[vlc-devel] [vlc-commits] Avcodec: set the dsp_mask for NEON too

Måns Rullgård mans at mansr.com
Tue Oct 2 01:19:29 CEST 2012

Jean-Baptiste Kempf <jb at videolan.org> writes:

> On Mon, Oct 01, 2012 at 11:45:40PM +0100, Måns Rullgård wrote :
>> Because runtime CPU detection on ARM is not generally possible (some
>> systems expose a subset of the information we need), we rely on probing
>> the compiler settings to determine which code to build and use.
> The information of having NEON or not is not enough?

Obviosly not.  You need to know about armv5te, armv6, armv6t2, vfp,
vfpv3, vfpv3-d32, neon, etc.  Some of these are reported in Linux hwcaps
(listed in /proc/cpuinfo) but not all.

>> Furthermore, even if runtime detection is possible, you still want to
>> build with the compiler flags best matching the target device.  Compared
>> to x86, much greater gains are made in plain C code when building for
>> the actual target hardware rather than something less capable.
> Sure, but can't one do a "average" binary (not best match) to work on
> all cortex-a8 and a9 and just activate NEON code when a NEON fpu is present?
> Or am I too naive?


Måns Rullgård
mans at mansr.com

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