[fpc-pascal] math with infinity and NaN

[gtt at wolfgang-ehrhardt.de]

This is compatible with IEEE-754.  Section 7.2 says

<quote>
7.2 Invalid operation

For operations producing results in floating-point format, the default  
result of an operation that signals the
invalid operation exception shall be a quiet NaN that should provide  
some diagnostic information (see 6.2).
These operations are:

...
b) multiplication: multiplication(0, ∞) or multiplication(∞, 0)

...

d) addition or subtraction or fusedMultiplyAdd: magnitude subtraction  
of infinities, such as:
addition(+∞, −∞)

e) division: division(0, 0) or division(∞, ∞)

...

g) squareRoot if the operand is less than zero
</quote>

You get the expected quite NaN results if you add the line

SetExceptionMask([exInvalidOp, exDenormalized, exZeroDivide,  
exOverflow, exUnderflow, exPrecision]);

to your test programs.