(abs ) crash with NaN

[nigelbrown]

Giving newlisp 7.3.17

(abs (sqrt -1))

crashes newlisp -

so does

> (setq isnan (sqrt -1))

+NAN

> (NaN? isnan)

true

> (abs isnan)



I note in nl-math.c some code protects DIVIDE from Nan viz

#ifdef __BORLANDC__

         if(isnan(number))

            {

            result = number;

            break;

            }

#endif

         if(number == 0.0)

            return(errorProc(ERR_MATH));

         result /= number;

         break;



but not other functions

so (min (sqrt -1) 2) also "crashes".



I suspect it may relate to uncaught signals or exceptions from the math processor along the lines of the thread "math exception handling" http://www.alh.net/newlisp/phpbb/viewtopic.php?t=102">http://www.alh.net/newlisp/phpbb/viewtopic.php?t=102



I've not tested all functions as to susceptibility to NaN problems - you

can probably see from the code which ones are at risk. In leu of catching

the signals etc perhaps more checking for NaN along the lines above used for divide is needed for robustness.



Nigel

[Lutz]

this problem exists on Win32 but is fine on Linux/BSD where floating point functions on NaN return NaN.



In the upcoming 7.4.0 rc1 the Win32 version will behave the same way: All floating point operations on NaN return NaN. This is BTW also the same way Java is doing this. They have been very careful to offer a standard 'math' behaviour across platforms. The manual will also be changed accordingly.



NaN in an 'integer' context will still be treated like 0.



(+ 1 (sqrt -1)) => 0

(add 1 (sqrt -1)) => NaN



Lutz

[nigelbrown]

Hi Lutz

I don't know how much you should protect a programmer from the

consequences of doing 'silly' things?



(sequence 2 (sqrt -1))

will crash newlisp - NaN can be sooo bothersome.



Regards

Nigel

[Lutz]

thanks Nigel, for 7.4.0 both 'sequence' and 'series' will return an empty list () when NaNs are passed as parameters. The () works like nil in boolean contexts: if, while etc.



Lutz

[Lutz]

correction to previous post:



in 'sequence', 'series', 'for', 'dotimes' NaN in a parametere will cause an "invalid parameter" error message.





Lutz