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48 lines
1.1 KiB
48 lines
1.1 KiB
// Copyright 2014-2021 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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/*
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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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*/
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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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