Date: Sun, 12 Aug 2012 23:13:03 -0000 From: Peter Jeremy <peter@rulingia.com> To: Stephen Montgomery-Smith <stephen@missouri.edu> Cc: Diane Bruce <db@db.net>, Bruce Evans <brde@optusnet.com.au>, 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>, Warner Losh <imp@bsdimp.com> Subject: Re: Use of C99 extra long double math functions after r236148 Message-ID: <20120721043052.GB73662@server.rulingia.com> Resent-Message-ID: <20120812231256.GX20453@server.rulingia.com> In-Reply-To: <500A139D.2090803@missouri.edu> References: <20120719205347.T2601@besplex.bde.org> <50084322.7020401@missouri.edu> <20120720035001.W4053@besplex.bde.org> <50085441.4090305@missouri.edu> <20120720162953.N2162@besplex.bde.org> <20120720184114.B2790@besplex.bde.org> <50097128.6030405@missouri.edu> <20120721032448.X5744@besplex.bde.org> <500A0DCF.4030707@missouri.edu> <500A139D.2090803@missouri.edu>
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--MW5yreqqjyrRcusr Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On 2012-Jul-20 21:27:41 -0500, Stephen Montgomery-Smith <stephen@missouri.e= du> wrote: >The way they handle the real part of clog(z), log(hypot(x,y)), when=20 >hypot(x,y) is close to 1, is to do the calculation in double precision.=20 > So to do it properly, we need a double double precision arithmetic,=20 >which we don't have. Actually, we do. r230363 includes both extended and quad long-double emulation code in lib/libc/softfloat. There's also ld128 code under lib/libc/sparc64/fpu. >The paper says that simulating double precision arithmetic using single=20 >arithmetic is slow, so I would think the same is true for quad-precision. It depends how much af the arithmetic needs to be in more-than-double precision. Possibly, careful choice of partitioning would allow double precision to be used for most values with multi-precision only needed some of the time. I expect catanh() will run into similar problems evaluating clog((1 + z)/(1 - z)). Something like clog1p() would help when z=20 is close to 1, as will using alternative expansions. >Does the inexact flag also raise the SIGFPE signal? It's under program control - see feenableexcept() and fedisableexcept(), --=20 Peter Jeremy --MW5yreqqjyrRcusr Content-Type: application/pgp-signature -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.19 (FreeBSD) iEYEARECAAYFAlAKMHwACgkQ/opHv/APuIdDewCfdQfziJIblEBpobdLeISWPnRV OUcAoMDn0liv1DgjH4J8NmH2xnXSPcAe =NIRR -----END PGP SIGNATURE----- --MW5yreqqjyrRcusr--
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