STINNER Victor <vstin...@python.org> added the comment:
> Mr. Stinner, in what way would int.bit_count() be beneficial to me? I found https://www.chessprogramming.org/Population_Count when I investigated the C implementation of _Py_popcount32(), which is used by int.bit_count(). I read it when I tried to document this surprising code: --- x = x - ((x >> 1) & 0x55555555); x = (x & 0x33333333) + ((x >> 2) & 0x33333333); x = (x + (x >> 4)) & 0x0F0F0F0F; return (uint32_t)((uint64_t)x * (uint64_t)0x01010101) >> 24; --- I reformatted it as: --- // 32-bit SWAR (SIMD Within A Register) popcount // Binary: 0 1 0 1 ... const uint32_t M1 = 0x55555555; // Binary: 00 11 00 11. .. const uint32_t M2 = 0x33333333; // Binary: 0000 1111 0000 1111 ... const uint32_t M4 = 0x0F0F0F0F; // 256**4 + 256**3 + 256**2 + 256**1 const uint32_t SUM = 0x01010101; // Put count of each 2 bits into those 2 bits x = x - ((x >> 1) & M1); // Put count of each 4 bits into those 4 bits x = (x & M2) + ((x >> 2) & M2); // Put count of each 8 bits into those 8 bits x = (x + (x >> 4)) & M4; // Sum of the 4 byte counts return (uint32_t)((uint64_t)x * (uint64_t)SUM) >> 24; --- ---------- _______________________________________ Python tracker <rep...@bugs.python.org> <https://bugs.python.org/issue43255> _______________________________________ _______________________________________________ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
