C实现二进制乘法

 1 /*
 2     二进制乘法
 3 */
 4 #include <stdio.h>
 5 #include <stdlib.h>
 6 #define LEN 64        //因子二进制位数的两倍，32位乘法结果不会超过64位
 7 
 8 int main()
 9 {
10     unsigned int a = 0x13131313;
11     unsigned int b = 0x23232323;
12     unsigned int p = 0x00000001;
13     unsigned int temp = 0;            
14     unsigned int flags;                //用于判断做加法时是否溢出
15     int i;
16     int rlt[LEN] ={0};                //结果数组
17     
18     for(i=0; i<LEN; i++)                //主循环
19     {
20         flags = 0;
21 
22         if(b&p)                        //判断是否需要做加法
23         {
24             flags = temp;
25             temp += a;
26         }
27 
28         rlt[i] = (int) temp & 1;    //最低位丢弃，并保存至数组
29         if(temp < flags)            //判断是否溢出
30             temp += 0x80000000;
31 
32         temp >>= 1;                    //右移结果
33         p <<= 1;
34     }
35 
36     i = LEN-1;
37     while(rlt[i] == 0) i--;            //丢弃结果前面的0
38     for(; i>=0; i--)                //打印结果
39         printf("%d", rlt[i]);
40 
41     printf("\n");
42     
43     return EXIT_SUCCESS;
44 }
45 #ifdef RESULT 
46 D:
47 cd Cprogram
48 gcc axb.c
49 (echo #ifdef RESULT & doskey /history & a.exe & echo #endif) >> ./axb.c
50 1010011110001110011101010101101011110100000011010010011001
51 #endif