tree 8bf5d1c2dfa79ca0b33aaa6cb1baef3e9fe758c2
parent e11f27c52212b76b20bbaf508c96a23bddb381a0
author Wan-Teh Chang <wtc@google.com> 1562021674 -0700
committer Wan-Teh Chang <wtc@google.com> 1562345267 +0000

Index skip_contexts with top/left, not min/max.

If we index the skip_contexts table with min and max, the matrix is
actually upper triangular because only the main diagonal and the entries
above the main diagonal are used (min <= max). If we index skip_contexts
with top and left instead, then the matrix is symmetric and no entries
are wasted. Also, we don't need to calculate min and max.

Background info: The code modified in this CL was added in a series of
three CLs:
- https://aomedia-review.googlesource.com/c/aom/+/39524. (This CL was
  reverted because of a bug in the dc_sign_contexts table.)
- https://aomedia-review.googlesource.com/c/aom/+/39902. (Fixed the bug
  in the dc_sign_contexts table.)
- https://aomedia-review.googlesource.com/c/aom/+/53423. (Edited the
  comment that describes how the table was generated.)

It is not clear by reading the code review comments of these three CLs
why the skip_contexts table was not upper triagonal or symmetric.

Change-Id: Iaa0355991620f2cae2f0666b0a3901a21eb032aa