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42 lines
1.1 KiB
C++
42 lines
1.1 KiB
C++
// This file is under the public domain.
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#pragma once
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#include <cstddef>
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#include "CommonTypes.h"
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// Helper functions:
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#ifdef _WIN32
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#include <intrin.h>
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template <typename T>
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inline int CountSetBits(T v) {
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// from https://graphics.stanford.edu/~seander/bithacks.html
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// GCC has this built in, but MSVC's intrinsic will only emit the actual
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// POPCNT instruction, which we're not depending on
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v = v - ((v >> 1) & (T)~(T)0/3);
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v = (v & (T)~(T)0/15*3) + ((v >> 2) & (T)~(T)0/15*3);
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v = (v + (v >> 4)) & (T)~(T)0/255*15;
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return (T)(v * ((T)~(T)0/255)) >> (sizeof(T) - 1) * 8;
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}
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inline int LeastSignificantSetBit(u32 val)
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{
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unsigned long index;
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_BitScanForward(&index, val);
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return (int)index;
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}
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#ifdef _M_X64
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inline int LeastSignificantSetBit(u64 val)
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{
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unsigned long index;
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_BitScanForward64(&index, val);
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return (int)index;
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}
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#endif
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#else
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inline int CountSetBits(u32 val) { return __builtin_popcount(val); }
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inline int CountSetBits(u64 val) { return __builtin_popcountll(val); }
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inline int LeastSignificantSetBit(u32 val) { return __builtin_ctz(val); }
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inline int LeastSignificantSetBit(u64 val) { return __builtin_ctzll(val); }
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#endif
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