Vo Minh Thu wrote:
Hi,
I would like to benchmark C/C++ and Haskell code. The goal is to
improve the Haskell port[0] of smallpt[1].
To make sure my approach was reliable, I got the code of two programs
(one in C, the other in Haskell) from a post[2] by Don. The code is
reproduced below. When timing the execution of both program, I have a
4x difference. It is said on the blog the programs should have
similar performance.
I simply don't get the reason of such a difference. I've tried the
code on my Atom netbook and also on an older centrino machine. The
timing are similar (i.e. the C and Haskell program show >4x
difference). Both machines have GHC 6.12.1 on Linux.
Would you have an idea?
The function floor :: Double -> Int is surprisingly slow under GHC.
(IIRC, it's implemented by converting Double -> (Int, Integer) -> Int,
or something equally absurd.) Poking around GHC.Prim directly allows you
to do the same operation much, much faster. I couldn't say exactly how
much of a difference it makes, but I've had programs go from seconds to
microseconds just by switching this.
http://hackage.haskell.org/trac/ghc/ticket/2271
http://hackage.haskell.org/trac/ghc/ticket/1434
My solution was to do this:
http://hackage.haskell.org/packages/archive/AC-Colour/1.1.3/doc/html/src/Data-Colour-FastFloor.html
Uh... good luck! o_O
(Of course, I could be speaking complete nonesense and this bug has
since been fixed, or the cause of the slowness in smallpt is something
else...)
_______________________________________________
Haskell-Cafe mailing list
[email protected]
http://www.haskell.org/mailman/listinfo/haskell-cafe
