/src/libvpx/vpx_dsp/prob.h

Source
/*
 *  Copyright (c) 2013 The WebM project authors. All Rights Reserved.
 *
 *  Use of this source code is governed by a BSD-style license
 *  that can be found in the LICENSE file in the root of the source
 *  tree. An additional intellectual property rights grant can be found
 *  in the file PATENTS.  All contributing project authors may
 *  be found in the AUTHORS file in the root of the source tree.
 */

#ifndef VPX_VPX_DSP_PROB_H_
#define VPX_VPX_DSP_PROB_H_

#include <assert.h>

#include "./vpx_config.h"
#include "./vpx_dsp_common.h"

#include "vpx_ports/mem.h"

#ifdef __cplusplus
extern "C" {
#endif

typedef uint8_t vpx_prob;

#define MAX_PROB 255

#define vpx_prob_half ((vpx_prob)128)

typedef int8_t vpx_tree_index;

#define TREE_SIZE(leaf_count) (2 * (leaf_count) - 2)

#define vpx_complement(x) (255 - (x))

#define MODE_MV_COUNT_SAT 20

/* We build coding trees compactly in arrays.
   Each node of the tree is a pair of vpx_tree_indices.
   Array index often references a corresponding probability table.
   Index <= 0 means done encoding/decoding and value = -Index,
   Index > 0 means need another bit, specification at index.
   Nonnegative indices are always even;  processing begins at node 0. */

typedef const vpx_tree_index vpx_tree[];

static INLINE vpx_prob get_prob(unsigned int num, unsigned int den) {
  assert(den != 0);
  {
    const int p = (int)(((uint64_t)num * 256 + (den >> 1)) / den);
    // (p > 255) ? 255 : (p < 1) ? 1 : p;
    const int clipped_prob = p | ((255 - p) >> 23) | (p == 0);
    return (vpx_prob)clipped_prob;
  }
}

static INLINE vpx_prob get_binary_prob(unsigned int n0, unsigned int n1) {
  const unsigned int den = n0 + n1;
  if (den == 0) return 128u;
  return get_prob(n0, den);
}

/* This function assumes prob1 and prob2 are already within [1,255] range. */
static INLINE vpx_prob weighted_prob(int prob1, int prob2, int factor) {
  return ROUND_POWER_OF_TWO(prob1 * (256 - factor) + prob2 * factor, 8);
}

static INLINE vpx_prob merge_probs(vpx_prob pre_prob, const unsigned int ct[2],
                                   unsigned int count_sat,
                                   unsigned int max_update_factor) {
  const vpx_prob prob = get_binary_prob(ct[0], ct[1]);
  const unsigned int count = VPXMIN(ct[0] + ct[1], count_sat);
  const unsigned int factor = max_update_factor * count / count_sat;
  return weighted_prob(pre_prob, prob, factor);
}

// MODE_MV_MAX_UPDATE_FACTOR (128) * count / MODE_MV_COUNT_SAT;
static const int count_to_update_factor[MODE_MV_COUNT_SAT + 1] = {
  0,  6,  12, 19, 25, 32,  38,  44,  51,  57, 64,
  70, 76, 83, 89, 96, 102, 108, 115, 121, 128
};

static INLINE vpx_prob mode_mv_merge_probs(vpx_prob pre_prob,
                                           const unsigned int ct[2]) {
  const unsigned int den = ct[0] + ct[1];
  if (den == 0) {
    return pre_prob;
  } else {
    const unsigned int count = VPXMIN(den, MODE_MV_COUNT_SAT);
    const unsigned int factor = count_to_update_factor[count];
    const vpx_prob prob = get_prob(ct[0], den);
    return weighted_prob(pre_prob, prob, factor);
  }
}

void vpx_tree_merge_probs(const vpx_tree_index *tree, const vpx_prob *pre_probs,
                          const unsigned int *counts, vpx_prob *probs);

DECLARE_ALIGNED(16, extern const uint8_t, vpx_norm[256]);

#ifdef __cplusplus
}  // extern "C"
#endif

#endif  // VPX_VPX_DSP_PROB_H_

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Created: 2025-08-28 07:12