[FFmpeg-devel] [PATCH v2] avcodec/cbs_av1: add missing value constrains to point_y_value, point_cb_value and point_cr_value

[Andreas Rheinhardt]

On Thu, Feb 13, 2020 at 4:08 PM James Almer <jamrial at gmail.com> wrote:

> If i is greater than 0, it is a requirement of bitstream conformance that
> point_y_value[ i ] is greater than point_y_value[ i - 1 ].
> If i is greater than 0, it is a requirement of bitstream conformance that
> point_cb_value[ i ] is greater than point_cb_value[ i - 1 ].
> If i is greater than 0, it is a requirement of bitstream conformance that
> point_cr_value[ i ] is greater than point_cr_value[ i - 1 ].
>
> Signed-off-by: James Almer <jamrial at gmail.com>
> ---
> Better version. Now it can't overflow the min value, and will also
> constrain
> the max value to ensure v[i] > v[i-1] is always true.
>

How could the min value overflow at all? After all, the addition v[i - 1] +
1 is performed after promoting v[i - 1] to int. This is then losslessly
converted to uint32_t. So your new version will not detect any more errors
than the old version. It might error out earlier sometimes, but to do so it
always computes the max.
(With the old version it can happen that the min value is bigger than the
max value which leads to the desired error (and an error message that might
be confusing; avoiding this seems to be the only real advantage this new
version has).)

- Andreas