Making a square() function without x*x in C++

Question

I am self-studying C++ and the book \"Programming-Principles and Practices Using C++\" by Bjarne Stroustrup. One of the \"Try This\" asks this:

Implement square() wi

Answer 1

Mats Petersson stole the idea out of my head even before I thought to think it.

#include 

template 
T square(T x) {
    if(x < 0) x = T(0)-x;
    T sum{0}, s{x};
    while(s) {
        if(s & 1) sum += x;
        x <<= 1;
        s >>= 1;
    }
    return sum;
}

int main() {
    auto sq = square(80);
    std::cout << sq << "\n";
}