On Mon, Oct 19, 2009 at 10:21:01AM +0200, Jonas Maebe wrote:
>
> On 18 Oct 2009, at 17:52, Tom Verhoeff wrote:
>
>> It would be nicer if one had the ability to make floating-point
>> division
>> by zero return an IEEE 754 plus/minus infinity, without raising an
>> exception.
>
> http://www.freepascal.org/docs-html/rtl/math/setexceptionmask.html
>
> Fully cross-platform, even.
How new is that?
It works 'partly'. Consider the program
program DivideByZero;
{ to see whether division by zero can result in Infinite values }
uses Math;
var one, zero, result: Double;
begin
SetExceptionMask ( [ exZeroDivide{, exPrecision} ] );
one := 1.0;
zero := 0.0;
result := one / zero;
writeln ( result ); { Expected output: +Inf }
result := one / result;
writeln ( result ); { Expected output: +0.0 }
end.
Outputs:
+Inf
An unhandled exception occurred at $000060B0 :
EDivByZero : Division by zero
$000060B0
$00005850
$0001889B
In order to allow 1 / +Inf, you also need to mask exPrecision
(i.e. uncomment it from the set passed to SetExceptionMask).
I am surprised that division by an Infinity raises EDivByZero: Division by zero
Best regards,
Tom
--
E-MAIL: T.Verhoeff @ TUE.NL | Dept. of Math. & Comp. Science
PHONE: +31 40 247 41 25 | Technische Universiteit Eindhoven
FAX: +31 40 247 54 04 | PO Box 513, NL-5600 MB Eindhoven
http://www.win.tue.nl/~wstomv/ | The Netherlands
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