[Haskell-cafe] Re: newbie optimization question

[Dusan Kolar]

Hello all,

  just to compare the stuff, I get quite other results being on other 
OS. Thus, the result of C++ compiler may not be that interesting as I do 
not have the one presented below.

My machine:
Linux 2.6.23-ARCH #1 SMP PREEMPT Mon Oct 22 12:50:26 CEST 2007 x86_64 
Intel(R) Core(TM)2 CPU  6600 @ 2.40GHz GenuineIntel GNU/Linux

Compilers:
g++ --version
g++ (GCC) 4.2.2
Copyright (C) 2007 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

ghc --version
The Glorious Glasgow Haskell Compilation System, version 6.6.1

Measurement:
compiled with ghc -O2
time ./mainInteger
real    0m4.866s
user    0m4.843s
sys     0m0.020s

compiled with ghc -O2
time ./mainInt64
real    0m2.213s
user    0m2.210s
sys     0m0.003s

compiled with ghc -O2
time ./mainInt
real    0m1.149s
user    0m1.143s
sys     0m0.003s

compiled with g++ -O3
time ./mainC
real    0m0.271s
user    0m0.270s
sys     0m0.000s

I don't know what is the reason, but the difference between Int, Int64 
and Integer is not that dramatic as in example below, nevertheless, the 
difference between GHC and GNU C++ is very bad.... :-\

Dusan


Peter Hercek wrote:
> Derek Elkins wrote:
>>
>> Try with rem instead of mod.
>>
>> (What the heck is with bottom?)
>
> The bottom was there by error and I was lazy to redo
>  the tests so I rather posted exactly what I was
>  doing. I do not know the compiler that good to be
>  absolutely sure it cannot have impact on result
>  ... so I rather did not doctor what I did :-)
>
> Ok, rem did help quite a bit. Any comments why it is so?
>
> Here are summary of results for those interested. I run
>  all the tests once again. Haskell was about 13% slower
>  than C++.
>
> MS cl.exe options: /Ox /G7 /MD
> ghc options: -O2
>
> C++ version:  1.000; 0.984; 0.984
> Haskell version specialized to Int: 1.125; 1.125; 1.109
> Haskell version specialized to Integer: 8.781; 8.813; 8.813
> Haskell version specialized to Int64: 9.781; 9.766; 9.831
>
> The code:
>
> % cat b.hs
> module Main (divisors, perfect, main) where
> import Data.Int
>
> divisors :: Int -> [Int]
> divisors i = [j | j<-[1..i-1], i `rem` j == 0]
>
> perfect :: [Int]
> perfect = [i | i<-[1..10000], i == sum (divisors i)]
>
> main = print perfect
>
> % cat b.cpp
> #include <iostream>
> using namespace std;
>
> int main() {
>   for (int i = 1; i <= 10000; i++) {
>     int sum = 0;
>     for (int j = 1; j < i; j++)
>       if (i % j == 0)
>         sum += j;
>     if (sum == i)
>       cout << i << " ";
>   }
>   return 0;
> }
>
> %
>
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-- 

 Dusan Kolar            tel: +420 54 114 1238
 UIFS FIT VUT Brno      fax: +420 54 114 1270
 Bozetechova 2       e-mail: kolar at fit.vutbr.cz
 Brno 612 66
 Czech Republic

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