From: Alexander Monakov <amonakov@ispras.ru>
To: musl@lists.openwall.com
Subject: Re: [musl] Q: dealing with missing removal of excess precision
Date: Sun, 22 Mar 2020 20:40:19 +0300 (MSK) [thread overview]
Message-ID: <alpine.LNX.2.20.13.2003222022340.2534@monopod.intra.ispras.ru> (raw)
In-Reply-To: <20200322011958.GM11469@brightrain.aerifal.cx>
On Sat, 21 Mar 2020, Rich Felker wrote:
> With the fixups mentioned (included in attached patches), i386 and
> x86_64 are passing libc-test and seem fine. OK if I merge them
> (rebasing the fixups in as fixups)? With s/x86/x87/ naming?
Ack for x87 naming, fabsf fix and sqrt +0x300 fix.
Nack for sqrt 'unsigned short' fix, I recommend to consider
'unsigned fpsr = 0' and "+a" constraint, the resulting assembly is
much better (GCC doesn't seem to do a good job optimizing the 'unsigned short'
variant at all).
I also would like to see i386/sqrtf.c to explain why double rounding
is safe, either as a comment (my preference) or in the commit message.
I would write something like the following:
The long double result has sufficient precision so that second rounding
to float still keeps the returned value correctly rounded, see
Pierre Roux, "Innocuous Double Rounding of Basic Arithmetic Operations".
(this paper elaborates the earlier [currently paywalled] paper by Figueroa)
Actually, may I ask why the initial commit did not mention that it relies
on this nontrivial property?
Thanks.
Alexander
next prev parent reply other threads:[~2020-03-22 17:40 UTC|newest]
Thread overview: 55+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-01-05 16:35 math patches for moving bare asm to C inline asm Alexander Monakov
2020-01-05 16:36 ` [PATCH] math: move x86_64 fabs, fabsf to C with " Alexander Monakov
2020-01-05 20:05 ` Rich Felker
2020-01-05 21:32 ` Alexander Monakov
2020-01-05 22:43 ` Rich Felker
2020-01-06 8:17 ` Alexander Monakov
2020-01-06 8:40 ` [PATCH] math: move more x86-family fabs functions to C Alexander Monakov
2020-03-21 17:06 ` [musl] " Rich Felker
2020-01-06 16:50 ` [PATCH] math: move trivial x86-family sqrt " Alexander Monakov
2020-01-06 17:43 ` [PATCH] math: move i386 sqrtf " Alexander Monakov
2020-01-06 18:32 ` Pascal Cuoq
2020-01-09 15:55 ` Alexander Monakov
2020-01-09 17:00 ` Rich Felker
2020-01-09 21:00 ` Szabolcs Nagy
2020-01-09 22:00 ` Rich Felker
2020-01-09 23:18 ` Szabolcs Nagy
2020-01-10 2:07 ` Rich Felker
2020-01-10 9:17 ` Szabolcs Nagy
2020-01-14 17:59 ` [musl] " Alexander Monakov
2020-01-14 18:47 ` Szabolcs Nagy
2020-01-07 13:06 ` [PATCH] math: move i386 sqrt " Alexander Monakov
2020-01-08 7:26 ` Rich Felker
2020-03-21 17:53 ` [musl] " Rich Felker
2020-03-21 17:57 ` Rich Felker
2020-03-21 20:30 ` Alexander Monakov
2020-01-11 15:06 ` [PATCH] math: move x86_64 (l)lrint(f) functions " Alexander Monakov
2020-01-11 15:23 ` [PATCH] math: move more x86-family lrint " Alexander Monakov
2020-01-11 16:07 ` Rich Felker
2020-01-11 16:22 ` Rich Felker
2020-01-14 11:54 ` [musl] [PATCH] math: move x86-family rint " Alexander Monakov
2020-01-14 18:17 ` [musl] Q: dealing with missing removal of excess precision Alexander Monakov
2020-01-14 18:50 ` Szabolcs Nagy
2020-01-14 18:58 ` Rich Felker
2020-01-14 19:53 ` Alexander Monakov
2020-02-06 14:51 ` Rich Felker
2020-02-06 17:15 ` Alexander Monakov
2020-02-06 17:46 ` Rich Felker
2020-02-06 19:03 ` Rich Felker
2020-02-06 20:02 ` Rich Felker
2020-02-06 22:08 ` Szabolcs Nagy
2020-02-22 19:59 ` Rich Felker
2020-02-22 20:21 ` Alexander Monakov
2020-02-23 0:19 ` Rich Felker
2020-02-23 16:14 ` Alexander Monakov
2020-03-20 18:12 ` Rich Felker
2020-03-22 1:19 ` Rich Felker
2020-03-22 17:40 ` Alexander Monakov [this message]
2020-03-22 17:53 ` Rich Felker
2020-03-22 18:51 ` Alexander Monakov
2020-03-22 19:10 ` Rich Felker
2020-03-22 19:46 ` Alexander Monakov
2020-01-14 20:41 ` [musl] [PATCH] math: move x86-family remainder functions to C Alexander Monakov
2020-01-15 6:54 ` Szabolcs Nagy
2020-01-15 15:44 ` [musl] [PATCH] math: move x86-family fmod " Alexander Monakov
2020-01-16 21:00 ` [musl] [PATCH] math: add x86_64 remquol Alexander Monakov
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