On 11/1/06, isto
Hi all,
On HaWiki was an announcement of MersenneTwister made by Lennart Augustsson. On a typical run to find out 10000000th rnd num the output is (code shown below):
$ time ./testMTla Testing Mersenne Twister. Result is [3063349438]
real 0m4.925s user 0m4.856s
I was exercising with the very same algorithm and tried to make it efficient (by using IOUArray): now a typical run looks like (code shown below):
$ time ./testMT Testing Mersenne Twister. 3063349438
real 0m3.032s user 0m3.004s
The original C-version (modified so that only the last number is shown) gives typically
$ time ./mt19937ar outputs of genrand_int32() 3063349438
real 0m0.624s user 0m0.616s
Results are similar with 64 bit IOUArray against 64 bit C variant. C seems to work about 5 to 10 times faster in this case.
I have tried to do different things but now I'm stuck. unsafeRead and unsafeWrite improved a bit the lazy (STUArray-version) and IOUArray-versions but not very much. I took a look of Core file but then, I'm not sure where the boxed values are ok. E.g. should IOUArray Int Word64 be replaced with something else?
Any hints and comments on how to improve the efficiency and make everything better will be appreciated a lot!
br, Isto
Greetings, Applying a few optimations can make it about 3x faster. 1. Hoist the array out of your loops. (See generateNumbers32, initialiseGenerator32 and genRNums). 2. Don't create too many new MT32 boxes. Most of the time is spent in 'next32' and changing its type to 'IOUArray Int Word32 -> Int -> IO (Word32, Int)' makes it much faster. 3. Demand more inlining. If you're using GHC, -funfolding-use-threshold=16 will substantially improve the performance. Using 'seq' is generally a bad idea. It can worsen the performance if not used carefully and GHCs strictness analyser is usually good enough. I used the profiler and -ddump-simpl to analyse this program. Donald suggested manual unboxing. However, in this case it won't help much (if at all) since GHC is doing such an excellent job on its own. -- Cheers, Lemmih