C extension + libm oddity [fmod(2.0, 2.0) == nan ?!]

Paul Rubin http
Sat Nov 5 02:13:26 CET 2005


"Lonnie Princehouse" <finite.automaton at gmail.com> writes:
> Now, fmod(2.0, 2.0) should be 0.0.   The problem? ans is getting
> assigned nan!  I have stepped through it in the debugger now dozens of
> times.  Either fmod is putting the wrong return value on the stack, or
> the stack is getting corrupted by something else and "ans" is getting
> assigned the wrong value.

Have you compiled the C extension with all optimization turned off?
Especially with optimizations on, you can't really tell what is going
to get assigned in a variable because the code isn't computing the
intermediate values you might expect it to.  I suggest disassembling
it and stepping through it instruction by instruction if you haven't
done that.



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