https://gcc.gnu.org/bugzilla/show_bug.cgi?id=87390
--- Comment #16 from joseph at codesourcery dot com <joseph at codesourcery dot com> --- On Wed, 26 Sep 2018, vincent-gcc at vinc17 dot net wrote: > https://gcc.gnu.org/bugzilla/show_bug.cgi?id=87390 > > --- Comment #14 from Vincent Lefèvre <vincent-gcc at vinc17 dot net> --- > (In reply to jos...@codesourcery.com from comment #13) > > On Wed, 26 Sep 2018, vincent-gcc at vinc17 dot net wrote: > > > > > But there are no differences with 6.3.1.4 (when converting to a floating > > > type): > > > in both cases, either the value can be represented exactly, in which case > > > it is > > > unchanged, or it cannot, in which case it is rounded. When doing a > > > conversion > > > to some given type, the C standard does not care of the origin type of the > > > value. > > > > In 6.3.1.5 in C99, that distinction is only applied in the case of > > which distinction? The one you made above, between values that can be represented in the target type, and those that cannot and are thus rounded. > > demotions and explicit conversions (second paragraph); it does not apply > > in the first paragraph (implicit promotions). I.e., the 6.3.1.4 handling > > of conversions from integer to floating-point is analogous to the 6.3.1.5 > > second paragraph handling of demotions and explicit conversions from > > floating-point to floating-point (not to the first paragraph handling of > > implicit promotions). > > Analogous? Where does the C standard say that? It doesn't say so directly. Rather, if you apply your comparison (comment#12) of 6.3.1.4 and 6.3.1.5 ("in both cases, either the value can be represented exactly, in which case it is unchanged, or it cannot, in which case it is rounded"), I think it has to be one of 6.3.1.4 with 6.3.1.5 paragraph 2, and in 6.3.1.5 paragraph 2 there is no excess precision in the result of the conversion. I see no reason here, if someone has explicitly chosen an old standard mode (-std=c99), to deviate from the interpretations of ambiguities used since excess precision support was first added, given that the changes in C11 did not results from the Defect Report process but from a separate paper outside of that process.
