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/Dat... 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...)