On Thu, 21 Jun 2007 11:55:04 +0100 Philip Armstrong <[EMAIL PROTECTED]> wrote:
> In odd spare moments, I took John Harrops simple ray tracer[1] & made > a Haskell version: > > http://www.kantaka.co.uk/cgi-bin/darcsweb.cgi?r=ray > > darcs get http://www.kantaka.co.uk/darcs/ray > > It's pretty much a straight translation into idiomatic Haskell (as far > as my Haskell is idiomatic anyway). > > Unfortunately, it's a lot slower than the ML version, despite turning > all the optimisation options up as far as they'll go. Profiling > suggests that much of the time is spent in the intersection' function, > and that the code is creating (and garbage collecting) an awful lot of > (-|) vector subtraction thunks. Trying to make intersection' or > ray_sphere stricter (with seq) appears to have no effect whatsoever: > the output of -ddump-simpl is unchanged (with the arguments all > staying lazy). > > Am I missing anything obvious? I don't want to carry out herculean > code rewriting efforts: that wouldn't really be in the spirit of the > thing. > > cheers, Phil > > [1] http://www.ffconsultancy.com/languages/ray_tracer/comparison.html > With a very minor change (attached), your Haskell ray tracer runs faster than the OCaml version on my machine. There's a bug GHC where it does not recognize -fexcess-precision at the command line, but an OPTIONS_GHC pragma does work correctly. This flag brings runtime from about 60s to 20s on my machine (Core Duo 1.83GHz) -- compared to 25s for the OCaml version. Results (each run twice to avoid OS buffering of the executable): % uname -a Linux localhost 2.6.22-rc4 #5 SMP Tue Jun 19 17:29:36 CDT 2007 i686 Genuine Intel(R) CPU T2400 @ 1.83GHz GenuineIntel GNU/Linux % ghc --version The Glorious Glasgow Haskell Compilation System, version 6.6 % ocamlopt -version 3.09.3 % (time ./hsray) | md5sum ./hsray 20.23s user 0.03s system 98% cpu 20.536 total 63a359e5c388f2004726d83d4337f56b - % (time ./hsray) | md5sum ./hsray 19.74s user 0.07s system 99% cpu 19.907 total 63a359e5c388f2004726d83d4337f56b - % (time ./mlray) | md5sum ./mlray 25.55s user 0.00s system 98% cpu 25.831 total 63a359e5c388f2004726d83d4337f56b - % (time ./mlray) | md5sum ./mlray 25.63s user 0.04s system 98% cpu 25.981 total 63a359e5c388f2004726d83d4337f56b - Cheers, Spencer Janssen
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