(defconstant DIM 512)

(defvar matrix_1 (make-array (list DIM DIM) :element-type '(unsigned-byte 16)))
(defvar matrix_2 (make-array (list DIM DIM) :element-type '(unsigned-byte 16)))
(defvar matrix_3 (make-array (list DIM DIM) :element-type '(unsigned-byte 16)))

(defun foo (a1 a2 r)
  (declare (optimize (speed 3) (safety 0))
	   (type (simple-array (unsigned-byte 16) (512 512)) a1)
	   (type (simple-array (unsigned-byte 16) (512 512)) a2)
	   (type (simple-array (unsigned-byte 16) (512 512)) r))
  (dotimes (x DIM) (declare (fixnum x))
	   (dotimes (y DIM) (declare (fixnum y))
		    (setf (aref a1 x y)
			  12)))
  (dotimes (x DIM) (declare (fixnum x))
	   (dotimes (y DIM) (declare (fixnum y))
		    (setf (aref a2 x y)
			  12)))
  (dotimes (x DIM) (declare (fixnum x))
	   (dotimes (y DIM) (declare (fixnum y))
		    (setf (aref r x y)
			  0)))
  (dotimes (x DIM) (declare (fixnum x))
	   (dotimes (y DIM) (declare (fixnum y))
		    (dotimes (z DIM) (declare (fixnum z))
			     (setf (aref r x y) (+ (aref r x y) (* (aref a1 z y) (aref a2 x z))))))))