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[Caml-list] what is the functional way to solve this problem?
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Date: -- (:)
From: Michal Moskal <malekith@p...>
Subject: Re: [Caml-list] what is the functional way to solve this problem?
On Wed, Oct 08, 2003 at 04:48:09PM +0200, Pierre Weis wrote:
> Hi Michal,
> 
> [...]
> > Key points of my implementation:
> [...]
> > 3. It doesn't use Scanf. For such linear task as this Scanf takes 10 or
> >    more times to parse input then actual computations.
> [...]
> > -- 
> > : Michal Moskal :: http://www.kernel.pl/~malekith : GCS {C,UL}++++$ a? !tv
> > : When in doubt, use brute force. -- Ken Thompson : {E-,w}-- {b++,e}>+++ h
> 
> I'm sorry to report that I was so puzzled by your number 3) key point,
> that I tested your code and a ``purely scanf'' version to see this
> ``10 or more times to parse'' behaviour; I didn't notice any runtime
> difference between the two (native code compiled) versions. Am I
> missing something ?

Hm, with your version it's only 3 times slower:

-rw-r--r--    1 malekith users     1909887 Oct  8 18:02 /shm/d2

./statsf < /shm/d2 > /dev/null  0.31s user 0.01s system 103% cpu 0.308
total
./stats < /shm/d2 > /dev/null  0.10s user 0.00s system 155% cpu 0.064
total

However, your code is not correct:

> Could you please try to use the following version of your read
> function, and report the runtime difference between your hand written
> code ?
> 
> (BTW, I compiled the 2 programs using ocamlopt -unsafe -inline 9)
> 
> let read () =
>   try
>     Scanf.bscanf Scanf.Scanning.stdib " %c" (function
>     | 'D' ->
>         Scanf.bscanf Scanf.Scanning.stdib " %d %d %s"
----------------------------------------------------^^

It should be [^\n], as filenames can contain spaces. In this case:

./statsf < /shm/d2 > /dev/null  1.56s user 0.04s system 96% cpu 1.654
total

Well, it's 15 times slower.

All tests were run on athlon 1.56GHz, under pld-linux, ocaml 3.07,
ocamlopt -unsafe -inline 9.

-- 
: Michal Moskal :: http://www.kernel.pl/~malekith : GCS {C,UL}++++$ a? !tv
: When in doubt, use brute force. -- Ken Thompson : {E-,w}-- {b++,e}>+++ h

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