Square-and-multiply algorithm for efficient exponentiation

sm.cpp

long squareAndMultiply(long base, unsigned short power)
{
    // x^0 = 1
    if (! power) return 1;

    // x^1 = x
    if (power == 1) return base;

    // if power is odd
    if (power % 2)
    {
      // Make the power an even number by moving
      // one multiplication out of the power and
      // in front of the equation, then call the
      // the function recursively, reducing x^n
      // to (x^2)^n/2, since succesive powers are
      // multiplied in a mathematical equation
      return base * squareAndMultiply(base*base,(power-1)/2);
    }

    // else if power is even, do same as
    // for odd but without the need to make
    // it even anymore
    else return squareAndMultiply(base*base,power/2);
}