[Haskell-cafe] fast image processing in haskell?

[Jeff Briggs]

On 05/08/06, Chris Kuklewicz <haskell at list.mightyreason.com> wrote:
> I suggest trying something, using "/usr/bin/ghc -O3 -optc-O3" like this:
>
> > {-# OPTIONS_GHC -funbox-strict-fields #-}
> >
> > import Foreign
> > import Control.Monad
> >
> > data Cam = Cam { snap_width   :: !Int
> >                , snap_height  :: !Int
> >                , snap_bytespp :: !Int
> >                , snap_size    :: !Int
> >                , cam_img      :: Ptr Word8
> >                , cam_obj      :: ForeignPtr ()
> >                }
> >
> >
> > type F = Word8 -> Word8 -> Word8 -> Int -> Int -> Int
> >
> > {-# INLINE cam_snap_3 #-}
> > cam_snap_3 :: Cam -> F -> Int -> IO Int
> > cam_snap_3 cam f x =
> >   let end = snap_size cam
> >       loop ptr n x | ptr `seq` n `seq` x `seq` False = undefined
> >                    | n >= end = return x
> >                    | otherwise = do
> >         r <- peek ptr
> >         g <- peek (advancePtr ptr 1)
> >         b <- peek (advancePtr ptr 2)
> >         loop (advancePtr ptr 3) (n+3) (f r g b n x)
> >   in loop (cam_img cam) 0 x
>

Ah, so excessive laziness and IO were killing it! Thanks! This works
most excellently :)