Date: Sun, 12 Aug 2012 23:09:23 -0000 From: Stephen Montgomery-Smith <stephen@missouri.edu> To: Bruce Evans <brde@optusnet.com.au> Cc: Diane Bruce <db@db.net>, John Baldwin <jhb@freebsd.org>, David Chisnall <theraven@freebsd.org>, Bruce Evans <bde@freebsd.org>, Steve Kargl <sgk@troutmask.apl.washington.edu>, David Schultz <das@freebsd.org>, Peter Jeremy <peter@rulingia.com>, Warner Losh <imp@bsdimp.com> Subject: Re: Use of C99 extra long double math functions after r236148 Message-ID: <50084322.7020401@missouri.edu> Resent-Message-ID: <20120812230916.GM20453@server.rulingia.com> In-Reply-To: <20120719205347.T2601@besplex.bde.org> References: <20120714120432.GA70706@server.rulingia.com> <20120717084457.U3890@besplex.bde.org> <5004A5C7.1040405@missouri.edu> <5004DEA9.1050001@missouri.edu> <20120717200931.U6624@besplex.bde.org> <5006D13D.2080702@missouri.edu> <20120718205625.GA409@troutmask.apl.washington.edu> <500725F2.7060603@missouri.edu> <20120719025345.GA1376@troutmask.apl.washington.edu> <50077987.1080307@missouri.edu> <20120719032706.GA1558@troutmask.apl.washington.edu> <5007826D.7060806@missouri.edu> <5007AD41.9070000@missouri.edu> <20120719205347.T2601@besplex.bde.org>
next in thread | previous in thread | raw e-mail | index | archive | help
This is a multi-part message in MIME format. --------------020105090904080608070404 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit On 07/19/2012 06:16 AM, Bruce Evans wrote: > On Thu, 19 Jul 2012, Stephen Montgomery-Smith wrote: > >> I did a ULP test on clog. The test code is attached. (Not the >> cleanest code, I know, but it does the job.) It needs the mpfr and >> unuran ports installed. >> >> To my shock, I found that under certain circumstances, the ULP in the >> real part was huge. The problem is when hypot(x,y) is close to 1, >> because then the real part of clog is close to zero. I was seeing >> ULPs in the thousands. > > Better than GULPs in the thousands :-). > > This is not the problem that I first thought it might be. > >> I struggled to find a solution, and now I think I have the ULP down to >> about 2. I am going to work on it more tomorrow to see if I can get >> ULP down even further. I have the ULP down to about 1.2 now. I don't see how I can do better, because I have to invoke log functions twice, and probably each one has a ULP of about 0.6. Also I decided to use 1/2 log(x*x+y*y) when x and y are not too large. I am really rather proud of how I got around the large ULP when hypot(x,y) is close to 1. I would be glad if any of you could look at the code when you get a chance. Also, now that I see how hard clog was, I have more appreciation of Steve's objections. --------------020105090904080608070404--
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?50084322.7020401>