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Code Issues Releases Wiki Activity

Use new 64 bit De Bruijn BitScan

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Allows to sync 32 and 64 bits implementations.

Idea by Kim Walisch, reported by Gerd Isenberg:
http://talkchess.com/forum/viewtopic.php?t=45554

No functional change.
This commit is contained in:
Marco Costalba 2012-10-13 13:34:50 +02:00
parent 189b6fc270
commit c2cd75843e
1 changed files with 4 additions and 6 deletions
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10
src/bitboard.cpp
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@ -57,7 +57,7 @@ int SquareDistance[64][64];
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
@ -75,12 +75,10 @@ namespace {
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;
}
}