Of course I know that the list version is very unfair, but I wanted to see
what was the trade off between elegance and speed.
Regarding whether low level programming makes sense or not, I was just
curious to see what are the limits of Haskell. Moreover there is not much
literature on high performance Haskell programming (tricks like
unsafeWrite), at least organized in a systematic and concise way.
My original problem was writing a fast library for simple matrix
computations (i.e. multiplication and inversion for small dense matrices).
I have not been able to make GSLHaskell work with Lapack so far. :(
Anyway here are the new versions and timings, I increased the number of
times the vector is reversed, I also compiled everything with -O2.
time ./arrayC
499
real 0m0.244s
user 0m0.236s
sys 0m0.005s
time ./list
499
real 0m11.036s
user 0m10.770s
sys 0m0.118s
time ./IOMutArrayUnboxed
499
real 0m2.573s
user 0m2.408s
sys 0m0.042s
time ./IOMutUnbUnsafe
499
real 0m2.264s
user 0m2.183s
sys 0m0.025s
------------------------------
--------------------------------------------------
//compile with g++ -O2 -o arrayC arrayC.cc
#include < stdio.h>
#include <math.h>
int main()
{
int array[500001];
for (int i=0;i<=500000;i++)
{
array[i]=(19*i+23)%911;
}
int tmp=0;
for (int cnt=0;cnt<120;cnt++)
{
for (int x=0;x<=250000;x++)
{
tmp=array[500000-x];
array[500000-x]=array[x];
array[x]=tmp;
}
}
int result=0;
for (int i=0;i<=500000;i++)
{
result=result+(array[i]%911);
}
result=result % 911;
printf("%d",result);
return 0;
}
--------------------------------------------------------------------------------
-- compile with
-- ghc -O2 --make -o list list.hs
module Main
where
import Data.List
testArray = [ (19*i+23) `mod` 911 |i <- [0..500000]]
sumArrayMod = foldl (\x y -> (y+x) `mod` 911) 0
main = print $ sumArrayMod$
foldl (.) id (replicate 120 reverse) $testArray
--------------------------------------------------------------------------------------
-- compile with
-- ghc -O2 --make -o IOMutArrayUnboxed IOMutArrayUnboxed.hs
module Main
where
import Monad
import Data.Array.IO <http://data.array.io/>
import Data.Array.MArray
import Data.Array.Unboxed
total, semiTotal ::Int
total= 500000 <javascript:void(0)>
semiTotal=250000
testArray :: IO (IOUArray Int Int)
testArray = newListArray (0,total) [(19*i+23) `mod` 911 |i <- [0..total]]
reverseArray :: IOUArray Int Int -> IO ()
reverseArray arr = mapM_ (\i -> do oldi <- readArray arr i
oldj <- readArray arr (total-i)
writeArray arr i oldj
writeArray arr (total-i) oldi)
[0..semiTotal]
sumArrayMod :: IOUArray Int Int -> IO Int
sumArrayMod arr = foldM (\s i -> do x <- readArray arr i
return $!(s+x) `mod` 911) 0 [0..total]
main::IO()
main = testArray >>= \a ->
sequence (replicate 120 $reverseArray a)>>
sumArrayMod a >>= print
------------------------------------------------------------------------------------
-- compile with
-- ghc -O2 --make -o IOMutUnbUnsafe IOMutUnbUnsafe.hs
module Main
where
import Monad
import Data.Array.IO <http://data.array.io/>
import Data.Array.MArray
import Data.Array.Unboxed
import Data.Array.Base ( unsafeWrite, unsafeRead )
total, semiTotal ::Int
total= 500000 <javascript:void(0)>
semiTotal=250000
testArray :: IO (IOUArray Int Int)
testArray = newListArray (0,total) [(19*i+23) `mod` 911 |i <- [0..total]]
reverseArray :: IOUArray Int Int -> IO ()
reverseArray arr = mapM_ (\i -> do oldi <- unsafeRead arr i
oldj <- unsafeRead arr (total-i)
unsafeWrite arr i oldj
unsafeWrite arr (total-i) oldi)
[0..semiTotal]
sumArrayMod :: IOUArray Int Int -> IO Int
sumArrayMod arr = foldM (\s i -> do x <- unsafeRead arr i
return $!(s+x) `mod` 911) 0 [0..total]
main::IO()
main = testArray >>= \a ->
doFromTo 1 120 (\_ -> reverseArray a) >> sumArrayMod a >>= print
{-# INLINE doFromTo #-}
-- do the action for [from..to], ie it's inclusive.
doFromTo :: Int -> Int -> (Int -> IO ()) -> IO ()
doFromTo from to action =
let loop n | n > to = return ()
| otherwise = do action n
loop (n+1)
in loop from
-----------------------------------------------------------------------
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