linux c 实现大数相乘

 

#include <stdio.h>
#include <string.h>
#include <math.h>
#include <stdbool.h>

#define MAX_LENGTH 128
#define ASSIST_LENGTH 19

int main(int argc, char **argv)
{
    unsigned long long data[MAX_LENGTH] = {0}, tmp = 0;
    int i = 0, j = 0, o_len = MAX_LENGTH - ASSIST_LENGTH;
    bool c_flag = true;

    if (argc < 3)
    {
        printf("argument error\n");
        return -1;
    }

    if (strlen(argv[1]) > o_len)
    {
        printf("out of range\n");
        return -1;
    }
    
    if (strlen(argv[2]) > 19)
    {
        printf("out of range\n");
        return -1;
    }
    
    tmp = atoll(argv[2]);

    if (9223372036854775807ULL == tmp && ('8' == argv[2][18] || '9' == argv[2][18]))
    {
        printf("out of range\n");
        return -1;
    }

    for (i = strlen(argv[1])-1; i >= 0; i--)
    {
        data[j] = argv[1][i] - 48;
        j++;
    }

    for (i = o_len - 1; i >= 0; i--)
    {
        if (c_flag && 0 == data[i])
        {
            continue;
        }

        c_flag = false;
        printf("%llu", data[i]);
    }
    printf(" * %llu\n", tmp);

    for (i = 0; i < o_len; i++)
    {
        if (0 == data[i])
        {
            continue;
        }
        
        data[i] *= tmp;
    }

    for (i = 0; i < o_len; i++)
    {
        if (0 == data[i])
        {
            continue;
        }
        
        tmp = data[i];
        
        for (j = ASSIST_LENGTH-1; j >= 1; j--)
        {
            data[i+j] += (tmp / (unsigned long long)pow(10,j));
            tmp %= (unsigned long long)pow(10,j);
        }
        
        data[i] %= 10;
    }

    c_flag = true;
    for (i = MAX_LENGTH - 1; i >= 0; i--)
    {
        if (c_flag && 0 == data[i])
        {
            continue;
        }

        c_flag = false;
        printf("%llu", data[i]);
    }
    printf("\n");
    
    return 0;
}

 

实现了任意大数与 2^64-1以下的数相乘，

两个任意大数可以将其中一个拆分成多个因子，

两个大数质数暂未考虑