commit 29071a418e1a12fb2f614f962c24f1417153d7fc
author Alexander Voronov <avoronov@graphics.cs.msu.ru> Tue Sep 09 14:56:00 2014 +0400
committer Alexander Voronov <avoronov@graphics.cs.msu.ru> Mon Sep 15 17:50:20 2014 +0400
tree 5e4397233cd86f562f35369b2380a53bae8b2bab
parent c731d6a4f19eea861ceb2ff31399420b2452eb74

Fix invalid memory access on 2x downscale.

The issue was discovered on bitstream with 2x vertical downscale. For
zero MVs, y_pad is set to 1 only when vertical convolution is
required. The original code assumes that for y_step_q4 == 32 we don't
perform vertical convolution. But vp9_setup_scale_factors_for_frame()
sets convolve functions so that when x_step and y_step are both not
equal to 16, convolve in both directions is performed. And convolve()
unconditionally subtracts one stride from source pointer when calls
convolve_horiz(). This leads to invalid memory access.

Change-Id: I882dfa6081a58e172b5ffa55842bfcd6727f10bf