From: Joseph Myers <joseph@codesourcery.com>
To: Szabolcs Nagy <Szabolcs.Nagy@arm.com>
Cc: Anssi Hannula <anssi.hannula@bitwise.fi>,
"libc-alpha@sourceware.org" <libc-alpha@sourceware.org>,
nd <nd@arm.com>
Subject: Re: [PATCH 1/2] ieee754: Remove slow paths from asin and acos
Date: Tue, 24 Mar 2020 23:15:08 +0000 [thread overview]
Message-ID: <alpine.DEB.2.21.2003242314560.8310@digraph.polyomino.org.uk> (raw)
In-Reply-To: <714b667d-7345-bcd4-ca30-7ecbb7098bbc@arm.com>
On Mon, 27 Jan 2020, Szabolcs Nagy wrote:
> On 27/01/2020 10:45, Anssi Hannula wrote:
> > asin and acos have slow paths for rounding the last bit that cause some
> > calls to be 500-1500x slower than average calls.
> >
> > These slow paths are rare, a test of a trillion (1.000.000.000.000)
> > random inputs between -1 and 1 showed 32870 slow calls for acos and 4473
> > for asin, with most occurrences between -1.0 .. -0.9 and 0.9 .. 1.0.
> >
> > The slow paths claim correct rounding and use __sin32() and __cos32()
> > (which compare two result candidates and return the closest one) as the
> > final step, with the second result candidate (res1) having a small offset
> > applied from res. This suggests that res and res1 are intended to be 1
> > ULP apart (which makes sense for rounding), barring bugs, allowing us to
> > pick either one and still remain within 1 ULP of the exact result.
> >
> > Remove the slow paths as the accuracy is better than 1 ULP even without
> > them, which is enough for glibc.
> >
> > Also remove code comments claiming correctly rounded results.
>
> the patch looks good to me.
Yes, please commit.
--
Joseph S. Myers
joseph@codesourcery.com
next prev parent reply other threads:[~2020-03-24 23:15 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-01-27 10:45 Anssi Hannula
2020-01-27 11:25 ` [PATCH 2/2] ieee754: Remove unused __sin32 and __cos32 Anssi Hannula
2020-01-27 13:12 ` [PATCH 1/2] ieee754: Remove slow paths from asin and acos Szabolcs Nagy
2020-01-28 10:51 ` Anssi Hannula
2020-03-24 23:15 ` Joseph Myers [this message]
2020-12-18 7:09 ` [COMMITTED] " Siddhesh Poyarekar
2020-12-18 8:28 ` Paul Zimmermann
2020-12-18 9:26 ` Siddhesh Poyarekar
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