#include <string.h>
#include <stdio.h>
#define len1 (8)
#define len2 (4)
int ncmp(unsigned char const *a, unsigned char const *b, int n)
{
    int i;
    for (i = n - 1; i >= 0; i--)
        if (a[i] > b[i])
            return 1;
        else if (a[i] < b[i])
            return -1;
    if (i < 0)
        return 0;
}
int nsub(unsigned char *a, unsigned char *b, int n)
{
    int i, carry = 0;
    for ( i = 0; i < n; i++) {
        a[i] -= carry;
        if (a[i] < b[i]) {
            a[i] = 0xff - b[i] + 0x01 + a[i];
            carry = 1;
        } else
            a[i] -= b[i];
    }
    return 0;
}
int nshr(unsigned char *a, int n)
{
    int i;
    for (i = n - 1; i > 0; i--) {
        a[i] <<= 1;
        a[i] |= (a[i - 1] >> 7);
    }
    a[0] <<= 1;
}
int div(unsigned char a[], unsigned char b[], unsigned char c[])
{
    unsigned char x[len2];    
    int i, j;
    memset(x, 0, sizeof(x));
    memset(c, 0, sizeof(unsigned char) * len1);

    for (i = 0; i < 8 * len1; i++) {
        nshr(x, len2);
        nshr(c, len1);
        x[0] |= (a[len1 - 1] >> 7);
        if (ncmp(x, b, len2) >= 0) {
            c[0] |= 1;
            nsub(x, b, len2);
        }
        nshr(a, len1);
    }
    memcpy(a, x, sizeof(x));
}
int main()
{
    unsigned char a[8], b[8], c[8];
    unsigned long long *a_l = (unsigned long long *)a;
    unsigned long long *b_l = (unsigned long long *)b;
    unsigned long long *c_l = (unsigned long long *)c;
    *a_l = 1124141234;
    *b_l = 123;
    div(a, b, c);
    printf("a = %ld\n", *a_l);
    printf("c = %ld\n", *c_l);
    return 0;
}

------解决方案--------------------

C/C++ code

/*
 a[] 被除数
 b[] 除数
 c[] 商
 余数放回a[]里面
*/
int div(unsigned char a[], unsigned char b[], unsigned char c[])