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There are a few other very minor details that can vary between platforms: - In binary floating-point, implementations are allowed to "detect tininess" either "before" or "after rounding". ARM and PPC detect it before rounding, x86 detects it after. This only changes whether or not the underflow flag is set for results in a tiny 1/4-ulp-wide interval, and only effects multiplication, fma, and conversion (results from the other basic operations cannot land in that interval). Since almost no one cares about flags, this is not a big deal; if flush-to-zero is enabled, it will perturb results that land in this band, however. - implementations are allowed to set or not set the invalid flag for fma(0, inf, quiet nan). Again, almost no one cares about flags, so no problem, but if invalid is unmasked, this effects whether or not you trap. The bigger issue, as you say, is that C/C++ leave the width of intermediate expression evaluation up to the implementation (but the compiler has to say what it does via FLT_EVAL_METHOD, so you can refuse to compile if the compiler doesn't do what your program needs). |