Hi Folks,

I had to transform Packed Decimal file into csv format (does anybody here know
what this Mainframe format is?).  Because of the file size I could not do
this on mainframe directly. So I've created simply program using ByteString.
Generally I'm happy with my solution: pgm processes arroud 2MB/s on my pc, so
my 3GB file was transformed in reasonable 30 min time.

My question is: how to do this faster?

{code}
module Main
where

import qualified Data.ByteString.Lazy as B

main =  B.getContents >>= myPrint . myConcat . B.unpack

myConcat = myConcat' 0

myConcat' :: (Integral a) => Integer -> [a] -> [Integer]
myConcat'  _  [] = []
myConcat' acc (x:xs) = case x `mod` 16 of
               12 -> (10*acc + (restOf . fromIntegral) x) : myConcat' 0 xs
               13 -> ((-10)*acc + (restOf . fromIntegral) x) : myConcat' 0 xs
               15 -> (10*acc + (restOf . fromIntegral) x) : myConcat' 0 xs
               10 -> fail $ show acc
               11 -> fail $ show acc
               14 -> fail $ show acc
                v  -> myConcat' (100*acc + (numberOf . fromIntegral) x) xs
        where restOf n = (n - 12) `div` 16
              numberOf n = n - 6 * (n `div` 16)

myPrint [] = return ()
myPrint xs = mapM_ myShow (take 14 xs) >> putStrLn "" >> myPrint (drop 14 xs)

myShow x = (putStr . show) x >> putStr ";"
{code}

I knew that csv output had to be 14 fields per line.

Best,
Bartek


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