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Re: Refine documentation of libm exceptions goals [committed]

On Wed, 18 Feb 2015, Szabolcs Nagy wrote:

> * Joseph Myers <> [2015-02-18 17:25:38 +0000]:
> > On Wed, 18 Feb 2015, Szabolcs Nagy wrote:
> > 
> > > this is an interesting issue because iso c annex f forbids the
> > > omission of underflow right now, which is hard to achive unless
> > > libm checks <= DBL_MIN instead of the sensible < DBL_MIN and
> > > raises spurious underflow for a lot of exact (or non-tiny) DBL_MIN
> > > results (which is allowed by the standard)
> > 
> > I don't believe it forbids computing an imprecise result that happens to 
> > be (exactly) DBL_MIN or more, and so doesn't underflow.
> > 
> well, there are no precision requirements on not exactly-defined math
> functions, but with that interpretation an implementation which never
> raises underflow is also correct: it can claim that it exactly computed
> an incorrect result so there is no precision loss and thus no underflow

Yes.  This falls under the general implementation-defined accuracy of libm 

Joseph S. Myers

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