Divide large decimal using shift operator

Question

How to write a program in c to split a large number using the shift operator?

For example, we need to break a large number, for example 12345678, into two smaller digits 1234 and 5678, using only bit shifting operations and not using the usual n = n * 10 and n = n% 10. How will you do this?

Answer 1

You can use the standard long division algorithm and call it 12345678 and 10000. If you want to optimize it to divide only by 10000, first evaluate it manually for b == 10000.

void div(int a, int b) {
    int d, res;
    d = 1;
    res = 0;
    while (b > 0 && b < a) {
        b <<= 1;
        d <<= 1;
    }

    do {
        if (a >= b) {
            a -= b;
            res += d;
        }
        b >>= 1;
        d >>= 1;
    } while (d);

    printf("Result: %d, reminder: %d\n", res, a);
}

int main() {
    div(12345678, 10000);
}

Answer 2

BCD, , .

BCD Conversion, .