How can I perform multiplication without the '*' operator?

Question

I was just going through some basic stuff as I am learning C. I came upon a question to multiply a number by 7 without using the * operator. Basically it\'s like this

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Answer 1

@Wang, that's a good generalization. But here is a slightly faster version. But it assumes no overflow and a is non-negative.

int mult(int a, int b){
    int p=1;
    int rv=0;
    for(int i=0; a >= p && i < 31; i++){
        if(a & p){
            rv += b;
        }
        p = p << 1;
        b = b << 1;
    }

    return rv;
}

It will loop at most 1+log_2(a) times. Could be faster if you swap a and b when a > b.