Date: Sun, 12 Aug 2012 23:08:24 -0000 From: Stephen Montgomery-Smith <stephen@missouri.edu> To: Peter Jeremy <peter@rulingia.com> Cc: Diane Bruce <db@db.net>, Steve Kargl <sgk@troutmask.apl.washington.edu>, John Baldwin <jhb@freebsd.org>, David Chisnall <theraven@freebsd.org>, Bruce Evans <bde@freebsd.org>, Bruce Evans <brde@optusnet.com.au>, David Schultz <das@freebsd.org>, Warner Losh <imp@bsdimp.com> Subject: Re: Use of C99 extra long double math functions after r236148 Message-ID: <5007403F.8000909@missouri.edu> Resent-Message-ID: <20120812230817.GD20453@server.rulingia.com> In-Reply-To: <20120718224222.GA6022@server.rulingia.com> References: <C527B388-3537-406F-BA6D-2FA45B9EAA3B@FreeBSD.org> <20120713155805.GC81965@zim.MIT.EDU> <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> <20120718224222.GA6022@server.rulingia.com>
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On 07/18/2012 05:42 PM, Peter Jeremy wrote: > On 2012-Jul-18 10:07:41 -0500, Stephen Montgomery-Smith <stephen@missouri.edu> wrote: >> I went on a long road trip yesterday, so I didn't get any code written, >> but I did have a lot of thoughts about clog and casinh. > > Can I suggest you have a read through "Implementing the Complex > Arcsine and Arccosine Functions Using Exception Handling" by > T. E. Hull Thomas F. Fairgrieve and Ping Tak Peter Tang, ACM > Transactions on Mathematical Software, Vol. 23, No. 3, September 1997. > Based on a quick skim, it includes fairly detailed pseudocode, > together with an error analysis. OK, I will do that. My pseudo code is different in that I use clog, and they do not. I'll probably go with my approach, but use lots of ideas from this paper as seems appropriate. I might even try both approaches and see which seems to be the winner, > > On 2012-Jul-18 16:09:06 -0500, Stephen Montgomery-Smith <stephen@missouri.edu> wrote: >> Am I to understand that the inexact flag should be set anytime a >> floating point operation produces an answer that is not guaranteed >> exact? > > My understanding is, yes. For the transcendental functions, that > means the inexact flag should almost always be raised and the problem > becomes when not to raise it. Eg sin(0) == 0 and presumably doesn't > set the inexact flag. > >> For example, should 1.0/3.0 and sqrt(2.0) raise the inexact flag? > > Yes and yes. I notice our sqrtl() actually tests the inexact flag of > an intermediate calculation to determine the correct rounding for the > result. Thank you for the clarification. I will definitely set the inexact flag under the circumstances pointed out by Steve. Otherwise, I will rely on clog and csqrt to set the inexact flag. (And clog will depend upon log, hypot and atan2 to set the inexact flag.)home | help
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