD4 block step.
// In its own file so that a faster assembly or C version
// can be substituted easily.
package md4
var shift1 = []uint{3, 7, 11, 19}
var shift2 = []uint{3, 5, 9, 13}
var shift3 = []uint{3, 9, 11, 15}
var xIndex2 = []uint{0, 4, 8, 12, 1, 5, 9, 13, 2, 6, 10, 14, 3, 7, 11, 15}
var xIndex3 = []uint{0, 8, 4, 12, 2, 10, 6, 14, 1, 9, 5, 13, 3, 11, 7, 15}
func _Block(dig *digest, p []byte) int {
a := dig.s[0]
b := dig.s[1]
c := dig.s[2]
d := dig.s[3]
n := 0
var X [16]uint32
for len(p) >= _Chunk {
aa, bb, cc, dd := a, b, c, d
j := 0
for i := 0; i < 16; i++ {
X[i] = uint32(p[j]) | uint32(p[j+1])<<8 | uint32(p[j+2])<<16 | uint32(p[j+3])<<24
j += 4
}
// If this needs to be made faster in the future,
// the usual trick is to unroll each of these
// loops by a factor of 4; that lets you replace
// the shift[] lookups with constants and,
// with suitable variable renaming in each
// unrolled body, delete the a, b, c, d = d, a, b, c
// (or you can let the optimizer do the renaming).
//
// The index variables are uint so that % by a power
// of two can be optimized easily by a compiler.
// Round 1.
for i := uint(0); i < 16; i++ {
x := i
s := shift1[i%4]
f := ((c ^ d) & b) ^ d
a += f + X[x]
a = a<<s | a>>(32-s)
a, b, c, d = d, a, b, c
}
// Round 2.
for i := uint(0); i < 16; i++ {
x := xIndex2[i]
s := shift2[i%4]
g := (b & c) | (b & d) | (c & d)
a += g + X[x] + 0x5a827999
a = a<<s | a>>(32-s)
a, b, c, d = d, a, b, c
}
// Round 3.
for i := uint(0); i < 16; i++ {
x := xIndex3[i]
s := shift3[i%4]
h := b ^ c ^ d
a += h + X[x] + 0x6ed9eba1
a = a<<s | a>>(32-s)
a, b, c, d = d, a, b, c
}
a += aa
b += bb
c += cc
d += dd
p = p[_Chunk:]
n += _Chunk
}
dig.s[0] = a
dig.s[1] = b
dig.s[2] = c
dig.s[3] = d
return n
}
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