Re: [Haskell-cafe] Performance question

Do you think it would be feasable to replace the GHC implementation of System.Random with something like System.Random.Mersenne?

Here is a variant that uses mersenne-random-pure64 and works less than 2x slower than C++:

- You don't need to compute samples count an extra time - You don't need to assemble double pairs from a list - Notice the strictness in randomDoublePairs: it doubled performance

{-# LANGUAGE BangPatterns #-}

import System.Random.Mersenne.Pure64 import System( getArgs ) import Data.List( foldl' )

isInCircle :: (Double,Double) -> Bool isInCircle (!x,!y) = sqrt (x*x + y*y) <= 1.0

accumulateHit :: Int -> (Double,Double) -> Int accumulateHit !hits pair = if isInCircle pair then hits + 1 else hits

monteCarloPi :: Int -> [(Double,Double)] -> Double monteCarloPi n xs = 4.0 * fromIntegral hits / fromIntegral n where hits = foldl' accumulateHit 0 . take n $ xs

randomDoublePairs g = let !(!x,!g') = randomDouble g !(!y,!g'') = randomDouble g' in (x,y):randomDoublePairs g''

main = do samples <- (read . head) `fmap` getArgs randomNumbers <- randomDoublePairs `fmap` newPureMT putStrLn . show $ monteCarloPi samples randomNumbers

jkff@*****:~/montecarlo$ time ./mc-hs 10000000 3.1417088

real 0m1.141s user 0m1.140s sys 0m0.000s jkff@*****:~/montecarlo$ time ./mc 10000000 10000000 3.14113

real 0m0.693s user 0m0.690s sys 0m0.000s

2009/2/26 Ben Lippmeier :

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On 26/02/2009, at 9:27 PM, haskell@kudling.de wrote:

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Currently i can only imagine to define a data type in order to use unboxed Ints instead of the accumulator tuple.

That would probably help a lot. It would also help to use two separate Double# parameters instead of the tuple.

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The thing is that i don't see in the profile output yet what to improve. There are some allocations going on in "main", but i don't know what causes it.

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The first thing I would do is replace your isInCircle :: (Floating a, Ord a)  => (a,a) -> Bool with isInCircle :: (Double, Double) -> Bool

Can you point me to why that matters?

At the machine level, GHC treats the (Floating a, Ord a) as an extra argument to the function. This argument holds function pointers that tell

it

...

how to perform multiplication and <= for the unknown type 'a'. If you use Double instead of 'a', then it's more likely to use the actual machine op.

Ben.

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