[racket] FW: q about code for partitions

It looks like "partitions2.rkt" ends up calling a contract-wrapped
variant of `exact-zero?`. If I change `ref!` to

 (define (ref! n thnk)
   (let ([v (vector-ref cache n)])
     (if (zero? v)
         (let ([new-v (thnk)])
           (vector-set! cache n new-v)
           new-v)
         v)))

then "partitions2.rkt" is much faster.

At Sat, 28 Jun 2014 12:06:34 +0200, Jens Axel Søgaard wrote:
> Hi,
> 
> I have converted your code to Typed Racket and made two versions.
> The first version use a hash as cache and the second version us a vector.
> 
> Timings show that the vector version is 1.5 to 2 times slower than the
> hash version.
> 
> I don't understand this. Is there anything that can be done to improve it?
> 
> The two versions can be seen here in color:
> 
>     http://pasterack.org/pastes/12166
>     http://pasterack.org/pastes/16085
> 
> They are also attached.
> 
> I used (time (begin (partitions 50000) 0)) as benchmark.
> 
> 
> 
> 
> 2014-06-28 9:54 GMT+02:00 Jos Koot <jos.koot at gmail.com>:
> > Sorry, forgot to post the following to the users list.
> >
> > Hi,
> > count partitions, much faster and exact.
> > You may want to put the hash or part of it within function p such as to
> > avoid spllling much memory.
> > Jos
> >
> > #lang racket
> >
> > (require math/number-theory)
> >
> > (define p-hash (make-hash '((0 . 1))))
> >
> > (define (p n)
> >  (hash-ref! p-hash n
> >   (λ ()
> >    (+
> >     (let loop ((k 1) (m (sub1 n)) (s 0))
> >      (if (< m 0) s
> >       (loop (add1 k) (- m (add1 (* 3 k))) (if (odd? k) (+ s (p m)) (- s (p
> > m))))))
> >     (let loop ((k -1) (m (- n 2)) (s 0))
> >       (if (< m 0) s
> >        (loop (sub1 k) (+ m (* 3 k) -2) (if (odd? k) (+ s (p m)) (- s (p
> > m))))))))))
> >
> > (time (for ((n (in-range 0 1000))) (p n)))
> > (time (for ((n (in-range 0 1000))) (partitions n)))
> > (void (time (p 10000)))
> >
> > (for/and ((n (in-range 0 1000))) (= (partitions n) (p n)))
> >
> > (read-line)
> >
> > ; results with racket:
> > ; cpu time: 16 real time: 16 gc time: 0
> > ; cpu time: 8845 real time: 8845 gc time: 111
> > ; cpu time: 577 real time: 578 gc time: 0
> > ; #t
> >
> >
> >
> > ____________________
> >   Racket Users list:
> >   http://lists.racket-lang.org/users
> 
> 
> 
> -- 
> --
> Jens Axel Søgaard
> 
> 
> ------------------------------------------------------------------------------
> [application/octet-stream "partitions2.rkt"] [~/Desktop & open] [~/Temp & open]
> 
> 
> ------------------------------------------------------------------------------
> [application/octet-stream "partitions1.rkt"] [~/Desktop & open] [~/Temp & open]
> ____________________
>   Racket Users list:
>   http://lists.racket-lang.org/users