I couldn't find a functionality like 'round to fraction', which would try round a floating point value to its nearby fraction portion:
round2fraction(1.4, 0.5); -> 1.5 round2fraction(1.8, 0.5); -> 2.0 round2fraction(1.0, 0.5); -> 1.0 round2fraction(1.25, 0.5); -> 1.5 round2fraction(-1.6, 0.5); -> -1.5
We have here a private implementation, but this is probably not as optimised as those numerical guru's can come up with. Is this a good suggestion to add to Boost.Math or overkill?
Probably overkill to add to Boost.Math, but how about: template <class T> T round2fraction(T x, T f) { return f * round(x/f); } where "round" is either the C99 one or the boost::math:: one if you need something more generic. Of course this assumes that parameter "f" is exactly representable as a floating point value, in fact it might need to be a power of 2 in order to be certain of being completely safe and accurate.... HTH, John.