61 lines
1.1 KiB
C
61 lines
1.1 KiB
C
/*
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* Copyright 2013 Haiku, Inc. All rights reserved.
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* Distributed under the terms of the MIT License.
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*
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* Authors:
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* Paweł Dziepak, pdziepak@quarnos.org
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*/
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#ifndef KERNEL_UTIL_BITUTIL_H
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#define KERNEL_UTIL_BITUTIL_H
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#include <SupportDefs.h>
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// http://graphics.stanford.edu/~seander/bithacks.html
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static inline uint32
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next_power_of_2(uint32 v)
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{
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v--;
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v |= v >> 1;
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v |= v >> 2;
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v |= v >> 4;
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v |= v >> 8;
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v |= v >> 16;
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v++;
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return v;
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}
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// http://graphics.stanford.edu/~seander/bithacks.html
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static inline uint32
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count_set_bits(uint32 v)
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{
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v = v - ((v >> 1) & 0x55555555);
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v = (v & 0x33333333) + ((v >> 2) & 0x33333333);
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return (((v + (v >> 4)) & 0xF0F0F0F) * 0x1010101) >> 24;
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}
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static inline uint32
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log2(uint32 v)
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{
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static const int MultiplyDeBruijnBitPosition[32] = {
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0, 9, 1, 10, 13, 21, 2, 29, 11, 14, 16, 18, 22, 25, 3, 30,
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8, 12, 20, 28, 15, 17, 24, 7, 19, 27, 23, 6, 26, 5, 4, 31
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};
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v |= v >> 1;
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v |= v >> 2;
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v |= v >> 4;
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v |= v >> 8;
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v |= v >> 16;
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return MultiplyDeBruijnBitPosition[(uint32)(v * 0x07C4ACDDU) >> 27];
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}
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#endif // KERNEL_UTIL_RANDOM_H
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