------- Comment #22 from dominiq at lps dot ens dot fr 2008-10-31 12:52 ------- > One can argue that a NaN real(4)->real(8) conversion is OK or that it is > invalid - I think one can find arguments for both; in any case NaN can be > unambiguously converted from one real/complex to another real/complex kind.
I disagree with the last sentence since there in not a single (or dual if you take into account signaling NaN's) NaN entity, but a whole class of them. So if you accept the conversion, it should be defined: for instance, for REAL(4)->REAL(8) copy the mantissa to the upper/lower bits of the mantissa, or fold all of them to a zero mantissa but for the LSB, ... . I have never read anything about the reasons for having such a wide class of NaN's nor seen any use of it (even the use of quiet/signaling NaN's is quite fuzzy in most compiler implementation). -- http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37930
