#1434: Slow conversion from Double to Int
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Reporter: [EMAIL PROTECTED] | Owner:
Type: bug | Status: new
Priority: normal | Milestone:
Component: libraries/base | Version: 6.4.1
Severity: normal | Resolution:
Keywords: | Difficulty: Unknown
Os: Linux | Testcase:
Architecture: Unknown |
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Comment (by [EMAIL PROTECTED]):
The following example is still certainly not the most compact one.
The above examples let me assume
that the difference between {{{round}}} and {{{double2Int}}}
is eliminated by the optimizer.
However, when I use {{{Int16}}} instead of {{{Int}}},
this optimization seems to fail, again.
{{{
{-# OPTIONS -O2 #-}
{- -package fps -package binary -}
module Main (main) where
import System.Time (getClockTime, diffClockTimes, tdSec, tdPicosec)
import System.Directory (removeFile)
import qualified Data.ByteString.Lazy as B
import qualified Data.Binary.Put as Bin
import Foreign (Int16)
import GHC.Float (double2Int)
type Sample = Int16 -- 'truncate' is slow
-- type Sample = Int -- 'truncate' is as fast as double2Int
writeSignalMonoBinaryPut ::
FilePath -> [Sample] -> IO ()
writeSignalMonoBinaryPut fileName =
B.writeFile fileName .
Bin.runPut .
mapM_ (Bin.putWord16host . fromIntegral)
numToSample :: Double -> Sample
numToSample x =
-- fromIntegral $ (truncate x :: Int)
truncate x
doubleToSample :: Double -> Sample
doubleToSample x =
fromIntegral $ double2Int x
{- * driver -}
measureTime :: String -> IO () -> IO ()
measureTime name act =
do putStr (name++": ")
timeA <- getClockTime
act
timeB <- getClockTime
let td = diffClockTimes timeB timeA
print (fromIntegral (tdSec td) +
fromInteger (tdPicosec td) * 1e-12 :: Double)
exponential2 :: Double -> Double -> [Double]
exponential2 k = iterate (k*)
sawSignalDouble :: Double -> [Double]
sawSignalDouble halfLife =
take 200000 (exponential2 halfLife 32767)
sawSignal16Trunc :: [Sample]
sawSignal16Trunc =
map numToSample (sawSignalDouble 0.999)
sawSignal16LowLevel :: [Sample]
sawSignal16LowLevel =
map doubleToSample (sawSignalDouble 0.999001)
tests :: [(String, FilePath, FilePath -> IO ())]
tests =
("saw double2Int", "saw-double2Int.sw", flip writeSignalMonoBinaryPut
sawSignal16LowLevel) :
("saw round", "saw-round.sw", flip writeSignalMonoBinaryPut
sawSignal16Trunc) :
[]
main :: IO ()
main =
do mapM (\(label, fileName, action) ->
measureTime label (action fileName))
tests
mapM_ (\(_,fileName,_) -> removeFile fileName)
tests
}}}
For {{{type Sample = Int16}}} I get
{{{
$ ghc-6.6.1 -package binary RoundTest.hs && a.out
saw double2Int: 8.7173e-2
saw round: 0.430843
}}}
For {{{type Sample = Int}}} I get
{{{
$ ghc-6.6.1 -package binary RoundTest.hs && a.out
saw double2Int: 8.8279e-2
saw round: 9.8028e-2
}}}
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/1434>
GHC <http://www.haskell.org/ghc/>
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