Could template-Haskell be used somehow?
- Lyndon Maydwell
On Mar 10, 2012 4:50 AM, "Clark Gaebel"
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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