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.
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