[Haskell-cafe] Global Arrays

[Lyndon Maydwell]

Could template-Haskell be used somehow?

- Lyndon Maydwell
On Mar 10, 2012 4:50 AM, "Clark Gaebel" <cgaebel at csclub.uwaterloo.ca> wrote:

> In Haskell, what's the canonical way of declaring a top-level array
> (Data.Vector of a huge list of doubles, in my case)? Performance is
> key in my case.
>
> The straightforward way would just be something like:
>
> globalArray :: V.Vector Double
> globalArray = V.fromList [ huge list of doubles ]
> {-# NOINLINE globalArray #-}
>
> However, I don't want to have to run the fromList at runtime. Not only
> would this mean a bigger executable (having to store a linked list,
> instead of an array), it would be quite inefficient since we don't
> even use the source list!
>
> Therefore, I was thinking of storing the array in a C file:
>
> static const double globalArray[] = { huge list of doubles };
> double* getGlobalArray() { return globalArray; }
> int        getGlobalArraySize() { return
> sizeof(globalArray)/sizeof(globalArray[0]); }
>
> And importing it in haskell witht he FFI, followed with an unsafeCast:
>
> foreign import ccall unsafe "getGlobalArray" c_globalArray :: Ptr CDouble
> foreign import ccall unsafe "getGlobalArraySize" c_globalArraySize :: CInt
>
> globalArray :: V.Vector Double
> globalArray = V.unsafeCast $ unsafeFromForeignPtr0 (unsafePerformIO $
> newForeignPtr_ c_globalArray) (fromIntegral c_globalArraySize)
> {-# NOINLINE globalArray #-}
>
> But this version (clearly) is full of "unsafe"ty. Is there a better
> way that I haven't thought of?
>
> Regards,
>  - clark
>
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