http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57675
--- Comment #2 from joseph at codesourcery dot com <joseph at codesourcery dot com> --- N1399 has a detailed analysis of issues with complex multiply and divide in C99. There was no consensus to adopt requirements in that detail, but N1496 was adopted with a more minimal fix for (1.0+1.0*I)/(0.0+NAN*I). It appears that the GCC implementation does not suffer the particular issue being addressed in N1496. http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1399.txt http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1496.htm I believe the model in N1399 (and more generally for NaNs in C99/C11 and the draft TS 18661 bindings to IEEE 754-2008; see e.g. how hypot(NaN, Inf) works) is that NaN+1.0i is considered (for a quiet NaN) to be <unspecified-real>+1.0i. Dividing by zero then gives an unspecified (or not fully specified) infinity, so a result with one part infinity and one part NaN seems appropriate.
