[racket] FW: q about code for partitions

Given that partitions2.rkt is written in TR, it shouldn't have to go
through a contract boundary to use `exact-zero?` (which is also written
in TR). The contract profiler does not observe any time spent in
contracts, which supports that hypothesis.

How did you discover that `exact-zero?` was wrapped? I'm wondering
whether we looked at different versions of the code (I ran the version
Jens attached to his email), or whether there's a bug in the contract
profiler.

Vincent



At Sun, 29 Jun 2014 07:47:24 +0100,
Matthew Flatt wrote:
> 
> 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
> 
> ____________________
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