16.1 Performance of Byte-Compiled Code

A byte-compiled function is not as efficient as a primitive function written in C, but runs much faster than the version written in Lisp. Here is an example:

(defun silly-loop (n) "Return time before and after N iterations of a loop." (let ((t1 (current-time-string))) (while (> (setq n (1- n)) 0)) (list t1 (current-time-string)))) => silly-loop (silly-loop 100000) => ("Fri Mar 18 17:25:57 1994" "Fri Mar 18 17:26:28 1994") ; 31 seconds (byte-compile 'silly-loop) => [Compiled code not shown] (silly-loop 100000) => ("Fri Mar 18 17:26:52 1994" "Fri Mar 18 17:26:58 1994") ; 6 seconds

In this example, the interpreted code required 31 seconds to run, whereas the byte-compiled code required 6 seconds. These results are representative, but actual results will vary greatly.