IEEE 754-1985 had a nextAfter function (which C implemented them as nextafter and nexttoward), but that was removed in IEEE 754-2008 in favor of nextUp and nextDown, which C implemented as nextup and nextdown, but only as of C23, which still hasn't officially been published by ISO.
There's also another wrinkle: next* functions go from -subnormal to -0 to subnormal, and don't give you an iteration for both -0 and +0, which can be useful for some iteration purposes.
There's also another wrinkle: next* functions go from -subnormal to -0 to subnormal, and don't give you an iteration for both -0 and +0, which can be useful for some iteration purposes.