On 19/05/2011, at 8:27 PM, Christian Höner zu Siederdissen wrote:
> I'd like to use repa in a rather perverted mode, I guess:
>
> for my programs I need to be able to update arrays in place and
> repeatedly perform operations on them.
> Right now, it basically works like this (in ST):
>
> - create unboxed space using "primitive" (same as unboxed vectors)
> - unsafefreeze unboxed space
> - perform calculations on frozen, immutable space
> - write result into mutable space (which is shared with the unsafefrozen
> space)
If you care deeply about inplace update, then you could use the parallel array
filling functions directly. The ones in D.A.Repa.Internals.Eval*.hs. For 2D
images, use the fillVectorBlockwiseP [1] or fillCursoredBlock2P.
fillVectorBlockwiseP
:: Elt a
=> IOVector a -- ^ vector to write elements into
-> (Int -> a) -- ^ fn to evaluate an element at the given
index
-> Int -- ^ width of image.
-> IO ()
-- | Fill a block in a 2D image, in parallel.
-- Coordinates given are of the filled edges of the block.
-- We divide the block into columns, and give one column to each thread.
fillCursoredBlock2P
:: Elt a
=> IOVector a -- ^ vector to write elements into
-> (DIM2 -> cursor) -- ^ make a cursor to a particular
element
-> (DIM2 -> cursor -> cursor) -- ^ shift the cursor by an offset
-> (cursor -> a) -- ^ fn to evaluate an element at the
given index.
-> Int -- ^ width of whole image
-> Int -- ^ x0 lower left corner of block to fill
-> Int -- ^ y0 (low x and y value)
-> Int -- ^ x1 upper right corner of block to fill
-> Int -- ^ y1 (high x and y value, index of last elem
to fill)
-> IO ()
Actually, it might be worthwhile exporting these in the API anyway.
[1]
http://code.ouroborus.net/repa/repa-head/repa/Data/Array/Repa/Internals/EvalBlockwise.hs
[2]
http://code.ouroborus.net/repa/repa-head/repa/Data/Array/Repa/Internals/EvalCursored.hs
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