Re: [Haskell-cafe] Big Arrays

On Sun, Oct 3, 2010 at 19:09, Bryan O'Sullivan wrote:

On Sun, Oct 3, 2010 at 11:54 AM, Henry Laxen wrote:

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I am trying to create a (relatively) big array, but it seems I cannot make anything larger than 2^30 or so.  Here is the code:

Use a 64-bit machine, where Int is 64 bits wide. Trying to create a larger array on a 32-bit machine doesn't make any sense.

Sure it does; a 32-bit system can address much more than 2**30 elements. Artificially limiting how much memory can be allocated by depending on a poorly-specced type like 'Int' is a poor design decision in Haskell and GHC. OP: for this particular use case (unboxed Word64), an easily solution is to have some structure like (data BigArray a = BigArray (UArray Word32 a) ((UArray Word32 a) ((UArray Word32 a) ((UArray Word32 a)), with each array containing 2^30 elements. You'll need to write custom indexing and modification functions, to process the index and pass it to the appropriate array. Something like: idxBig :: BigArray a -> Word32 -> (UArray Word32 a, Word32) idxBig (BigArray a0 a1 a2 a3) i | i < 2^30 = (a0, i) | i < 2^31 = (a1, i - 2^30) | i < 2^30 + 2^31 = (a2, i - 2^31) | i < 2^32 = (a3, i - 2^31 - 2^30) Then wrap the existing array functions: idx :: BigArray a -> Word32 -> a idx arr i = let (arr', i') = idxBig arr i in arr' ! i'