On Mon, 30 Oct 2017, Wilco Dijkstra wrote: > Richard Biener wrote: > > Should we also get the __ieee764_ entries used if the compiler sets > > __NO_MATH_ERRNO__? That is, if the librari advertises not setting errno > > via math_errhandling is it still allowed to set/clobber errno anyways? > > That's a good question! I checked and the math wrappers currently use > __FINITE_MATH_ONLY__ to decide whether to use the IEEE754 version > or the wrapper which sets errno. However that's actually incorrect given > that the only purpose of the wrappers is to set errno, not to add IEEE > handling (which is done in the math implementation).
The semantics of __*_finite definitely include finite-math-only, as they aren't all just disabling the wrappers (e.g. sysdeps/i386/i686/fpu/e_log.S has __log_finite separate from __ieee754_log). > Note -ffinite-math-only appears to imply -fno-math-errno, eventhough > this is not clear from the documentation - is that expected? In principle > these options are orthogonal, setting errno due to a range error is still > valid even if you don't use infinities or NaNs. Well, it's expected for glibc (as an empirical observation about what the __*_finite entry points do). It may not necessarily be an implication for GCC. And given appropriate documentation, it doesn't necessarily contradict math_errhandling & MATH_ERRNO being nonzero (in that errno setting on underflow is implementation-defined in that case - glibc documents semantics involving setting errno on underflow to 0 but not necessarily otherwise, but could document the effects of -ffinite-math-only potentially disabling the errno setting on underflow to 0). -- Joseph S. Myers jos...@codesourcery.com
