[FFmpeg-devel] [PATCH 3/3] h264: new assembly version of get_cabac for x86_64 with PIC

Michael Niedermayer michaelni at gmx.at
Fri Apr 27 21:06:05 CEST 2012

On Fri, Apr 27, 2012 at 03:45:26AM +0200, Roland Scheidegger wrote:
> This adds a hand-optimized assembly version for get_cabac much like the
> existing one, but it works if the table offsets are RIP-relative.
> Compared to the non-RIP-relative version this adds 2 lea instructions
> and it needs one extra register.
> There is a surprisingly large performance improvement over the c version (more
> so than the generated assembly seems to suggest) just in get_cabac, I measured
> roughly 40% faster for get_cabac on a K8. However, overall the difference is
> not that big, I measured roughly 5% on a test clip on a K8 and a Core2.
> Hopefully it still compiles on x86 32bit...
> Now that only one table is used, there's some chance even darwin as compiles
> this (apparently the label arithmetic used previously doesn't work if it
> involves symbols defined in a different file, thanks to Ronald S. Bultje for
> helping me with this).

with the 3 patches applied i get
In file included from libavcodec/cabac_functions.h:36:0,
                 from libavcodec/cabac.c:32:
libavcodec/x86/cabac.h: In function ‘get_cabac_inline_x86’:
libavcodec/x86/cabac.h:169:79: error: macro "BRANCHLESS_GET_CABAC_UPDATE" passed 5 arguments, but takes just 4
libavcodec/x86/cabac.h:167:9: error: expected ‘;’ before string constant
libavcodec/x86/cabac.h:156:14: warning: unused variable ‘tmp’ [-Wunused-variable]

Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Good people do not need laws to tell them to act responsibly, while bad
people will find a way around the laws. -- Plato
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