Date: Wed, 2 Jun 2004 01:43:13 -0700 From: David Schultz <das@FreeBSD.ORG> To: Bruce Evans <bde@zeta.org.au> Cc: freebsd-i386@FreeBSD.ORG Subject: Re: i386/67469: src/lib/msun/i387/s_tan.S gives incorrect results for large inputs Message-ID: <20040602084313.GA6912@VARK.homeunix.com> In-Reply-To: <20040602172105.T23521@gamplex.bde.org> References: <200406012251.i51MpkkU024224@VARK.homeunix.com> <20040602172105.T23521@gamplex.bde.org>
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On Wed, Jun 02, 2004, Bruce Evans wrote: > > >Fix: > > One solution might involve doing the reduction using > > __ieee754_rem_pio4() instead of the fprem1 instruction. > > Unfortunately, since this uses pi/2 as the modulus, it > > is necessary to apply the identity tan(x + pi/2) = -1/tan(x) > > for odd-phase inputs. I tried this for the first example > > input above and got an answer that was off by 2 ulps. Close, > > but the MI implementation gets within 1 ulp. I'm not sure what > > kind of correction (if any) should be used here. > > I think the complete fdlibm version of tan(), sin() and cos() should > be used for large args. "large" could be classified by failure of the > first fptan. Or just return the TLOSS error for very large args. I was hoping it could be fixed without the bloat, but your solution is clean and easy to implement...
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