笔试题：如何求一个char中有几个1？ - Chinaunix

unsigned int hweight32(unsigned int w)
{
unsigned int res = w - ((w >> 1) & 0x55555555);
res = (res & 0x33333333) + ((res >> 2) & 0x33333333);
res = (res + (res >> 4)) & 0x0F0F0F0F;
res = res + (res >> 8);
return (res + (res >> 16)) & 0x000000FF;
}
#define BITMAP_LAST_WORD_MASK(nbits) \
( \
((nbits) % BITS_PER_LONG) ? \
(1UL<<((nbits) % BITS_PER_LONG))-1 : ~0UL \
)
int __bitmap_weight(const unsigned long *bitmap, int bits)
{
int k, w = 0, lim = bits/BITS_PER_LONG;
for (k = 0; k < lim; k++)
w += hweight32(bitmap[k]);
if (bits % BITS_PER_LONG)
w += hweight32(bitmap[k] & BITMAP_LAST_WORD_MASK(bits));
return w;
}

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/*
Stockfish, a UCI chess playing engine derived from Glaurung 2.1
Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
Copyright (C) 2008-2010 Marco Costalba, Joona Kiiski, Tord Romstad
Stockfish is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.
Stockfish is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
#if !defined(BITCOUNT_H_INCLUDED)
#define BITCOUNT_H_INCLUDED
#include "types.h"
enum BitCountType {
CNT64,
CNT64_MAX15,
CNT32,
CNT32_MAX15,
CNT_POPCNT
};
/// count_1s() counts the number of nonzero bits in a bitboard.
/// We have different optimized versions according if platform
/// is 32 or 64 bits, and to the maximum number of nonzero bits.
/// We also support hardware popcnt instruction. See Readme.txt
/// on how to pgo compile with popcnt support.
template<BitCountType> inline int count_1s(Bitboard);
template<>
inline int count_1s<CNT64>(Bitboard b) {
b -= ((b>>1) & 0x5555555555555555ULL);
b = ((b>>2) & 0x3333333333333333ULL) + (b & 0x3333333333333333ULL);
b = ((b>>4) + b) & 0x0F0F0F0F0F0F0F0FULL;
b *= 0x0101010101010101ULL;
return int(b >> 56);
}
template<>
inline int count_1s<CNT64_MAX15>(Bitboard b) {
b -= (b>>1) & 0x5555555555555555ULL;
b = ((b>>2) & 0x3333333333333333ULL) + (b & 0x3333333333333333ULL);
b *= 0x1111111111111111ULL;
return int(b >> 60);
}
template<>
inline int count_1s<CNT32>(Bitboard b) {
unsigned w = unsigned(b >> 32), v = unsigned(b);
v -= (v >> 1) & 0x55555555; // 0-2 in 2 bits
w -= (w >> 1) & 0x55555555;
v = ((v >> 2) & 0x33333333) + (v & 0x33333333); // 0-4 in 4 bits
w = ((w >> 2) & 0x33333333) + (w & 0x33333333);
v = ((v >> 4) + v) & 0x0F0F0F0F; // 0-8 in 8 bits
v += (((w >> 4) + w) & 0x0F0F0F0F); // 0-16 in 8 bits
v *= 0x01010101; // mul is fast on amd procs
return int(v >> 24);
}
template<>
inline int count_1s<CNT32_MAX15>(Bitboard b) {
unsigned w = unsigned(b >> 32), v = unsigned(b);
v -= (v >> 1) & 0x55555555; // 0-2 in 2 bits
w -= (w >> 1) & 0x55555555;
v = ((v >> 2) & 0x33333333) + (v & 0x33333333); // 0-4 in 4 bits
w = ((w >> 2) & 0x33333333) + (w & 0x33333333);
v += w; // 0-8 in 4 bits
v *= 0x11111111;
return int(v >> 28);
}
template<>
inline int count_1s<CNT_POPCNT>(Bitboard b) {
#if !defined(USE_POPCNT)
return int(b != 0); // Avoid 'b not used' warning
#elif defined(_MSC_VER) && defined(__INTEL_COMPILER)
return _mm_popcnt_u64(b);
#elif defined(_MSC_VER)
return (int)__popcnt64(b);
#elif defined(__GNUC__)
unsigned long ret;
__asm__("popcnt %1, %0" : "=r" (ret) : "r" (b));
return ret;
#endif
}
#endif // !defined(BITCOUNT_H_INCLUDED)

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while(value)
{
value &= (value-1);
cnt++;
}

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