
Hello, I just rewrote my levmar library[1] to use Vectors (from the vector package[2]) instead of lists. I was expecting to see a significant performance improvement. Unfortunately I only saw a 10% improvement. However, I noticed I had a lot of conversions from Vector Double to Vector CDouble and visa versa in my code: import Data.Vector.Storable ( Vector ) mapRealToFrac ∷ (Storable α, Storable β, Real α, Fractional β) ⇒ Vector α → Vector β mapRealToFrac = VS.map realToFrac When I replace this with: mapRealToFrac = unsafeCoerce My application computes the same result but does it 28 times faster! My question are: 1) Is this always safe? In other words: are the runtime representations of Double and CDouble always equivalent or do they vary between platforms? 2) Can the same improvement be accomplished using RULE pragma's? 3) Are there disadvantages of using CDouble instead of Double in the levmar API? For some reason it feels wrong to use CDouble in the API but I don't have a good argument against it yet. Thanks, Bas [1] http://hackage.haskell.org/package/levmar [2] http://hackage.haskell.org/package/vector