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Date: Wed, 7 Aug 2019 21:46:06 -0400
From: Rich Felker <dalias@...c.org>
To: musl@...ts.openwall.com
Subject: Re: new exp fails erfc in libc-test

On Wed, Aug 07, 2019 at 05:47:54PM -0700, Dan Gohman wrote:
> As of the patch which introduced the new exp implementations:
> 
> http://git.musl-libc.org/cgit/musl/commit/?id=e16f7b3c02e17d0ace779a11f0d53a9c05fdd434
> 
> I am seeing a test failure in the erfc test in libc-test on at least x86-64
> (erfc calls exp internally):
> 
> src/math/special/erfc.h:6: RN erfc(0x1.5db559fe5c0bap+0) want
> 0x1.b53cf571d328fp-5 got 0x1.b53cf571d328cp-5 ulperr -2.609 = -0x1.8p+1 +
> 0x1.900982p-2
> 
> Please let me know if there's any other information which would be useful.

I think errors on this order of magnitude are considered normal for
the transcendental functions. Is there something you're concerned will
break due to the difference in accuracy here, or are you asking if
it's potentially something you should be concerned about?

Rich

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