[FFmpeg-devel] [PATCH 24/25] avcodec/fraps: Use unchecked bitstream reader

[Paul B Mahol]

On Sat, Sep 26, 2020 at 12:28:03PM +0200, Andreas Rheinhardt wrote:
> The fraps decoder already checked for overreads manually (and errored
> out in this scenario), yet it still enabled implicit checks, leading to
> worse performance and more code size.
> 
> This commit disables the implicit bitstream reader checks. For the
> sample [1] this improves performance from 195105896 to 155851561
> decicycles for Clang 10 and from 222801887 to 168270467 decicycles when
> compiled with GCC 9.3. These values are the average of 10 runs each
> looping ten times over the input.
> 
> [1]: samples.ffmpeg.org/ffmpeg-bugs/trac/ticket2593/fraps_flv1_decoding_errors.avi

probably ok

> 
> Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt at gmail.com>
> ---
>  libavcodec/fraps.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/libavcodec/fraps.c b/libavcodec/fraps.c
> index 7a7673f73f..00fd63ffec 100644
> --- a/libavcodec/fraps.c
> +++ b/libavcodec/fraps.c
> @@ -31,6 +31,7 @@
>   * Version 2 files support by Konstantin Shishkov
>   */
>  
> +#define UNCHECKED_BITSTREAM_READER 1
>  #include "avcodec.h"
>  #include "get_bits.h"
>  #include "huffman.h"
> -- 
> 2.25.1
> 
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