Re: ***[Possible UCE]*** [PATCH] Special case math library fixes.

["Cary R." <cygcary at yahoo dot com>]

--- n8tm@aol.com wrote:
> log() and log10() of negative numbers should return
> NaN. The existing code was returning minus infinity,
> but NaN is a better choice when you consider that NaN
> often represents Not A real Number. The documentation
> in w_log.c was also changed to describe the new
> behavior. Other libraries produce NaN.
>
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> 
> Technically correct, of course, but not necessarily an improvement in
> practice.
> 
> Arguments such as -FLT_MIN < arg < 0.  are likely to be a result of
> normal
> 
> numerical roundoff, and then the -Inf result, or anything beyond
> log(DBL_MIN*DBL_EPSILON),
> 
> is easier to handle.
>
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Allowing very small negative numbers to also give minus infinity would not
be that hard to implement. The biggest problem is deciding what limit
value to use for the different cases (log/log10/logf/log10f). Though I
would argue that if someone is already handling -Inf it's not that much
more work to handle NaNs (Inf and NaN have identical exponent bit
patterns).

Cary

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