properFraction implemented with modf primitive?
I need a fast 'fraction' function for Double. I can use 'properFraction', but its Double instance uses 'decodeFloat', which is rather slow. It's also clumsy to use, because I have to provide an Integral type, although I'm not interested in the integral part. I can use (x - int2Double (double2Int x)) but this fails for x beyond the Int number range, and it is hard to fix that for an unknown implementation of Double.
What about a 'modf' primitive which either calls 'modf' from standard C library or invokes an appropriate FPU command? If Double is in IEEE format the 'fraction' command could also be implemented quite efficiently by some bit masking without the FPU.