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Micro-optimize pop_1st_bit() for 32 bits

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Small perft speed-up of 2% and also a code
simplification.

No functional change.

Signed-off-by: Marco Costalba <mcostalba@gmail.com>
This commit is contained in:
Marco Costalba 2012-02-13 09:52:58 +01:00
parent 7b4b65d7a9
commit 3b906ffc27
1 changed files with 10 additions and 16 deletions
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26
src/bitboard.cpp
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@ -112,7 +112,7 @@ Square first_1(Bitboard b) {
// Use type-punning // Use type-punning
union b_union { union b_union {
Bitboard b; Bitboard dummy;
struct { struct {
#if defined (BIGENDIAN) #if defined (BIGENDIAN)
uint32_t h; uint32_t h;
@ -121,27 +121,21 @@ union b_union {
uint32_t l; uint32_t l;
uint32_t h; uint32_t h;
#endif #endif
} dw; } b;
}; };
Square pop_1st_bit(Bitboard* bb) { Square pop_1st_bit(Bitboard* b) {
b_union u; const b_union u = *((b_union*)b);
Square ret;
u.b = *bb; if (u.b.l)
if (u.dw.l)
{ {
ret = Square(BSFTable[((u.dw.l ^ (u.dw.l - 1)) * 0x783A9B23) >> 26]); ((b_union*)b)->b.l = u.b.l & (u.b.l - 1);
u.dw.l &= (u.dw.l - 1); return Square(BSFTable[((u.b.l ^ (u.b.l - 1)) * 0x783A9B23) >> 26]);
*bb = u.b;
return ret;
} }
ret = Square(BSFTable[((~(u.dw.h ^ (u.dw.h - 1))) * 0x783A9B23) >> 26]);
u.dw.h &= (u.dw.h - 1); ((b_union*)b)->b.h = u.b.h & (u.b.h - 1);
*bb = u.b; return Square(BSFTable[((~(u.b.h ^ (u.b.h - 1))) * 0x783A9B23) >> 26]);
return ret;
} }
#endif // !defined(USE_BSFQ) #endif // !defined(USE_BSFQ)