Subject: Re: macro question From: Erik Naggum <email@example.com> Date: Fri, 08 Mar 2002 18:32:48 GMT Newsgroups: comp.lang.lisp Message-ID: <firstname.lastname@example.org> * Rolf Wester <email@example.com> | My point is performance. Are you quite sure about that? | My function is: | | (defun maxwell-v (v temp m) | (let ((c1 (* 4.0d0 dpi (expt (/ m (* 2.0d0 dpi +kB+ temp)) 1.5d0))) | (c2 (/ (* -1.0d0 m) (* 2.0d0 +kB+ temp)))) | (* c1 v v(exp (* v v c2))))) | | I don't want to calculate c1 and c2 every time I call the function with | only v different than in the other calls. Common Lisp programmers generally do this with memoization. Several general wrappers exist, but if you make a lot of calls in a row with only v varying, as you say, here's a simple solution that computes c1 and c2 only when temp and m is different from those in the previous call. It would also be natural to declare some types if you want more performance: (defun maxwell-v (v temp m) (declare (optimize (speed 3)) (double-float v temp m)) (let ((memo (load-time-value (vector nil nil nil nil)))) (declare (simple-vector memo)) (unless (and (eq (svref memo 0) temp) (eq (svref memo 1) m)) (setf (svref memo 0) temp) (setf (svref memo 1) m) (setf (svref memo 2) (* 4.0d0 dpi (expt (/ m (* 2.0d0 dpi +kB+ temp)) 1.5d0))) (setf (svref memo 3) (/ (* -1.0d0 m) (* 2.0d0 +kB+ temp)))) (* v v (the double-float (svref memo 2)) (exp (* v v (the double-float (svref memo 3))))))) This _should_ be faster than calling a closure. /// -- In a fight against something, the fight has value, victory has none. In a fight for something, the fight is a loss, victory merely relief.