Where is the `unsafeAt` function? I can't seem to find it ( http://haskell.org/hoogle/?hoogle=unsafeat).
For reference I have asked the same question on StackOverflow. One person suggested that the reason might be that Int64 on Windows is broken ( http://stackoverflow.com/questions/6970904/analyzing-slow-performance-of-a-haskell-program/6976448#6976448 ). I tried the same test on Arch Linux x64 (GHC 7.0.3) but it still can't complete in 3 minutes, where as a new C++ version I wrote completes in 45 seconds (because I didn't want to use Mono for benchmarks. For reference here is the C++ implementation http://ideone.com/vZGhh (Again, ironically shorter than Haskell and actually looks quite clean)) The profile under x64 Linux is similar to the one posted before -- most allocations and time spent in wordLength'. It seems mysterious that such an innocent program is so obscure to write "correctly" in Haskell :P Chris On Mon, Aug 8, 2011 at 1:40 AM, Eugene Kirpichov <ekirpic...@gmail.com>wrote: > What about using unsafe array indexing operations? (i.e. array `unsafeAt` > index) > > 2011/8/7 Chris Yuen <kizzx2+hask...@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.fisc...@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@haskell.org > > http://www.haskell.org/mailman/listinfo/haskell-cafe > > > > > > > > -- > Eugene Kirpichov > Principal Engineer, Mirantis Inc. http://www.mirantis.com/ > Editor, http://fprog.ru/ >
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