On Tue, 13 Oct 2015, Michael Meissner wrote: > I believe every non-NaN value that IBM extended double supports is > representable in IEEE 754R 128-bit floating point, since IEEE has 112 bits of > mantissa plus the hidden bit, while IBM extended double has 106 bits (52 bits > of mantissa for each part plus 2 hidden bits). Even with all of the extra bits
No, because IBM long double can represent values with discontiguous mantissa bits (these are the values that libgcc/config/rs6000/ibm-ldouble-format describes as denormal but not subnormal). > that you can hand craft into silent/signalling NaNs, you should be able > represent those values in IEEE 128-bit floating point as similar NaNs. The low part of a NaN in IBM long double is documented as don't-care (so all IBM long double NaNs are correctly converted to binary128 simply by converting the high part - as is also the case with zeroes). -- Joseph S. Myers jos...@codesourcery.com
