On Tue, 21 Sep 2021, Jakub Jelinek via Gcc-patches wrote: > On Tue, Sep 21, 2021 at 02:15:59PM +0100, Roger Sayle wrote: > > Can you double check? Integer division by zero is undefined, but isn't > > floating point > > division by zero defined by the appropriate IEEE standards? > > https://eel.is/c++draft/expr.mul#4 doesn't make the division by zero > behavior conditional on integral types. > C has similar wording.
The position for C is that Annex F semantics take precedence over all the ways in which floating-point arithmetic has undefined behavior in the main body of the standard. So floating-point overflow and division by zero are fully defined in the presence of Annex F support, while out-of-range conversions from floating point to integer types produce an unspecified value (not necessarily the same unspecified value for different executions of the conversion in the abstract machine - as discussed in bug 93806, GCC can get that wrong and act as if a single execution of such a conversion in the abstract machine produces more than one result). In C, as specified in Annex F, initializers for floating-point objects with static or thread storage duration are evaluated with exceptions discarded and the default rounding mode in effect; 7.0 / 0.0 is a fully valid initializer for such an object to initialize it to positive infinity. As I understand it, the question for this thread is whether C++ constexpr should have a similar rule to C static initializers (which ought to apply to 1.0 / 3.0, raising inexact, just as much as to 7.0 / 0.0). -- Joseph S. Myers jos...@codesourcery.com
