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[util] Add bsf helper

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For when we know we aren't going to put in a mask of 0, we can use this and get better codegen.
This commit is contained in:
Joshua Ashton 2021-08-09 04:08:38 +01:00 committed by Joshie
parent b09b912797
commit 64f417d6e6
1 changed files with 19 additions and 0 deletions
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19
src/util/util_bit.h
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@ -76,6 +76,25 @@ namespace dxvk::bit {
#endif
}
inline uint32_t bsf(uint32_t n) {
#if defined(_MSC_VER) && !defined(__clang__)
DWORD index;
_BitScanForward(&index, n);
return uint32_t(index);
#elif defined(__GNUC__) || defined(__clang__)
return __builtin_ctz(n);
#else
uint32_t r = 31;
n &= -n;
r -= (n & 0x0000FFFF) ? 16 : 0;
r -= (n & 0x00FF00FF) ? 8 : 0;
r -= (n & 0x0F0F0F0F) ? 4 : 0;
r -= (n & 0x33333333) ? 2 : 0;
r -= (n & 0x55555555) ? 1 : 0;
return r;
#endif
}
inline uint32_t lzcnt(uint32_t n) {
#if (defined(_MSC_VER) && !defined(__clang__)) || defined(__LZCNT__)
return _lzcnt_u32(n);