http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21718
--- Comment #15 from joseph at codesourcery dot com <joseph at codesourcery dot com> 2012-11-05 20:49:24 UTC --- The glibc code is pretty complicated (using glibc's copies of mpn_* low-level GMP functions for multiple-precision arithmetic) and entangled with other bits of glibc (it needs to handle things such as locales / thousands grouping characters, which are not relevant to GCC). And of course there is no guarantee that the host has any floating-point type corresponding to the required type on the target. Even working around the absence of a reliable ternary value in some supported MPFR versions, using MPFR for this would be much simpler than adapting the glibc code for use in GCC - it's the natural thing to do, given the use of MPFR for built-in function evaluation in GCC. (MPFR should also be used to replace real_sqrt - real.c doesn't use enough bits internally to get a correctly rounded sqrt result in all cases. fold_builtin_sqrt already does use mpfr_sqrt.)
