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## 求二进制数中1的个数

Wu Yudong    July 24, 2016     Algorithm   723

int Count1(unsigned int v)
{
int num = 0;
while (v) {
if (v % 2 == 1) {
num++;
}
v = v / 2;
}
return num;
}

int Count2(unsigned int v)
{
unsigned int num = 0;
while (v) {
num += v & 0x01;
v >>= 1;
}
return num;
}

int Count3(unsigned int v)
{
int num = 0;
while (v) {
v &= (v - 1);
num++;
}
return num;
}

int Count4(unsigned int v)
{
int num = 0;
switch (v) {
case 0x0:
num = 0;
break;
case 0x1:
case 0x2:
case 0x4:
case 0x8:
case 0x10:
case 0x20:
case 0x40:
case 0x80:
num = 1;
break;
case 0x3:
case 0x6:
case 0xc:
case 0x18:
case 0x30:
case 0x60:
case 0xc0:
num = 2;
break;
//...
}
return num;
}

int countTable[256] = {
0, 1, 1, 2, 1, 2, 2, 3, 1, 2, 2, 3, 2, 3, 3, 4,
1, 2, 2, 3, 2, 3, 3, 4, 2, 3, 3, 4, 3, 4, 4, 5,
1, 2, 2, 3, 2, 3, 3, 4, 2, 3, 3, 4, 3, 4, 4, 5,
2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6,
1, 2, 2, 3, 2, 3, 3, 4, 2, 3, 3, 4, 3, 4, 4, 5,
2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6,
2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6,
3, 4, 4, 5, 4, 5, 5, 6, 4, 5, 5, 6, 5, 6, 6, 7,
1, 2, 2, 3, 2, 3, 3, 4, 2, 3, 3, 4, 3, 4, 4, 5,
2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6,
2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6,
3, 4, 4, 5, 4, 5, 5, 6, 4, 5, 5, 6, 5, 6, 6, 7,
2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6,
3, 4, 4, 5, 4, 5, 5, 6, 4, 5, 5, 6, 5, 6, 6, 7,
3, 4, 4, 5, 4, 5, 5, 6, 4, 5, 5, 6, 5, 6, 6, 7,
4, 5, 5, 6, 5, 6, 6, 7, 5, 6, 6, 7, 6, 7, 7, 8
};
int Count5(BYTE v)
{
return countTbale[v];
}