mirror of
https://github.com/official-stockfish/Stockfish.git
synced 2026-07-23 13:17:12 +00:00
Marco Costalba
6b5322ce00
It seems more accurate: lsb is clear while 'first bit' depends from where you look at the bitboard. And fix compile in case of 64 bits platforms that do not use BSFQ intrinsics. No functional change. Signed-off-by: Marco Costalba <mcostalba@gmail.com>
113 lines
3.2 KiB
C++
113 lines
3.2 KiB
C++
/*
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Stockfish, a UCI chess playing engine derived from Glaurung 2.1
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Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
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Copyright (C) 2008-2012 Marco Costalba, Joona Kiiski, Tord Romstad
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Stockfish is free software: you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation, either version 3 of the License, or
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(at your option) any later version.
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Stockfish is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with this program. If not, see <http://www.gnu.org/licenses/>.
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*/
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#if !defined(BITCOUNT_H_INCLUDED)
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#define BITCOUNT_H_INCLUDED
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#include <cassert>
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#include "types.h"
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enum BitCountType {
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CNT_64,
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CNT_64_MAX15,
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CNT_32,
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CNT_32_MAX15,
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CNT_HW_POPCNT
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};
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/// Determine at compile time the best popcount<> specialization according if
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/// platform is 32 or 64 bits, to the maximum number of nonzero bits to count or
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/// use hardware popcnt instruction when available.
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const BitCountType Full = HasPopCnt ? CNT_HW_POPCNT : Is64Bit ? CNT_64 : CNT_32;
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const BitCountType Max15 = HasPopCnt ? CNT_HW_POPCNT : Is64Bit ? CNT_64_MAX15 : CNT_32_MAX15;
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/// popcount() counts the number of nonzero bits in a bitboard
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template<BitCountType> inline int popcount(Bitboard);
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template<>
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inline int popcount<CNT_64>(Bitboard b) {
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b -= ((b>>1) & 0x5555555555555555ULL);
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b = ((b>>2) & 0x3333333333333333ULL) + (b & 0x3333333333333333ULL);
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b = ((b>>4) + b) & 0x0F0F0F0F0F0F0F0FULL;
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b *= 0x0101010101010101ULL;
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return int(b >> 56);
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}
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template<>
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inline int popcount<CNT_64_MAX15>(Bitboard b) {
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b -= (b>>1) & 0x5555555555555555ULL;
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b = ((b>>2) & 0x3333333333333333ULL) + (b & 0x3333333333333333ULL);
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b *= 0x1111111111111111ULL;
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return int(b >> 60);
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}
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template<>
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inline int popcount<CNT_32>(Bitboard b) {
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unsigned w = unsigned(b >> 32), v = unsigned(b);
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v -= (v >> 1) & 0x55555555; // 0-2 in 2 bits
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w -= (w >> 1) & 0x55555555;
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v = ((v >> 2) & 0x33333333) + (v & 0x33333333); // 0-4 in 4 bits
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w = ((w >> 2) & 0x33333333) + (w & 0x33333333);
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v = ((v >> 4) + v) & 0x0F0F0F0F; // 0-8 in 8 bits
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v += (((w >> 4) + w) & 0x0F0F0F0F); // 0-16 in 8 bits
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v *= 0x01010101; // mul is fast on amd procs
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return int(v >> 24);
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}
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template<>
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inline int popcount<CNT_32_MAX15>(Bitboard b) {
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unsigned w = unsigned(b >> 32), v = unsigned(b);
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v -= (v >> 1) & 0x55555555; // 0-2 in 2 bits
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w -= (w >> 1) & 0x55555555;
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v = ((v >> 2) & 0x33333333) + (v & 0x33333333); // 0-4 in 4 bits
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w = ((w >> 2) & 0x33333333) + (w & 0x33333333);
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v += w; // 0-8 in 4 bits
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v *= 0x11111111;
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return int(v >> 28);
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}
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template<>
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inline int popcount<CNT_HW_POPCNT>(Bitboard b) {
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#if !defined(USE_POPCNT)
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assert(false);
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return b != 0; // Avoid 'b not used' warning
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#elif defined(_MSC_VER) && defined(__INTEL_COMPILER)
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return _mm_popcnt_u64(b);
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#elif defined(_MSC_VER)
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return (int)__popcnt64(b);
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#else
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unsigned long ret;
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__asm__("popcnt %1, %0" : "=r" (ret) : "r" (b));
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return ret;
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#endif
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}
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#endif // !defined(BITCOUNT_H_INCLUDED)
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