package Fibonacci2;

/**
 * Slow Fibonacci Number Calculator.
 *
 * @author Wayne Eberly
 */

public class SFibonacci {

  /**
  * Computes a specified Fibonacci number as a long integer by a direct
  * application of the recursive definition.
  *
  * <p>
  *  This method is too slow to be used in practice. It is provided
  *  to facilitate testing of more efficient methods.
  * </p>
  * 
  * <p>
  *  <strong>Precondition:</strong>
  *       <code>i</code> is a nonnegative integer.<br />
  *  <strong>Postcondition:</strong>
  *       Value returned is the <code>i</code><sup>th</sup>
  *       Fibonacci number.
  * </p>
  * 
  * @param i Index of the Fibonacci number to be calculated
  * @return  The ith Fibonacci number
  * @throws IllegalArgumentException If the input integer is negative
  *
  */
  protected static long fib(int i) {
    if (i<0) {
      throw new IllegalArgumentException("Negative Input: " + i);
    } else {                          // i >= 0
      if (i==0) {
        return 0;
      } else {                        // i >= 1
	if (i==1) {
	  return 1;
	} else {                      // i >= 2
	  return fib(i-1) + fib(i-2);
	}
      }
    }
  }

}