[FFmpeg-devel] [PATCH] libswscale/x86/yuv2rgb: Add missing EMMS

Michael Niedermayer michael at niedermayer.cc
Tue Jun 25 23:09:23 EEST 2024


On Tue, Jun 11, 2024 at 05:19:06PM +0000, Mario Hros wrote:
> Ping?
> 
> Not including EMMS causes the FPU to become unusable (as the IE and SF bits are set in the status word). This breaks code which, for instance, calls fmod() and is compiled by GCC with the -O3 flag enabled. In that scenario, GCC implements fmod using the FPREM FPU instruction, but because FPU is in the invalid state at that point, the result is NaN.
> 
> This must to breaking other code using FPU also. The original code with inline assembly used EMMS at the end.
> ________________________________
> From: Mario Hros <k3x-devel at outlook.com>
> Sent: Wednesday, June 5, 2024 7:35 PM
> To: ffmpeg-devel at ffmpeg.org <ffmpeg-devel at ffmpeg.org>
> Cc: Mario Hros <k3x-devel at outlook.com>
> Subject: [PATCH] libswscale/x86/yuv2rgb: Add missing EMMS
> 
> Previous rewrite from inline assembly into nasm (commit e934194) missed the required EMMS instruction to bring the x87 FPU back into usable state.
> 
> Signed-off-by: Mario Hros <k3x-devel at outlook.com>
> ---
>  libswscale/x86/yuv_2_rgb.asm | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/libswscale/x86/yuv_2_rgb.asm b/libswscale/x86/yuv_2_rgb.asm
> index e3470fd9ad..7a247797e4 100644
> --- a/libswscale/x86/yuv_2_rgb.asm
> +++ b/libswscale/x86/yuv_2_rgb.asm
> @@ -353,6 +353,7 @@ cglobal %1_420_%2%3, GPR_num, GPR_num, reg_num, parameters
>  add imageq, 8 * depth * time_num
>  add indexq, 4 * time_num
>  js .loop0
> +emms
> 

this feels like its missing a
    %if mmsize == 8

thx

[...]
-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Those who are too smart to engage in politics are punished by being
governed by those who are dumber. -- Plato 
-------------- next part --------------
A non-text attachment was scrubbed...
Name: signature.asc
Type: application/pgp-signature
Size: 195 bytes
Desc: not available
URL: <https://ffmpeg.org/pipermail/ffmpeg-devel/attachments/20240625/d7c0a441/attachment.sig>


More information about the ffmpeg-devel mailing list