[fpc-pascal] math with infinity and NaN

[gtt at wolfgang-ehrhardt.de]

Quoting James Richters <james at productionautomation.net>:

> SetExceptionMask(GetExceptionMask + [exInvalidOp]);   Works!     
> Thank  you for the help!
>
> I'm curious why things like SQRT(-1) just produce NAN without  
> needing to change the exception mask and (+inf) - (+inf) does not  
> behave the same way.  They both are invalid,  why treat one method  
> of generating an invalid number one way and another method of  
> getting just as invalid of a number another way?  If there is  
> flexibility in the standard, then why not choose to always be  
> consistent?    I have a lot of examples of things that do produce  
> NAN without needing to change the exception mask... like ln(-1) or  
> 0/0  why do some cause the exception and others do not?

The case SQRT(-1) seems to be handled by the compiler, just like the  
definition
Nan = 0/0 in math.

If you have an expression, which is not handled at compile time you get
the EInvalidOp exception, try

variable2 := Pi-4;
variable1 := sqrt(variable2);
Writeln(variable1);