[Haskell-cafe] Re: New slogan for haskell.org

Laurent Deniau laurent.deniau at cern.ch
Thu Nov 29 08:17:07 EST 2007

Mirko Rahn wrote:
>> The following code is the direct translation of your Haskell code
>> void f(int x, intset s) {
>>   printf("%d, ", x);
>>   f (intset_elem(s, x/2) ? 3*x : x/2, intset_put(s, x));
>> }
> No, not that easy. The Haskell code works with arbitrary precision 
> Integer, the C code with a fixed size int. On a 32 bit machine, try to 
> calculate a_{1805133}, which equals to 19591041024. Or a_{8392780} = 
> 26665583616. Or a_{8500000} = 10804333. These values are calculated with 
> the Haskell program in 370s and ~1GB memory usage.

This is also a work for a library (BTW like Haskell does), you can use 
gmp or mpfr. This will just add one line to store x/2 in y and avoid its 
recomputation. You will also have to switch from intset to set. And 
there one can start to see the difference. The code refactoring will be 
longer since C doesn't support parametric polymorphism nor operator 

> Fair enough, on the same machine a C program (*two* pages long) was able 
> to calculate a_{23448481} = 594261577728 and a_{25000000} = 192365946 in 
> 50s and ~1GB memory usage.


a+, ld.

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