Re: [Haskell-cafe] Fast number parsing with strict bytestrings [Was: Re: Seemingly subtle change causes large performance variation]

dons:

mdanish:

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Hello,

I've been playing with the INTEST problem on SPOJ which demonstrates the ability to write a program which processes large quantities of input data. http://www.spoj.pl/problems/INTEST/

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But when I make a slight modification, the program chews up a ton more memory and takes more time:

import Control.Monad import Data.Maybe import qualified Data.ByteString.Char8 as B

divisibleBy :: Int -> Int -> Bool a `divisibleBy` n = a `rem` n == 0

main :: IO () main = do [n,k] <- (map int . B.split ' ') `fmap` B.getLine :: IO [Int]

let doLine :: Int -> Int -> IO Int doLine r _ = B.getLine >>= return . testDiv r -- 'return' moved here ^^

And just following up with some GC statistics: Original, 95% cpu 1.668 total <> Too lazy: 96% cpu 4.219 total < 14729345/52642396 avg/max bytes residency (7 samples), --> 85M in use, 0.00 INIT (0.00 elapsed), 1.68 MUT (1.81 elapsed), --> 2.07 GC (2.36 elapsed) :ghc>> (clear space leak) Fixing above program with $!: 94% cpu 1.656 total < 2288/2288 avg/max bytes residency (1 samples), --> 1M in use, 0.00 INIT (0.00 elapsed), 1.49 MUT (1.64 elapsed), 0.01 GC (0.01 elapsed) :ghc>> Using lazy bytestrings for pure processing: 90% cpu 1.424 total <> And the killer strict chunk parser: 78% cpu 0.327 total < 38 GCs, --> 81348/81348 avg/max bytes residency (1 samples), 2M in use, 0.00 INIT (0.00 elapsed), --> 0.21 MUT (0.32 elapsed), 0.00 GC (0.00 elapsed) :ghc>> Very little data shuffled around in the last one. -- Don