Re: major missing piece to arrays?

15 Jul 2004

      --- J�r�my_Bobbio  wrote:
...
memcpy is available in Foreign.Marshal.Utils:
copyBytes :: Ptr a -> Ptr a -> Int -> IO ()
Copies the given number of bytes from the
second area (source)
     into the first (destination);the copied areas
may not overlap
Here is the result of a quick try to implement fast
copy using it and 
Data.Array.Storable:
module FastArrrayCopy where
import Data.Array.Storable
import Foreign.Ptr
import Foreign.Storable
import Foreign.Marshal.Utils ( copyBytes )
fastArrayCopy :: (Storable e1, Ix i, Ix i1)
           => StorableArray i1 e1 -> i1
           -> StorableArray i e -> i -> Int -> IO ()
fastArrayCopy src srcStart dest destStart count
     | destOffset + count > rangeSize (bounds dest)
= error "Out of 
bounds"
     | otherwise =
         withStorableArray src $ \ pSrc ->
             withStorableArray dest $ \ pDest ->
                 do dummy <- peek pSrc
                    copyBytes (pDest `plusPtr`
(destOffset * sizeOf 
dummy))
                              (pSrc `plusPtr`
(srcOffset * sizeOf dummy))
                              (count * sizeOf dummy)
     where srcOffset = index (bounds src) srcStart
           destOffset = index (bounds dest)
destStart
main :: IO ()
main =
     do a <- newListArray (0, 100) ([0..] :: [Int])
        a' <- newArray (0, 50) (42 :: Int)
        getElems a' >>= print
        copyRange a 10 a' 15 20
        getElems a' >>= print
This should be in a FAQ somewhere for those of us
damaged by years of coding in C.

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Re: major missing piece to arrays?

Shawn Garbett