Date: Sun, 13 Feb 2005 18:10:36 GMT From: David Schultz <das@FreeBSD.ORG> To: freebsd-i386@FreeBSD.org Subject: Re: i386/67469: src/lib/msun/i387/s_tan.S gives incorrect results for large inputs Message-ID: <200502131810.j1DIAaIP037794@freefall.freebsd.org>
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The following reply was made to PR i386/67469; it has been noted by GNATS. From: David Schultz <das@FreeBSD.ORG> To: Bruce Evans <bde@zeta.org.au> Cc: FreeBSD-gnats-submit@FreeBSD.ORG, freebsd-i386@FreeBSD.ORG, bde@FreeBSD.ORG Subject: Re: i386/67469: src/lib/msun/i387/s_tan.S gives incorrect results for large inputs Date: Sun, 13 Feb 2005 13:08:37 -0500 On Mon, Feb 14, 2005, Bruce Evans wrote: > It seems that the hardware trig functions aren't worth using. I want > to test them on a 486 and consider the ranges more before discarding > them. This may take a while. Fair enough. I would be happy to have a hybrid implementation that uses the hardware only when appropriate. However, your 486 benchmarks notwithstanding, I would just as soon rely on fdlibm entirely for the trig functions. It just doesn't seem worthwhile to me, given that the only parts of the domain where the hardware is faster *and* correct are, roughly speaking, [0,2^-28) and [pi/4,pi/2-eps]. > I did a quick test of some other functions: > - hardware sqrt is much faster > - hardware exp is slightly faster on the range [1,100] > - hardware atan is slower on the range [0,1.5] > - hardware acos is much slower (139 nsec vs 57 nsec!) on the range [0,1.0]. sqrt isn't transcendental, so it should be faster and correctly rounded on every hardware platform. I found similar results to yours for atan() and acos() when writing amd64 math routines, but of course amd64 has the overhead of switching between the SSE and i387 units. Maybe they should go away, too...
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