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style="font-family: -moz-fixed; font-size: 13px;" lang="x-western">Hello
again folks,
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<br>
Sorry to keep troubling you - I'm very appreciative of the help you've
given so far. I've got one more for you that has got me totally
stumped. I'm writing a program which deals with largish-files, the one
I am using as a test case is not stupidly large at about 200mb. After
three evenings, I have finally gotten rid of all the stack overflows,
but I am unfortunately left with something that is rather unfeasably
slow. I was hoping someone with some keener skills than I could take a
look, I've tried to distill it to the simplest case.
<br>
<br>
This program just reads in a file, interpreting each value as a double,
and does a sort of running average on them. The actual function doesn't
matter too much, I think it is the reading it in that is the problem.
Here's the code:
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<br>
import Control.Exception
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import qualified Data.ByteString.Lazy as BL
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import Data.Binary.Get
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import System.IO
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import Data.Binary.IEEE754
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myGetter acc = do
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e <- isEmpty
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if e == True
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then
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return acc
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else do
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t <- getFloat64le
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myGetter $! ((t+acc)/2)
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myReader file = do
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h <- openBinaryFile file ReadMode
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bs <- BL.hGetContents h
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return $ runGet (myGetter 0) bs
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main = do
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d <- myReader "data.bin"
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evaluate d
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<br>
This takes about three minutes to run on my (fairly modern) laptop..
The equivilant C program takes about 5 seconds.
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<br>
I'm sure I am doing something daft, but I can't for the life of me see
what. Any hints about how to get the profiler to show me useful stuff
would be much appreciated!
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<br>
All the best,
<br>
<br>
Philip
<br>
<br>
PS: If, instead of computing a single value I try and build a list of
the values, the program ends up using over 2gb of memory to read a
200mb file.. any ideas on that one?
<br>
<br>
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