Allegro CL Floating Point

[maida@cs.psu.edu (Anthony Maida)]

We need to do fast floating point in Lisp. We have benchmarked
a C program and a Lisp program. Both programs call an exponential
function and a trig function 250,000 times.

The C program runs in under 10 seconds. The Lisp program takes
at least 50 seconds. We can't understand why there should be
such a discrepancy. Can anyone replicate this and explain the
discrepancy? We are using the following version of Allegro 

            3.1.beta.22 [Sun4] (6/8/89)


Anthony Maida
maida@cs.psu.edu

;;;================================================================
;;; C program

#include <math.h>

#define cnt 500

main()
{
	int i,j;
	double b;

	for (i=0; i<cnt; i++)
	   for (j=0; j<cnt; j++) {
	      b = exp(-.3);
	      b = cos(-.51);
	      }
	}

;;;================================================================
;;; Lisp program

(defun speed (cnt)
   (declare (optimize (speed 3) (safety 0)))
   (declare (fixnum cnt))
   (let ((b 0.0))
   (declare (single-float b))
   (declare (:explain :calls :types))
   (dotimes (i cnt)
      (declare (fixnum i))
      (dotimes (j cnt)
	 (declare (fixnum j))
	 (setf b (exp -.3))
	 (setf b (cos .51))))))

(speed 500)