major missing piece to arrays?

[Shawn Garbett]

--- Jérémy_Bobbio <jbobbio at insia.org> 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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