https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114018
--- Comment #15 from Jonathan Wakely <redi at gcc dot gnu.org> --- (In reply to Jakub Jelinek from comment #13) > Then I wonder what was the reason for the final LWG3790 revision, the middle > proposed resolution seems to be much more readable and understandable where > one could see exactly what is valid in the synopsis and if the standard > attempts to save lines, > the extra 2 lines in the synopsis are the same size as the extra paragraph > hidden at the end. Ah, I've checked the minutes, and the reason for the final form of the wording is that we wanted to prevent: std::nexttoward((std::float32_t)0, 0.0L) With the three overloads for float/double/long double (as implemented in libstdc++ today) that would be well-formed if float is IEEE binary32. There is an implicit conversion to float, but that means it returns a float, not a _Float32 as you would expect it to. Similarly for nexttoward((std::float64_t)0, 0.0L). So we do need a change here, because we need to explicitly make that ill-formed. Maybe just (with suitable preprocessor checks for the types): void nexttoward(float32_t, long double) = delete; void nexttoward(float64_t, long double) = delete; void nexttoward(float128_t, long double) = delete; We could also add deleted overloads for bfloat16_t and float16_t although they don't currently compile anyway, because the float/double/long double overloads are ambiguous. For consistency in diagnostics, I think defining them all as deleted would be better.
