Source file src/pkg/crypto/md4/md4block.go

     1	// 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	
     9	package md4
    10	
    11	var shift1 = []uint{3, 7, 11, 19}
    12	var shift2 = []uint{3, 5, 9, 13}
    13	var shift3 = []uint{3, 9, 11, 15}
    14	
    15	var xIndex2 = []uint{0, 4, 8, 12, 1, 5, 9, 13, 2, 6, 10, 14, 3, 7, 11, 15}
    16	var xIndex3 = []uint{0, 8, 4, 12, 2, 10, 6, 14, 1, 9, 5, 13, 3, 11, 7, 15}
    17	
    18	func _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	}
The Go Programming Language

Source file src/pkg/crypto/md4/md4block.go
