求32位数中有几位非0位及最低非0位和最高非0位的方法

摘自http://www.xqbase.com/computer/struct_intro.htm

(1) 求一个32位数中有几位非零位的运算——Count32操作：

　
int Count32(unsigned long Arg) {
　Arg = ((Arg >> 1) & 0x55555555) + (Arg & 0x55555555);
　Arg = ((Arg >> 2) & 0x33333333) + (Arg & 0x33333333);
　Arg = ((Arg >> 4) & 0x0f0f0f0f) + (Arg & 0x0f0f0f0f);
　Arg = ((Arg >> 8) & 0x00ff00ff) + (Arg & 0x00ff00ff);
　return (Arg >> 16) + (Arg & 0x0000ffff);
}
　
(2) 求最低位非零位是第几位的运算——Lsb32操作(LSB = Least Significant Bit)：
　
int Lsb32(unsigned long Arg) {
　int RetVal = 31;
　if (Arg & 0x0000ffff) { RetVal -= 16; Arg &= 0x0000ffff; }
　if (Arg & 0x00ff00ff) { RetVal -= 8; Arg &= 0x00ff00ff; }
　if (Arg & 0x0f0f0f0f) { RetVal -= 4; Arg &= 0x0f0f0f0f; }
　if (Arg & 0x33333333) { RetVal -= 2; Arg &= 0x33333333; }
　if (Arg & 0x55555555) RetVal -=1;
　return RetVal;
}
　
(3) 求最高位非零位是第几位的运算——Msb32操作(MSB = Most Significant Bit)：
　
int Msb32(unsigned long Arg) {
　int RetVal = 0;
　if (Arg & 0xffff0000) { RetVal += 16; Arg &= 0xffff0000; }
　if (Arg & 0xff00ff00) { RetVal += 8; Arg &= 0xff00ff00; }
　if (Arg & 0xf0f0f0f0) { RetVal += 4; Arg &= 0xf0f0f0f0; }
　if (Arg & 0xcccccccc) { RetVal += 2; Arg &= 0xcccccccc; }
　if (Arg & 0xaaaaaaaa) RetVal += 1;
　return RetVal;
}