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perf(core/bit_utils.h): optimize MostSignificantBit default impl #1064

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Merged
ondys merged 4 commits into from
Sep 4, 2025
Merged

perf(core/bit_utils.h): optimize MostSignificantBit default impl #1064

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perf(core/bit_utils.h): optimize MostSignificantBit default impl
servusdei2018 May 10, 2024
6d4b78c
Merge branch 'main' into main
servusdei2018 Nov 13, 2024
2280215
Merge branch 'main' into main
servusdei2018 Sep 4, 2025
45534d9
Merge branch 'main' into main
ondys Sep 4, 2025
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15 changes: 9 additions & 6 deletions src/draco/core/bit_utils.h
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Original file line number Diff line number Diff line change
Expand Up @@ -59,16 +59,19 @@ inline int MostSignificantBit(uint32_t n) {
#if defined(__GNUC__)
return 31 ^ __builtin_clz(n);
#elif defined(_MSC_VER)

unsigned long where;
_BitScanReverse(&where, n);
return (int)where;
#else
// TODO(fgalligan): Optimize this code.
int msb = -1;
while (n != 0) {
msb++;
n >>= 1;
uint32_t msb = 0;
if (n) {
if (0xFFFF0000 & n) { n >>= (1 << 4); msb |= (1 << 4); }
if (0x0000FF00 & n) { n >>= (1 << 3); msb |= (1 << 3); }
if (0x000000F0 & n) { n >>= (1 << 2); msb |= (1 << 2); }
if (0x0000000C & n) { n >>= (1 << 1); msb |= (1 << 1); }
if (0x00000002 & n) { msb |= (1 << 0); }
} else {
msb = -1;
}
return msb;
#endif
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