package rebelsky.computation;

import java.math.BigDecimal;

/**
 * More fun computations!
 *
 * @author Samuel A. Rebelsky
 * @version 1.0 of October 2004
 */
public class Computer
{

// +--------+--------------------------------------------------
// | Fields |
// +--------+

	/**
	 * The number of "steps" done in the recent computation.
	 */
	long steps;

// +---------------------+-------------------------------------
// | Bookkeeping Methods |
// +---------------------+

	/**
	 * Reset the number of steps taken to 0.
	 */
	public void reset()
	{
		this.steps = 0;
	} // reset()

	/**
	 * Get a count of the number of steps since the last
	 * call to reset.
	 */
	public long steps()
	{
		return this.steps;
	} // steps()


// +---------------------+-------------------------------------
// | Computation Methods |
// +---------------------+

	/**
	 * Compute x^y iteratively.
	 */
	public BigDecimal expi(BigDecimal x, long y)
	{
		BigDecimal result = new BigDecimal(1.0);
		for (long i = 0; i < y; i++) {
			result = result.multiply(x);
			++this.steps;
		}
		return result;
	} // expi(BigDecimal, long)

	/**
	 * Compute x^y using clever recursion.
	 */
	public BigDecimal expr(BigDecimal x, long y)
	{
		if (y == 0)
			return new BigDecimal(1.0);
		else if (2* (y / 2) != y) { // y is odd 
			++this.steps;
			return x.multiply(expr(x, y-1));
		}
		else {
			BigDecimal tmp = expr(x, y/2);
			++this.steps;
			return tmp.multiply(tmp);
		}
	} // expr(BigDecimal, long)
} // class Computer