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From: Rich Felker <dalias@libc.org>
To: musl@lists.openwall.com
Subject: Re: [musl] Q: dealing with missing removal of excess precision
Date: Tue, 14 Jan 2020 13:58:35 -0500	[thread overview]
Message-ID: <20200114185835.GG30412@brightrain.aerifal.cx> (raw)
In-Reply-To: <20200114185058.GV23985@port70.net>

On Tue, Jan 14, 2020 at 07:50:58PM +0100, Szabolcs Nagy wrote:
> * Alexander Monakov <amonakov@ispras.ru> [2020-01-14 21:17:55 +0300]:
> > What to do with functions that return values with excess precision from asm?
> > 
> > Many of the remaining x87-based asm implementations do not remove excess
> > precision on return. This looks like a bug, but matches Glibc behavior.
> > Moving such functions to C would either introduce removal of excess precision,
> > or result in code that lies to the compiler by pretending that inline asm keeps
> > values within precision of float/double, where in reality it might not.
> 
> the intention is to remove excess precision so it's good that's happening.

Agreed. It may be a slight performance regression but it's the right
thing to do anyway.

> otoh it would be nice if there was a way to tell the compiler not to
> remove it (e.g. in case the asm already took care of it) even in c99
> standard mode.

Perhaps this happens if the output constraint is tied to a float
rather than a long double?

Rich

  reply	other threads:[~2020-01-14 18:58 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 [this message]
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
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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