kate/BadFish
1
0
Fork 0
mirror of https://github.com/sockspls/badfish synced 2025-04-30 16:53:09 +00:00
Code Issues Releases Wiki Activity

Use bsfq asm instruction to count bits

Browse source 
On 64 bit systems we can use bsfq instruction to count
set bits in a bitboard.

This is a patch for GCC and Intel compilers to take advantage
of that and get a 2% speed up.

Original patch from Heinz van Saanen, adapted to current tree
by me.

No functional change.

Signed-off-by: Marco Costalba <mcostalba@gmail.com>
This commit is contained in:
Marco Costalba 2009-07-03 08:28:13 +01:00
parent 063e2441b1
commit a87ea9846d
2 changed files with 26 additions and 10 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

10
src/bitboard.cpp
View file

@ -161,7 +161,7 @@ const int RShift[64] = {
21, 22, 22, 22, 22, 22, 22, 21, 20, 21, 21, 21, 21, 21, 21, 20
};
#endif
#endif // defined(IS_64BIT)
Bitboard RMask[64];
@ -245,16 +245,16 @@ void init_bitboards() {
/// pop_1st_bit() finds and clears the least significant nonzero bit in a
/// nonzero bitboard.
#if defined(IS_64BIT)
#if defined(IS_64BIT) && !defined(USE_BSFQ)
Square pop_1st_bit(Bitboard *b) {
Square pop_1st_bit(Bitboard* b) {
Bitboard bb = *b ^ (*b - 1);
uint32_t fold = int(bb) ^ int(bb >> 32);
*b &= (*b - 1);
return Square(BitTable[(fold * 0x783a9b23) >> 26]);
}
#else
#elif !defined(USE_BSFQ)
// Use type-punning
union b_union {
@ -267,7 +267,7 @@ union b_union {
};
// WARNING: Needs -fno-strict-aliasing compiler option
Square pop_1st_bit(Bitboard *bb) {
Square pop_1st_bit(Bitboard* bb) {
b_union u;
uint32_t b;

26
src/bitboard.h
View file

@ -36,6 +36,11 @@
#define IS_64BIT
#endif
#if defined(IS_64BIT) && (defined(__GNUC__) || defined(__INTEL_COMPILER))
#define USE_BSFQ
#endif
////
//// Includes
////
@ -383,14 +388,24 @@ inline Bitboard isolated_pawn_mask(Square s) {
/// first_1() finds the least significant nonzero bit in a nonzero bitboard.
/// pop_1st_bit() finds and clears the least significant nonzero bit in a
/// nonzero bitboard.
#if defined(IS_64BIT)
#if defined(USE_BSFQ) // Assembly code by Heinz van Saanen
inline Square first_1(Bitboard b) {
return Square(BitTable[((b & -b) * 0x218a392cd3d5dbfULL) >> 58]);
inline Square __attribute__((always_inline)) first_1(Bitboard b) {
Bitboard dummy;
__asm__("bsfq %1, %0": "=r"(dummy): "rm"(b) );
return (Square)(dummy);
}
#else
inline Square __attribute__((always_inline)) pop_1st_bit(Bitboard* b) {
const Square s = first_1(*b);
*b &= ~(1ULL<<s);
return s;
}
#else // if !defined(USE_BSFQ)
inline Square first_1(Bitboard b) {
b ^= (b - 1);
@ -398,6 +413,8 @@ inline Square first_1(Bitboard b) {
return Square(BitTable[(fold * 0x783a9b23) >> 26]);
}
extern Square pop_1st_bit(Bitboard* b);
#endif
@ -407,7 +424,6 @@ inline Square first_1(Bitboard b) {
extern void print_bitboard(Bitboard b);
extern void init_bitboards();
extern Square pop_1st_bit(Bitboard *b);
#endif // !defined(BITBOARD_H_INCLUDED)