On 01/16/2013 01:28 PM, Robert Dewar wrote:
On 1/16/2013 7:10 AM, Mischa Baars wrote:
And as I have said before: if you are satisfied with the answer '2',
then so be it and you keep the compiler the way it is, personally I'm am
not able to accept changes to the sources anyway. I don't think it is
the right answer though.
The fact that you don't think that gcc shoudl follow the C standard
is hardly convincing unless it is backed up by convincing technical
argument. I see nothing surprising about the 2 here, indeed any other
answer *would* be surprising. I still don't understand the basis for
your non-stnadard views.
Mischa.
Let me explain again for you. Every 'if' statement in C is translated
into a 'fucom' or similar instruction, which sets a number of conditions
flags in the co-processor. Some instructions need you to load these into
the eflags register manually, others don't.
Now, as soon as the 'fucom' or similar instruction encounters a
'signalling not-a-number' or 'quiet not-a-number' as one or both of it's
arguments, the condition code is set to 'not comparable'. This has
nothing to do with the C specification, but purely with the Intel/AMD
hardware.
If you ask me, it would be counter-intuitive to change the value of the
condition code to some other value and call that the new standard.
Instead it would seem logical to use the 'not comparable' and terminate
the 'if' statement.
Does that make sense to you?
In our example, a 'not-a-number' would be returned to the main program,
without the need for an extra 'isnan()'.
Mischa.
