https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85992
Richard Biener <rguenth at gcc dot gnu.org> changed: What |Removed |Added ---------------------------------------------------------------------------- Status|UNCONFIRMED |RESOLVED Resolution|--- |INVALID --- Comment #1 from Richard Biener <rguenth at gcc dot gnu.org> --- You get the runtime value computed by libm when not optimizing and the mpfr result when GCC applies constant folding. Iff then this is a libm bug not providing an exact result - but this is expected as you are dealing with FP.