LeetCode Divide Two Integers

class Solution {
public:
int divide(int dividend, int divisor) {
bool aneg = dividend < 0;
bool bneg = divisor < 0;
unsigned int a = dividend;
unsigned int b = divisor;
if (aneg) a = ~(a - 1);
if (bneg) b = ~(b - 1);
unsigned int oa = a, ob = b;
if (b > a || a == 0) return 0;

unsigned int abits = 0, bbits = 0;
while (a) a>>=1, abits++;
while (b) b>>=1, bbits++;
a = oa, b = ob;
unsigned int a_high_bit = 1<<(abits-1);
unsigned int mask = a_high_bit;
for (int i=bbits-1; i>0; i--) {
mask = a_high_bit | (mask>>1);
}
unsigned int res = 0;
unsigned int r_mask = 1<<(abits - bbits);
b = b<<(abits - bbits);
while (r_mask) {
if ((mask & a) >= (mask & b)) {
res |= r_mask;
a = a - b;
}
mask = (mask>>1)|a_high_bit;
r_mask>>=1;
b>>=1;
}
if (aneg^bneg)
return -res;
else
return res;
}
};

犹记得当年计组的时候手工做过，如果不用long的话，在有符号和无符号之间转换要非常小心

参考：

　　http://blog.csdn.net/feiyangyangfei/article/details/9214107