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Chris B wrote:

> news:44281e86$1@news.povray.org...
> 
>>Those kind of numbers are
>>usually generated by the floating point hardware and the code that
>>writes them as the string "QNAN" is in the standard C library, so a
>>search through the povray code shouldn't turn up anything...
>>
>>Jerome
>>
> 
> 
> Ah OK.
> Well is there something Tim could do to detect this from within POV-Ray 
> before writing it out to the file?
> 
	Not that I know. The C99 standard defines the "isfinite",
"isnormal", "isnan" and "isinf" functions to check for this kind of
numbers but AFAIK there are no SDL equivalent.

> I had one idea. Don't know if it's valid or whether it might be a stupid 
> idea, but , if it's an intermittent problem with the FPU (an overflow or 
> something), then could he perform each calculation twice and compare the 
> results? (either with a numeric comparison or converting the numbers to 
> strings)
> 
	In most cases, performing the same computation twice should give
the same result. Moreover, the equality test isn't a solution: I
don't remember what the standard says but gcc with the -ffast-math
option will give nan==1. Now, I know that the -ffast-math option
breaks the standards (it says so in the docs), but I also know that
VisualC breaks them too and I don't know whith what options Tim's
version of POV was compiled...

		Jerome
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