Exception when casting doubles to ints

alan buckley alan_baa at hotmail.com
Fri Jan 7 01:11:06 PST 2005

>John Tytgat wrote:
>In message <BAY101-F254E3ED3F8DDFE11900C51F0930 at phx.gbl> you wrote:
> > It appears that when a double that is larger than the maximum
> > int is cast to an int a floating point exception occurs. On cygwin
> > you do not get an exception, and as the code where I found the
> > problem was in lua I suspect other linux/unix variations also do not
> > raise an exception. Can anyone confirm the unix behaviour?
> >
> > If this is the case should the RISC OS gcc match what unix does?
>Actually I don't mind this being the default behaviour because it is
>something pretty undefined what int value you would have if no exception
>would be raised.

The default behaviour does make sense to me as well. However it does
appear that it may be different from the behaviour generated by GCC on
other machines.

>But I think your question is around the header fenv.h (cfr.
>for more info).  I understand from it that the default floating point
>exception behaviour is not specified but that you can change it with
>limitations using the fe*() functions.  If your lua program is using
>those fe*() and you think UnixLib is not behaving like the above mentioned
>specification, feel free to let us know the details.

The lua program and the test program I included don't use the fenv.h 
at all. Having looked at the documentation above I can't see how they help
as they seem to be just setting and getting the status registers and not
modifying the behaviour.

Have I misread the documentation? If so, can you show me the code I
need to add to a program?

If not, is there any other routine I can add to the program to modify how
casting from double to int is handled.


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