/*
 * File:
 *   expt.c
 * Author:
 *   Samuel A. Rebelsky
 * Version:
 *   1.0 of March 2003
 * Summary:
 *   An implementation of the logarithmic time exponentiation
 *   procedure.
 */

#include "expt.h"

/*********************************************************************
 * Exported Procedures *
 ***********************/

double expt(double val, int power) {
  double result = 1;
  double x = val;
  int n = power;
  /* result*x^n == val^power */
  while (n > 0) {
    if (n % 2 == 0) {
      x = x*x;
      n = n/2;
      /* result*x^n == val^power */
    }
    else {
      result = result * x;
      n = n-1;
      /* result*x^n == val^power */
    }
  } /* while */
  /* result*x^n == val^power */
  /* n = 1. */
  /* Therefore, result = val^power. */
  return result;
} /* expt(double, int) */