（超强）反转一个字节 和 判断32位整数二进制中1的个数 的算法

tianbianlan

unsigned char reverse8( unsigned char c ) { c = ( c & 0x55 ) << 1 | ( c & 0xAA ) >> 1; c = ( c & 0x33 ) << 2 | ( c & 0xCC ) >> 2; c = ( c & 0x0F ) << 4 | ( c & 0xF0 ) >> 4; return c; }
unsigned long func(unsigned long x) { x = (x & 0x55555555UL) + ((x >> 1) & 0x55555555UL); x = (x & 0x33333333UL) + ((x >> 2) & 0x33333333UL); x = (x & 0x0f0f0f0fUL) + ((x >> 4) & 0x0f0f0f0fUL); x = (x & 0x00ff00ffUL) + ((x >> 8) & 0x00ff00ffUL); x = (x & 0x0000ffffUL) + ((x >> 16) & 0x0000ffffUL); return x; }