Multiplication of two integers using bitwise operators

Question

How can I multipy two integers using bitwise operators?

I found an implementation here. Is there a better way of implementing multiplication?

For example: 2

Answer 1

    #include
    void main()
    {
        int n, m, i, j, x, large, small, t1, m2, result, a1, a2, a3, c, c1, c2, r, r1, la, re;

        printf("Enter two numbers\n");
        scanf("%d%d", &n, &m);
        result = 0;

        if (n > m)
        {
            large = n;
            small = m;
        }
        else
        {
            large = m;
            small = n;
        }

        c = 0;

        while (small)
        {
            t1 = small;
            t1 &= 1;

            if (t1 == 1)
            {
                printf("\n %d", large);
                la = large;
                re = result;
                m2 = 0;
                r1 = 1;
                while (re || la || c)
                {
                    a2 = la;
                    a2 &= 1;
                    a3 = re;
                    a3 &= 1;

                    c1 = a2 & a3;
                    r = a3 ^ a2;

                    c2 =r & c;
                    r ^= c;
                    if (c1 || c2)
                        c = 1;
                    else
                        c = 0;

                    result &= ~r1;
                    x = r;
                    m2 >>= 1;
                    while (m2)
                    {
                        r <<= 1;
                        m2 >>= 1;
                    }

                    result |= r;
                    la >>= 1;
                    re >>= 1;
                    r1 <<= 1;
                    m2 = r1;
                }

            }
            large <<= 1;
            small >>= 1;

        }
        printf("\n%dX%d= %d\n", n, m, result);
    }