namespace {
// De Bruijn sequences. See chessprogramming.wikispaces.com/BitScan
- const uint64_t DeBruijn_64 = 0x218A392CD3D5DBFULL;
+ const uint64_t DeBruijn_64 = 0x3F79D71B4CB0A89ULL;
const uint32_t DeBruijn_32 = 0x783A9B23;
CACHE_LINE_ALIGNMENT
FORCE_INLINE unsigned bsf_index(Bitboard b) {
- if (Is64Bit)
- return ((b & -b) * DeBruijn_64) >> 58;
-
- // Use Matt Taylor's folding trick for 32 bit systems
+ // Matt Taylor's folding for 32 bit systems, extended to 64 bits by Kim Walisch
b ^= (b - 1);
- return ((unsigned(b) ^ unsigned(b >> 32)) * DeBruijn_32) >> 26;
+ return Is64Bit ? (b * DeBruijn_64) >> 58
+ : ((unsigned(b) ^ unsigned(b >> 32)) * DeBruijn_32) >> 26;
}
}