https://gcc.gnu.org/bugzilla/show_bug.cgi?id=87247
--- Comment #3 from kargl at gcc dot gnu.org --- (In reply to kargl from comment #2) > (In reply to Andrew Pinski from comment #1) > > I think there are two issues here, one is the glibc also puts the result in > > the wrong quadrant. The other issue is the GCC's constant folding does too. > > What is interesting is they both put in the same quadrant though. > > > > I cannot comment if this is a bug because I don't have a copy of the IEEE > > spec and/or C11 spec too. > > It's a bug in the Fortran Standard. OP should send an interpretation > request to J3. n1256.pdf has > > 7.3.6 Hyperbolic functions > > 7.3.6.1 The cacosh functions > > The cacosh functions compute the complex arc hyperbolic cosine > of z, with a branch cut at values less than 1 along the real axis. > > The cacosh functions return the complex arc hyperbolic cosine value, > in the range of a half-strip of non-negative values along the real > axis and in the interval [-i pi, +i pi] along the imaginary axis. Checking FreeBSD libm sources, which differ from glibc, one finds the comment /* * cacosh(z) = I*cacos(z) or -I*cacos(z) * where the sign is chosen so Re(cacosh(z)) >= 0. */ which means libm chooses the Riemann sheet with the REAL part always positive. Fortran must be using a convention for choosing a different Riemann sheet such that AIMAG part is always positive.
