用加法模拟乘法

    /* 
         用加法模拟乘法 
     */  
      
    #include <stdio.h>  
    #include <stdlib.h>  
    //#define T(O,R,N,i) (N&(1<<i)) && (O+=(R<<i))  
    #define T(o,a,b,i) (b&1<<i) && (o+=a<<i)  
    int simulateMutiply(int a,int b)  
    {  
        int out=0;  
        T(out, a, b, 0);  
        T(out, a, b, 1);  
        T(out, a, b, 2);  
        T(out, a, b, 3);  
        T(out, a, b, 4);  
        T(out, a, b, 5);  
        T(out, a, b, 6);  
        T(out, a, b, 7);  
        T(out, a, b, 8);  
        T(out, a, b, 9);  
        T(out, a, b, 10);  
        T(out, a, b, 11);  
        T(out, a, b, 12);  
        T(out, a, b, 13);  
        T(out, a, b, 14);  
        T(out, a, b, 15);  
        T(out, a, b, 16);  
        T(out, a, b, 17);  
        T(out, a, b, 18);  
        T(out, a, b, 19);  
        T(out, a, b, 20);  
        T(out, a, b, 21);  
        T(out, a, b, 22);  
        T(out, a, b, 23);  
        T(out, a, b, 24);  
        T(out, a, b, 25);  
        T(out, a, b, 26);  
        T(out, a, b, 27);  
        T(out, a, b, 28);  
        T(out, a, b, 29);  
        T(out, a, b, 30);  
        T(out, a, b, 31);  
        return out;  
      
    }  
    int main(void) {  
        printf("%d 
",simulateMutiply(26,3));  
        return EXIT_SUCCESS;  
    }  

转自：http://blog.csdn.net/shandianling/article/details/8785481