This patch added two features to improve entropy coding efficiency
for coefficient tokens.
1. Choose 1 of 4 default probability tables based on q-index for
key-frames.
It is ported from nextgen branch:
https://chromium-review.googlesource.com/#/c/280586/
2. Do backward update after each superblock (64X64) row using
subframe token counts.
Coding gain: 0.1% on lowres; 0.42% on midres; 0.36% on hdres.
Much larger gain for key-frames: 2.6%, 2.3%, 1.7%.
Design doc: go/huisu-entropy
Change-Id: Ia3b6a615636be09247d70e4c520405637561532b
Make the RANS implementation operate on cumulative distribution
functions rather than individual probability distribution functions.
CDFs have shown themselves more flexible to work with.
Reduces decoding memory usage from scaling O(num_distributions *
symbol_resolution) to O(num_distributions).
No bitstream change. This is an purely implementation change.
Change-Id: I4e18d3a0a3d37a36a61487c3d778f9d088b0b374
Don't initialize first pass costs for a number of symbols where first
pass probabilities aren't initialized.
As a side effect, an illegal read in the ANS experiment is fixed.
https://bugs.chromium.org/p/webm/issues/detail?id=1089
Change-Id: I97438c357bd88f52f5a15c697031cf0c3cc8f510
The old workaround "p = 0 ? 0 : p -1" is misleading.
?: happens before =
assigning back to p truncates to one byte.
Therefore it is equivalent to (p - 1) & 0xFF, but the check just exists
to work around a first pass bug, so let's make the work around more
clear.
https://bugs.chromium.org/p/webm/issues/detail?id=1089
Change-Id: I587c44dd61c1f3767543c0126376f881889935af
This reverts commit 7f56cb2978.
It causes uninitialized reads in the first pass setting up later cost tables.
Change-Id: I2df498df3f5c03eff359f79edf045aed0c618dc9
The old workaround "p = 0 ? 0 : p -1" is misleading.
?: happens before =
assigning back to p truncates to one byte.
Therefore it is equivalent to (p - 1) & 0xFF, but the check just exists
to work around a first pass bug, so let's make the work around more
clear.
https://code.google.com/p/webm/issues/detail?id=1089
Change-Id: Ia6dcc8922e1acbac0eeca23a4d564a355c489572
