[racket] translate from Racket to Common Lisp

Thanks!

Sometimes, a x3 difference means that we're missing a straightforward
opportunity in performance, and that was the case here. The Racket
program spent most of its time in generic `/' by pessimistically
expecting a non-integer result.

I've adjusted the JIT to optimistically compute and check a fixnum
result for a division of fixnums, and then the example runs about four
times as fast on my machine:

 Old Racket:                12589 msec
 New Racket:                 3850 msec 
 Racket with `quotient':     3851 msec  [old or new is the same]
 SBCL:                       5553 msec
 SBCL, unsafe fixnum:        2692 msec
 New Racket, in module:      2823 msec
 Racket, unsafe fixnum:      2405 msec  [uses `fxquotient']

At Sun, 4 Nov 2012 15:54:51 +0000 (UTC), daniel rupistraliz wrote:
> 
> 
>  racket: 
> Welcome to Racket v5.2.1.
> > (define (cycle-length n)
>     (cond
>       [(= n 1)
>        1]
>       [(odd? n)
>        (add1 (cycle-length (add1 (* 3 n))))]
>       [(even? n)
>        (add1 (cycle-length (/ n 2)))]))
> 
> (time (for ([i (in-range 1 1000000)])
>           (cycle-length i)))
> > 
> cpu time: 15016 real time: 15018 gc time: 0
> 
> sbcl:
> 
> (defun cycle-length(n)
>  (cond ((= n 1) 1)
>        ((oddp n) (1+ (cycle-length (1+ (* 3 n)))))
>        ((evenp n) (1+ (cycle-length (/ n 2))))))
> 
> 
> * (time (loop for i from 1 to 1000000 do (cycle-length i)))
> 
> Evaluation took:
>   6.192 seconds of real time
>   6.192387 seconds of total run time (6.192387 user, 0.000000 system)
>   100.00% CPU
>   14,496,643,427 processor cycles
>   0 bytes consed
> 
> 
> With optimizations:
> 
> (defun cycle-length(n)
>   (declare (fixnum n)
> 	   (ftype (function (fixnum) fixnum) cycle-length)
> 	   (optimize (speed 3) (safety 0) (compilation-speed 0)))
>   (cond ((= n 1) 1)
> 	((oddp n) (the fixnum (1+ (cycle-length
> 				   (the fixnum (1+ (the fixnum (* 3 n))))))))
> 	((evenp n) (cycle-length (the fixnum (/ n 2))))))
> 
> CL-USER> (time (loop for i from 1 to (expt 10 6) do (cycle-length i)))
> Evaluation took:
>   3.515 seconds of real time
>   3.524220 seconds of total run time (3.524220 user, 0.000000 system)
>   100.26% CPU
>   8,228,949,701 processor cycles
>   33,008 bytes consed
> 
> So racket = 15 seconds
>     sbcl  =  6 seconds
> sbcl optimized = 3.5 seconds.
> 
> 
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