Eric Willigers wrote:
Do the two programs implement the same algorithm? The C program updates x and y in sequence. The Haskell program updates x and y in parallel and can be easier for the compiler to optimize.
Hi Don, Expressing this in other words, do we want the new y to be based on the new x or on the old x? I extracted the code you posted to CS.c and HP.hs (C sequential, Hashell parallel). I made the following minor changes to form CP.c and HS.hs (C parallel, Hashell sequential):- double xn; for (; i<=1000000000; i++) { xn = x*y/3.0; y = x*9.0; x = xn; } | otherwise = go xs (xs*9) (i+1) where xs = x*y/3 Tested on a 2.8 GHz Pentium 4, running XP SP2 and cygwin, using the compiler options from your post. Each program was run once. $ uname -a CYGWIN_NT-5.1 nemo 1.5.21(0.156/4/2) 2006-07-30 14:21 i686 Cygwin $ gcc --version gcc (GCC) 3.4.4 (cygming special) (gdc 0.12, using dmd 0.125) $ ghc --version The Glorious Glasgow Haskell Compilation System, version 6.6 $ gcc -O3 -ffast-math -mfpmath=sse -msse2 -std=c99 CP.c -o CP $ time ./CP 3.333333 real 0m10.560s user 0m10.546s sys 0m0.015s $ gcc -O3 -ffast-math -mfpmath=sse -msse2 -std=c99 CS.c -o CS $ time ./CS 3.333333 real 0m10.788s user 0m10.718s sys 0m0.015s $ ghc -O -fexcess-precision -fbang-patterns -optc-O3 -optc-ffast-math -optc-mfpmath=sse -optc-msse2 HP.hs -o HP $ time ./HP 3.3333333333333335 real 1m8.550s user 0m0.015s sys 0m0.031s $ ghc -O -fexcess-precision -fbang-patterns -optc-O3 -optc-ffast-math -optc-mfpmath=sse -optc-msse2 HS.hs -o HS $ time ./HS 3.3333333333333335 real 1m9.425s user 0m0.015s sys 0m0.046s The differences between the P and S versions turned out to be incidental on my system. I downloaded GHC a month ago. Should I be running a more recent build or using different compiler options? Regards, Eric.