mirror of
https://github.com/vbatts/go-mtree.git
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90 lines
2 KiB
Go
90 lines
2 KiB
Go
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// Copyright 2009 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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// MD4 block step.
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// In its own file so that a faster assembly or C version
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// can be substituted easily.
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package md4
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var shift1 = []uint{3, 7, 11, 19}
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var shift2 = []uint{3, 5, 9, 13}
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var shift3 = []uint{3, 9, 11, 15}
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var xIndex2 = []uint{0, 4, 8, 12, 1, 5, 9, 13, 2, 6, 10, 14, 3, 7, 11, 15}
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var xIndex3 = []uint{0, 8, 4, 12, 2, 10, 6, 14, 1, 9, 5, 13, 3, 11, 7, 15}
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func _Block(dig *digest, p []byte) int {
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a := dig.s[0]
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b := dig.s[1]
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c := dig.s[2]
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d := dig.s[3]
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n := 0
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var X [16]uint32
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for len(p) >= _Chunk {
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aa, bb, cc, dd := a, b, c, d
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j := 0
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for i := 0; i < 16; i++ {
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X[i] = uint32(p[j]) | uint32(p[j+1])<<8 | uint32(p[j+2])<<16 | uint32(p[j+3])<<24
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j += 4
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}
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// If this needs to be made faster in the future,
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// the usual trick is to unroll each of these
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// loops by a factor of 4; that lets you replace
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// the shift[] lookups with constants and,
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// with suitable variable renaming in each
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// unrolled body, delete the a, b, c, d = d, a, b, c
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// (or you can let the optimizer do the renaming).
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//
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// The index variables are uint so that % by a power
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// of two can be optimized easily by a compiler.
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// Round 1.
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for i := uint(0); i < 16; i++ {
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x := i
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s := shift1[i%4]
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f := ((c ^ d) & b) ^ d
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a += f + X[x]
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a = a<<s | a>>(32-s)
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a, b, c, d = d, a, b, c
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}
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// Round 2.
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for i := uint(0); i < 16; i++ {
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x := xIndex2[i]
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s := shift2[i%4]
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g := (b & c) | (b & d) | (c & d)
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a += g + X[x] + 0x5a827999
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a = a<<s | a>>(32-s)
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a, b, c, d = d, a, b, c
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}
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// Round 3.
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for i := uint(0); i < 16; i++ {
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x := xIndex3[i]
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s := shift3[i%4]
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h := b ^ c ^ d
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a += h + X[x] + 0x6ed9eba1
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a = a<<s | a>>(32-s)
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a, b, c, d = d, a, b, c
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}
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a += aa
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b += bb
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c += cc
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d += dd
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p = p[_Chunk:]
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n += _Chunk
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}
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dig.s[0] = a
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dig.s[1] = b
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dig.s[2] = c
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dig.s[3] = d
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return n
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}
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