Re: major missing piece to arrays?

[Jérémy Bobbio]

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On 15 juil. 04, at 13:26, John Meacham wrote:
Perhaps I am just missing something, but a major piece of efficient
array functionality seems to be missing. Namely the ability to
efficiently copy spans of arrays into one another and/or compare spans
of memory. (basically memcpy and memcmp from C).
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
It seems to work on GHC 6.2.1, though I did not made further tests than 
this main.

Hope this helps,
Jérémy.
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