利用位运算实现加减乘除

参考http://www.cnblogs.com/dandingyy/archive/2012/10/29/2745570.html 和 http://blog.csdn.net/hackbuteer1/article/details/7390093

面试必备。

#include<iostream>
#include<cstdlib>
using namespace std;
//递归版本的加法实现
int Add(int a, int b)
{
return b ? Add(a^b, (a&b)<<1) : a;
/*
if(b)
return plus_rec(a^b, (a&b)<<1);
else
return a;
*/
}
//该为迭代版本
int Add_iter(int a, int b)
{
int ans;
while(b)
{
ans = a^b;
b = (a&b)<<1;
a = ans;
}
return ans;
}
//求a的相反数：将各位取反加一
int negative(int a)
//get -a
{
return Add(~a, 1);
}
int Minus(int a, int b)
{
return Add(a, negative(b));
}
//正数乘法
int Multi(int a, int b)
{
int ans = 0;
while(b)
{
if(b&1)
ans = Add(ans, a);
a = a << 1;
b = b >> 1;
}
return ans;
}
//正数除法
int Divide(int a, int b)
{
int coun = 0;
while(a >= b)
{
a = Minus(a, b);
coun = Add(coun, 1);
}
return coun;
}
//判断是否是负数，0，正数
int isneg(int a)
{
return a & 0x8000;
}
int iszero(int a)
{
return !(a & 0xFFFF);
}
int ispos(int a)
{
return (a&0xFFFF) && !(a&0x8000);
}
//处理负数的乘法和除法
int My_Multi(int a, int b)
{
if(iszero(a) || iszero(b))
return 0;
if(isneg(a))
{
if(isneg(b))
return Multi(negative(a), negative(b));
else
return negative(Multi(negative(a), b));
}else if(isneg(b))
return negative(Multi(a, negative(b)));
else
return Multi(a, b);
}
int My_Divide(int a, int b)
{
if(iszero(b))
{
cout << "Error!" << endl;
exit(1);
}
if(iszero(a))
return 0;
if(isneg(a))
{
if(isneg(b))
return Divide(negative(a), negative(b));
else
return negative(Divide(negative(a), b));
}else if(isneg(b))
return negative(Divide(a, negative(b)));
else
return Divide(a, b);
}
int main(int argc, char **argv)
{
int a = 5;
int aa = -5;
int b = 3;
int bb = -3;
int c = 15;
cout << Add(a, b) << endl;
cout << Add(a, bb) << endl;
cout << Minus(a, b) << endl;
cout << Minus(b, a) << endl;
cout << Multi(a, b) << endl;
cout << My_Multi(aa, b) << endl;
cout << Divide(c, a) << endl;
return 0;
}