989489096e
This commit implements a massive refactor of the repository, and moves the build system over to use Mage (magefile.org) which should allow seamless building across multiple platforms.
46 lines
1.1 KiB
Go
46 lines
1.1 KiB
Go
// Copyright 2014-2017 Ulrich Kunitz. 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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package lzma
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/* Naming conventions follows the CodeReviewComments in the Go Wiki. */
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// ntz32Const is used by the functions NTZ and NLZ.
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const ntz32Const = 0x04d7651f
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// ntz32Table is a helper table for de Bruijn algorithm by Danny Dubé.
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// See Henry S. Warren, Jr. "Hacker's Delight" section 5-1 figure 5-26.
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var ntz32Table = [32]int8{
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0, 1, 2, 24, 3, 19, 6, 25,
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22, 4, 20, 10, 16, 7, 12, 26,
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31, 23, 18, 5, 21, 9, 15, 11,
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30, 17, 8, 14, 29, 13, 28, 27,
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}
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// ntz32 computes the number of trailing zeros for an unsigned 32-bit integer.
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func ntz32(x uint32) int {
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if x == 0 {
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return 32
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}
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x = (x & -x) * ntz32Const
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return int(ntz32Table[x>>27])
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}
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// nlz32 computes the number of leading zeros for an unsigned 32-bit integer.
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func nlz32(x uint32) int {
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// Smear left most bit to the right
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x |= x >> 1
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x |= x >> 2
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x |= x >> 4
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x |= x >> 8
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x |= x >> 16
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// Use ntz mechanism to calculate nlz.
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x++
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if x == 0 {
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return 0
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}
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x *= ntz32Const
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return 32 - int(ntz32Table[x>>27])
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}
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