[FFmpeg-devel] [PATCH] speedhq: make sure the block index is not negative

Steinar H. Gunderson steinar+ffmpeg at gunderson.no
Tue Jan 31 01:59:16 EET 2017

On Tue, Jan 31, 2017 at 12:49:56AM +0100, Andreas Cadhalpun wrote:
>> How can you get a negative run, which would be required for this to happen?
> Some values in ff_dc_alpha_run_vlc_le.table are negative, e.g.:
>  ff_dc_alpha_run_vlc_le.table[32] = {-1, 0}

This sounds like a strangeness in constructing the table, which shouldn't be
papered over in the inner loop of the decoder. I might be missing something
in how this table is used internally in the bitstream reader, but a code of
32 should just immediately hit 0 in the LSB and be interpreted as run=0.
(There are no invalid codes in this VLC, so nothing like run=-1 should ever

Do you have an actual input where your code makes a difference?

/* Steinar */
Homepage: https://www.sesse.net/

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