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.k...@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
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