Date: Sat, 29 Nov 2003 08:31:05 -0800 From: Steve Kargl <sgk@troutmask.apl.washington.edu> To: freebsd-standards@FreeBSD.ORG Subject: Re: Implementing C99's roundf(), round(), and roundl() Message-ID: <20031129163105.GA32651@troutmask.apl.washington.edu> In-Reply-To: <20031129080911.GA25448@VARK.homeunix.com> References: <20031129000133.GA30662@troutmask.apl.washington.edu> <20031129080911.GA25448@VARK.homeunix.com>
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On Sat, Nov 29, 2003 at 12:09:11AM -0800, David Schultz wrote:
> On Fri, Nov 28, 2003, Steve Kargl wrote:
> > Can the math functions round[fl]() be implemented in
> > terms of other math(3) functions and still conform to the
> > C99 and POSIX standard? For example,
> >
> > #include <math.h>
> >
> > float roundf(float x) {
> > float t;
> > if (x >= 0.0) {
> > t = ceilf(x);
> > if ((t - x) > 0.5) t -= 1.0;
> > return t;
> > } else {
> > t = ceilf(-x);
> > if ((t + x) > 0.5) t -= 1.0;
> > return -t;
> > }
> > }
>
> This looks correct to me at first glance, modulo possible problems
> with overflow. It's valuable to have simple MI implementations of
> these functions to avoid hampering efforts to port FreeBSD to new
> architectures. Faster MD versions can always be added later. (I
> noticed the other day that Intel has actually released an
> optimized IA64 libm, which we should consider importing.)
I don't undrestand your overflow comment. ceil[f]() can return Inf
and nan, but in those cases round[f]() should also return Inf and nan.
The two operations, (t-x) and (t+x), should yield a value in the
range [0,1). I'll submit a PR with a man page.
As a side comment, we need to start coding the missing C99 math(3)
functions because GCC is moving to using these in their CVS
development trees.
--
Steve
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