bd84685f78
The previous implementation visited each node in the tree multiple times because it used each symbol's encoding to revisit the branches taken and increment its count. Instead, we can traverse the tree depth first and calculate the probabilities and branch counts as we walk back up. The complexity goes from somewhere between O(nlogn) and O(n^2) (depending on how balanced the tree is) to O(n). Only tested one clip (256kbps, CIF), saw 13% decoding perf improvement. Note that this optimization should port trivially to VP8 as well. In VP8, the decoder doesn't use this function, but it does routinely show up on the profile for realtime encoding. Change-Id: I4f2848e4f41dc9a7694f73f3e75034bce08d1b12
83 lines
2.8 KiB
C
83 lines
2.8 KiB
C
/*
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* Copyright (c) 2010 The WebM project authors. All Rights Reserved.
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*
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* Use of this source code is governed by a BSD-style license
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* that can be found in the LICENSE file in the root of the source
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* tree. An additional intellectual property rights grant can be found
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* in the file PATENTS. All contributing project authors may
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* be found in the AUTHORS file in the root of the source tree.
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*/
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#ifndef VP9_COMMON_VP9_TREECODER_H_
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#define VP9_COMMON_VP9_TREECODER_H_
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#include "./vpx_config.h"
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#include "vpx/vpx_integer.h"
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typedef uint8_t vp9_prob;
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#define vp9_prob_half ((vp9_prob) 128)
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typedef int8_t vp9_tree_index;
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#define vp9_complement(x) (255 - x)
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/* We build coding trees compactly in arrays.
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Each node of the tree is a pair of vp9_tree_indices.
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Array index often references a corresponding probability table.
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Index <= 0 means done encoding/decoding and value = -Index,
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Index > 0 means need another bit, specification at index.
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Nonnegative indices are always even; processing begins at node 0. */
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typedef const vp9_tree_index vp9_tree[], *vp9_tree_p;
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typedef const struct vp9_token_struct {
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int value;
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int Len;
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} vp9_token;
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/* Construct encoding array from tree. */
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void vp9_tokens_from_tree(struct vp9_token_struct *, vp9_tree);
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void vp9_tokens_from_tree_offset(struct vp9_token_struct *, vp9_tree,
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int offset);
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/* Convert array of token occurrence counts into a table of probabilities
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for the associated binary encoding tree. Also writes count of branches
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taken for each node on the tree; this facilitiates decisions as to
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probability updates. */
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void vp9_tree_probs_from_distribution(vp9_tree tree,
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vp9_prob probs[ /* n - 1 */ ],
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unsigned int branch_ct[ /* n - 1 */ ][2],
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const unsigned int num_events[ /* n */ ],
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unsigned int tok0_offset);
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static INLINE vp9_prob clip_prob(int p) {
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return (p > 255) ? 255u : (p < 1) ? 1u : p;
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}
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// int64 is not needed for normal frame level calculations.
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// However when outputing entropy stats accumulated over many frames
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// or even clips we can overflow int math.
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#ifdef ENTROPY_STATS
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static INLINE vp9_prob get_prob(int num, int den) {
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return (den == 0) ? 128u : clip_prob(((int64_t)num * 256 + (den >> 1)) / den);
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}
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#else
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static INLINE vp9_prob get_prob(int num, int den) {
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return (den == 0) ? 128u : clip_prob((num * 256 + (den >> 1)) / den);
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}
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#endif
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static INLINE vp9_prob get_binary_prob(int n0, int n1) {
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return get_prob(n0, n0 + n1);
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}
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/* this function assumes prob1 and prob2 are already within [1,255] range */
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static INLINE vp9_prob weighted_prob(int prob1, int prob2, int factor) {
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return (prob1 * (256 - factor) + prob2 * factor + 128) >> 8;
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}
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#endif // VP9_COMMON_VP9_TREECODER_H_
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