From: Sven Joachim <svenjoac@gmx.de>
To: Paul Eggert <eggert@cs.ucla.edu>
Cc: Emacs Development <Emacs-devel@gnu.org>
Subject: Re: Emacs using SSE2 on x86
Date: Sat, 04 Jul 2020 20:58:34 +0200 [thread overview]
Message-ID: <874kqn5cpx.fsf@turtle.gmx.de> (raw)
In-Reply-To: <cbd6afdd-f223-6679-e8f1-0b0a79ae0d64@cs.ucla.edu> (Paul Eggert's message of "Sat, 4 Jul 2020 09:27:11 -0700")
On 2020-07-04 09:27 -0700, Paul Eggert wrote:
> Bug#42147 reports that Emacs floating-point rounds differently on x86 than on
> all other platforms, and in its Message #104 I propose a patch to fix this by
> using GCC's -msse2 -mfpmath=sse options. This patch is needed on GNU/Linux
> systems; it should be irrelevant on macOS (where SSE2 has always been required)
> or on MS-Windows development systems (where SSE2 has been the default since 2012).
>
> The patch cajoles GCC and similar compilers into using 64-bit floating point
> instead of erratically substituting 80-bit floating point. Although using 80
> bits can improve accuracy, it means the numbers disagree with other platforms
> and (as Bug#42147 notes) this is more of a problem for Emacs than any lost accuracy.
>
> The patch relies on SSE2 instructions on the x86, which were introduced in 2000
> and which have by now become universal. I don't see a downside of requiring SSE2
> for GCC etc., because as far as I can see, in the GNU/Linux world the only
> people running 32-bit Emacs on Intelish platforms nowadays are using AMD64 Linux
> kernels and compiling with 'gcc -m32', and AMD64 requires SSE2 anyway. However,
> I thought I'd mention this on emacs-devel in case I'm missing something.
The Debian i386 port still uses older machines without SSE2 as its
baseline, and apparently there are some people who still use Pentium III
or Athlon XP machines, even for web browsing[1].
Whether you want to support them is up to you, but in general Emacs runs
very well even on such old hardware.
Cheers,
Sven
1. https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=877445
next prev parent reply other threads:[~2020-07-04 18:58 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-07-04 16:27 Emacs using SSE2 on x86 Paul Eggert
2020-07-04 18:58 ` Sven Joachim [this message]
2020-07-04 19:19 ` Eli Zaretskii
2020-07-04 23:07 ` Andrea Corallo via Emacs development discussions.
2020-07-04 21:10 ` [OFFTOPIC] " Stefan Monnier
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