[Haskell-cafe] floating point operations and representation

[David Roundy]

On Wed, Mar 12, 2008 at 9:27 PM, Don Stewart <dons at galois.com> wrote:
>  You could consider binding directly to the C functions, if needed,
>
>     {-# OPTIONS -fffi -#include "math.h" #-}
>
>     import Foreign.C.Types
>
>     foreign import ccall unsafe "math.h log10"
>         c_log10 :: CDouble -> CDouble
>
>     log10 :: Double -> Double
>     log10 x = realToFrac (c_log10 (realToFrac x))

Actually, you could almost certainly just use

foreign import ccall unsafe "math.h log10" log10 :: Double -> Double

since in ghc CDouble and Double are identical.

It's a bit sloppier, but shouldn't cause any trouble.  And I've no
idea how realToFrac is implemented, but would worry about it behaving
oddly... for instance when given NaNs.

David