int a; …; (a == a) fails?

Question

if we set float and double type to NaN then they are not equal to anything including themselves.
can such a thing happens for

Answer 1

No. The comparation for floats is defines in such way, that NaN compared to any number will return false. Anyway, for ints there is another formula:

ZF = !(a ^ b);

That will give true for any possible value of a.

EDIT: on GCC, with any -O flag, the comparation just dissapears to true.