[FFmpeg-devel] [PATCH 3/3] lavc: check decoded subtitles encoding.

[Nicolas George]

L'octidi 18 germinal, an CCXXI, Reimar Döffinger a écrit :
> IMHO not for a public API, and preferably not for something that has
> "valid" in its name.
> If it's up to discussion I'd have preferred a more vague name like
> guess_utf8 or such.

Ok.

> Possibly reasonable to add to GET_UTF8 as well - though might be worth
> discussion, also for performance reasons.
> Otherwise I believe this would do it:
> --- a/libavutil/common.h
> +++ b/libavutil/common.h
> @@ -279,6 +279,7 @@ static av_always_inline av_const int av_popcount64_c(uint64_t x)
>  #define GET_UTF8(val, GET_BYTE, ERROR)\
>      val= GET_BYTE;\
>      {\
> +        uint32_t min = 0;\
>          uint32_t top = (val & 128) >> 1;\
>          if ((val & 0xc0) == 0x80)\
>              ERROR\
> @@ -287,9 +288,12 @@ static av_always_inline av_const int av_popcount64_c(uint64_t x)
>              if(tmp>>6)\
>                  ERROR\
>              val= (val<<6) + tmp;\
> +            min = top << 1;\
>              top <<= 5;\
>          }\
>          val &= (top << 1) - 1;\
> +        if (val < min)\
> +            ERROR\
>      }

This seems to cost about 3% performance (281 instead of 271 decicycles for
~33E6 runs). The "val >= 0xFE" test seems to be negligible, OTOH.

I will submit a new pair of patches, keeping the overlong check outside.
Thanks for your help.

Regards,

-- 
  Nicolas George
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