http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21718
--- Comment #27 from Joseph S. Myers <jsm28 at gcc dot gnu.org> --- No, it was lack of precision. MPFR may need to use many more than SIGNIFICAND_BITS internally in order to compute a result that is correctly rounded towards zero to SIGNIFICAND_BITS (plus the ternary value), but GCC doesn't need to know or care how many bits MPFR uses; all it needs to know is that SIGNIFICAND_BITS is at least 2 more than the largest number in any supported binary floating-point format. Having got the C11 features I wanted into 4.9 I then looked for bugs on my list of conformance issues that would be more suited to development stage 1 (ends today) than to subsequent stabilization stages. This was one.
