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33 lines
632 B
C++
33 lines
632 B
C++
#pragma once
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#include <cstddef>
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/** Returns log2 of number, rounded down.
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* Compiles to single 'bsr' instruction on x86.
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* For zero argument, result is unspecified.
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*/
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inline unsigned int bitScanReverse(unsigned int x)
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{
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return sizeof(unsigned int) * 8 - 1 - __builtin_clz(x);
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}
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/** For zero argument, result is zero.
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* For arguments with most significand bit set, result is zero.
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* For other arguments, returns value, rounded up to power of two.
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*/
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inline size_t roundUpToPowerOfTwoOrZero(size_t n)
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{
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--n;
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n |= n >> 1;
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n |= n >> 2;
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n |= n >> 4;
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n |= n >> 8;
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n |= n >> 16;
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n |= n >> 32;
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++n;
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return n;
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}
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