On Thu, Jan 02, 2014 at 09:46:56PM +0000, Joseph S. Myers wrote: > (Note that there remain other bugs in the IBM long double code, some > causing glibc test failures, at least (a) invalid results in rounding > modes other than FE_TONEAREST, (b) spurious overflow and underflow > exceptions, mainly but not entirely where discontiguous mantissa bits > are involved.)
Thing is, the algorithms in rs6000/ibm-ldouble.c require round to nearest to generate correct results. Quoting from the PowerPC64 ABI: This "Extended precision" differs from the IEEE 754 Standard in the following ways: * The software support is restricted to round-to-nearest mode. Programs that use extended precision must ensure that this rounding mode is in effect when extended-precision calculations are performed. * Does not fully support the IEEE special numbers NaN and INF. These values are encoded in the high-order double value only. The low-order value is not significant. * Does not support the IEEE status flags for overflow, underflow, and other conditions. These flag have no meaning in this format. -- Alan Modra Australia Development Lab, IBM
