一道面试题（如何解决）

一道面试题（怎么解决）
写一个函数将一个DWORD类型,2进制,位数为1的个数返回出来？
用什么方法写啊，有那位高手指导一下？

[解决办法]

C/C++ code

//假定你的环境下unsigned int 为32位,否则换个unsigned long也行char table16[16] = { 0,1,1,2, 1,2,2,3, 1,2,2,3, 2,3,3,4} ;char table256[256];void    SetData(){    for (int i = 0; i < 16; i++)        for (int j = 0; j < 16; j++)            table256[i*16+j] = table16[i] + table16[j];}unsigned int bitcount32_1(unsigned int 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; }unsigned int bitcount32_2(unsigned int x){    x = x - ((x >> 1) & 0x55555555UL);      x = (x & 0x33333333UL) + ((x >> 2) & 0x33333333UL);          x = (x + (x >> 4)) & 0x0f0f0f0fUL;      x += x >> 8;     x += x >> 16;          return x & 0x3f; }unsigned int bitcount32_3(unsigned int x){    return table16[x&0xf]+table16[(x>>4)&0xf]+table16[(x>>8)&0xf]+table16[(x>>12)&0xf] +        table16[(x>>16)&0xf]+table16[(x>>20)&0xf]+table16[(x>>24)&0xf]+table16[(x>>28)&0xf];}unsigned int bitcount32_4(unsigned int x){    return table256[x&0xff] + table256[(x>>8)&0xff]+        table256[(x>>16)&0xff] + table256[(x>>24)&0xff];}