On Thu, Nov 29, 2012 at 1:32 PM, Daniel Fischer <daniel.is.fisc...@googlemail.com> wrote: > We have an unpleasant regression in comparison to 7.2.* and the 7.4.* were > slower than 7.6.1 is, but it's all okay here (not that it wouldn't be nice to > have it faster still). > > Are you on a 32-bit system?
This version works around the Word->Double conversion bug and shows good performance: (Always compile with -Wall, it tells you if some arguments are defaulted to slow Integers, instead of fast Ints.) {-# LANGUAGE CPP, BangPatterns, MagicHash #-} module Main (main) where #define VDIM 100 #define VNUM 100000 import Control.Monad.ST import Data.Array.Base import Data.Array.ST import Data.Bits import GHC.Word import GHC.Exts prng :: Word -> Word prng w = w' where w1 = w `xor` (w `shiftL` 13) w2 = w1 `xor` (w1 `shiftR` 7) w' = w2 `xor` (w2 `shiftL` 17) type Vec s = STUArray s Int Double kahan :: Vec s -> Vec s -> ST s () kahan s c = do let inner !w j | j < VDIM = do cj <- unsafeRead c j sj <- unsafeRead s j let y = word2Double w - cj t = sj + y w' = prng w unsafeWrite c j ((t-sj)-y) unsafeWrite s j t inner w' (j+1) | otherwise = return () outer i | i < VNUM = inner (fromIntegral i) 0 >> outer (i + 1) | otherwise = return () outer (0 :: Int) calc :: ST s (Vec s) calc = do s <- newArray (0,VDIM-1) 0 c <- newArray (0,VDIM-1) 0 kahan s c return s main :: IO () main = print . elems $ runSTUArray calc word2Double :: Word -> Double word2Double (W# w) = D# (int2Double# (word2Int# w)) On my (64-bit) machine the Haskell and C versions are on par. -- Johan _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe