gistfile1.lisp

(defun fib (n)
  (declare (optimize (debug 0) (safety 0) (space 0) (speed 3))
           (fixnum n))
  (labels ((fib (n)
             (if (< n 2)
                 n
                 (let* ((fib/n-2
                         (let ((n (- n 2)))
                           (if (< n 2)
                               n
                               (the fixnum
                                    (+ (fib (1- n))
                                       (fib (- n 2)))))))
                        (fib/n-1
                         (let ((n (- n 1)))
                           (if (< n 2)
                               n
                               (the fixnum
                                    (+ fib/n-2
                                       (fib (- n 2))))))))
                   (the fixnum (+ fib/n-1
                                  fib/n-2))))))
    (declare (ftype (function (fixnum) fixnum) fib)
             (inline fib))
    (fib n)))

(fib 35)
;=> 9227465
#|------------------------------------------------------------|
Evaluation took:
  0.001 seconds of real time
  0.000000 seconds of total run time (0.000000 user, 0.000000 system)
  0.00% CPU
  1,439,217 processor cycles
  0 bytes consed
  
Intel(R) Core(TM)2 Duo CPU     P8600  @ 2.40GHz
 |------------------------------------------------------------|#