double rounding in xtime_diff()?

[Antoine Leca]

Markus Kuhn wrote:
> 
> A somewhat related question: Given a floating-point value X,
> is there in C9X a portable way to get the next smaller and the
> next larger floating point value?

Yes.  Seek for nextafter() or nextafterx() in C9X draft.


7.12.11.3  The nextafter functions

Synopsis

        #include <math.h>
        double nextafter(double x, double y);
        float nextafterf(float x, float y);
        long double nextafterl(long double x, long double y);

Description

[#2]    The   nextafter   functions   determine   the   next
representable value, in the type of the function, after x in
the direction of y, where x and y are first converted to the
type of the function.



Antoine