nextafterf(3) -- Linux man page
NAMEnextafter, nextafterf, nextafterl, nexttoward, nexttowardf, nexttowardl - floating point number manipulation
double nextafter(double x, double y);
float nextafterf(float x, float y);
long double nextafterl(long double x, long double y);
DESCRIPTIONThe nextafter() functions return the next representable neighbor of x in the direction towards y. The size of the step between x and the result depends on the type of the result. If x = y the function simply returns y. If either value is NaN, then NaN is returned. Otherwise a value corresponding to the value of the least significant bit in the mantissa is added or subtracted, depending on the direction.
The nexttoward() functions do the same as the nextafter() functions, except that they have a long double second argument.
CONFORMING TOC99. This function is defined in IEC 559 (and the appendix with recommended functions in IEEE 754/IEEE 854).