[Haskell-cafe] Analyzing slow performance of a Haskell program

[Eugene Kirpichov]

What about using unsafe array indexing operations? (i.e. array `unsafeAt` index)

2011/8/7 Chris Yuen <kizzx2+haskell at gmail.com>:
> Here is an updated version using Data.Array.Unboxed  http://ideone.com/YXuVL
> And the profile http://hpaste.org/49940
>
> Still taking 5+ minutes...
>
> Chris
>
> On Sun, Aug 7, 2011 at 5:20 PM, Daniel Fischer
> <daniel.is.fischer at googlemail.com> wrote:
>>
>> On Sunday 07 August 2011, 10:52:20, Max Bolingbroke wrote:
>> > In short I don't see how to get further without changing the algorithm
>> > or doing some hacks like manual unrolling. Maybe someone else has some
>> > ideas?
>>
>> Well, the C# implementation uses arrays for lookup while the Haskell
>> version uses list lookups
>>
>>                      in (tens !! fromIntegral t) ++ wordify x
>>
>> and case'd functions
>>
>> lenTens 0 = 0
>> lenTens 1 = 3
>> lenTens 2 = 6
>> lenTens 3 = 6
>> lenTens 4 = 5
>> lenTens 5 = 5
>> lenTens 6 = 5
>> lenTens 7 = 7
>> lenTens 8 = 6
>> lenTens 9 = 6
>>
>> wordify is only called once at the end, so that should not have a
>> measurable impact, but the lenXXXs might.
>> I'm not sure what
>>
>> CaseLen.$wlenTens :: GHC.Prim.Int# -> GHC.Prim.Int#
>> [GblId,
>>  Arity=1,
>>  Str=DmdType L,
>>  Unf=Unf{Src=<vanilla>, TopLvl=True, Arity=1, Value=True,
>>         ConLike=True, Cheap=True, Expandable=True,
>>         Guidance=IF_ARGS [12] 11 0}]
>> CaseLen.$wlenTens =
>>  \ (ww_shY :: GHC.Prim.Int#) ->
>>    case ww_shY of _ {
>>      __DEFAULT ->
>>        CaseLen.lenTens1
>>        `cast` (CoUnsafe GHC.Types.Int GHC.Prim.Int#
>>                :: GHC.Types.Int ~ GHC.Prim.Int#);
>>      0 -> 0;
>>      1 -> 3;
>>      2 -> 6;
>>      3 -> 6;
>>      4 -> 5;
>>      5 -> 5;
>>      6 -> 5;
>>      7 -> 7;
>>      8 -> 6;
>>      9 -> 6
>>    }
>>
>> means at a lower level, but it's certainly worth trying out whether an
>> unboxed array lookup is faster.
>
>
> _______________________________________________
> Haskell-Cafe mailing list
> Haskell-Cafe at haskell.org
> http://www.haskell.org/mailman/listinfo/haskell-cafe
>
>



-- 
Eugene Kirpichov
Principal Engineer, Mirantis Inc. http://www.mirantis.com/
Editor, http://fprog.ru/