[vlc-devel] commit: contrib: turn off Thumb ISA for libavcodec and libmad ( Rémi Denis-Courmont )

Rémi Denis-Courmont remi at remlab.net
Sat Aug 29 22:26:15 CEST 2009

Le samedi 29 août 2009 23:12:28 Rafaël Carré, vous avez écrit :
> On Sat, 29 Aug 2009 22:06:38 +0300
> "Rémi Denis-Courmont" <remi at remlab.net> wrote:
> > I guess avcodec uses fancy ASM instructions outside of Thumb-2.
> You can't use inline asm when asking GCC to build thumb because you
> don't know if it will use ARM or THUMB instruction set for a specific
> function.

AFAIK, it uses whatever it was told to for the current file.

> A solution would be to build the files containing inline ARM asm with
> -mno-thumb -mthumb-interwork but you'd have to check every file

That's what's currently done.

> Last but not least: thumb is quite limited and considered slower than
> ARM code (note thumb-2 appears to be generally faster than thumb) so
> it's not advised for multimedia routines especially when you have loads
> of memory available and code size doesn't matter that much.

I thought *flash* (not RAM) might be tight but we will see when the device is 
actually out.Otherwise, it's clear that Thumb, even Thumb-2, is pointless and 
I will remove it *then*.

At any rate, merging the avcodec and avformat plugin would be a much bigger 
gain than Thumb, and would also benefit "slightly" more common targets such 
as... Windows.

Rémi Denis-Courmont

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