standards/59797: Implement C99's round[f]() math fucntions

[Steven G. Kargl]

David Schultz wrote:
> On Fri, Jun 04, 2004, David Schultz wrote:
> > Sorry, I've put this off way too long.  The good news is that I'm
> > now going to do something about it.  The bad news is that I found
> > a significant bug in the proposed implementation.  Namely, round()
> > and roundf() often get the wrong answer for halfway cases.  In
> > IEEE-754 round-to-nearest mode, numbers that are halfway between
> > two representable numbers are supposed to be rounded to even.
> 
> It seems I've paged out more material from my brain than I thought
> since I last looked at this.  POSIX defines round() to
> specifically *not* use the IEEE-754 round-to-nearest behavior.
> Your implementation is absolutely correct, Steve, and it even gets
> the exception flags right.  (I tested all positive inputs to
> roundf(), probed inputs to round() uniformly at random for a few
> minutes, and checked important special cases.)  I'll go ahead and
> commit it with minor style and doc fixes.
> 

I would have to go back and review the PR for all the discussion,
but I thought bde had proposed using rint(3) with an appropriate
rounding mode.  Anyway, whatever you decide to do is fine with
me. 

BTW, thanks for the work on fenv.  Sorry, I couldn't provide a review.
I did look at your patch, but it was way over my head.

-- 
Steve
http://troutmask.apl.washington.edu/~kargl/