[FFmpeg-devel] [PATCH] avcodec/wmalossless: use av_clip_intp2

[Reimar Döffinger]

On Sun, Mar 08, 2015 at 10:32:03PM +0100, Michael Niedermayer wrote:
> On Sat, Mar 07, 2015 at 11:44:10PM +0800, zhaoxiu.zeng wrote:
> > From 47c997fa0623ab94a7a93b2d2e4cc4fa64c85d5f Mon Sep 17 00:00:00 2001
> > From: Zeng Zhaoxiu <zhaoxiu.zeng at gmail.com>
> > Date: Sat, 7 Mar 2015 23:26:42 +0800
> > Subject: [PATCH 1/1] avcodec/wmalossless: use av_clip_intp2
> 
> this breaks build on ARM
> 
> ffmpeg/libavutil/arm/intmath.h:69:5: warning: asm operand 2 probably doesn’t match constraints
> ffmpeg/libavutil/arm/intmath.h:69:5: warning: asm operand 2 probably doesn’t match constraints
> ffmpeg/libavutil/arm/intmath.h:69:5: error: impossible constraint in ‘asm’
> ffmpeg/libavutil/arm/intmath.h:69:5: error: impossible constraint in ‘asm’

ARM uses asm code based on the ssat instruction.
That one requires the number of bits to be a constant.
This means that for ARM this function may only be used with constant
p argument.
I guess whether this is ok depends on whether there are other
cases/architectures where av_clip_intp2 is actually faster than a
normal clip even when p is not constant.
The C code doesn't look particularly faster to me in that case,
but I haven't tested it.