shithub: libvpx

ref: 159cc3b33c718d90a1a3bae87682d1d21d4af480
dir: /vp8/common/treecoder.c/

/*
 *  Copyright (c) 2010 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.
 */

#include <assert.h>
#include <stdio.h>

#include "vp8/common/treecoder.h"

static void tree2tok(struct vp8_token_struct *const p, vp8_tree t, int i, int v,
                     int L) {
  v += v;
  ++L;

  do {
    const vp8_tree_index j = t[i++];

    if (j <= 0) {
      p[-j].value = v;
      p[-j].Len = L;
    } else {
      tree2tok(p, t, j, v, L);
    }
  } while (++v & 1);
}

void vp8_tokens_from_tree(struct vp8_token_struct *p, vp8_tree t) {
  tree2tok(p, t, 0, 0, 0);
}

void vp8_tokens_from_tree_offset(struct vp8_token_struct *p, vp8_tree t,
                                 int offset) {
  tree2tok(p - offset, t, 0, 0, 0);
}

static void branch_counts(int n, /* n = size of alphabet */
                          vp8_token tok[/* n */], vp8_tree tree,
                          unsigned int branch_ct[/* n-1 */][2],
                          const unsigned int num_events[/* n */]) {
  const int tree_len = n - 1;
  int t = 0;

  assert(tree_len);

  do {
    branch_ct[t][0] = branch_ct[t][1] = 0;
  } while (++t < tree_len);

  t = 0;

  do {
    int L = tok[t].Len;
    const int enc = tok[t].value;
    const unsigned int ct = num_events[t];

    vp8_tree_index i = 0;

    do {
      const int b = (enc >> --L) & 1;
      const int j = i >> 1;
      assert(j < tree_len && 0 <= L);

      branch_ct[j][b] += ct;
      i = tree[i + b];
    } while (i > 0);

    assert(!L);
  } while (++t < n);
}

void vp8_tree_probs_from_distribution(int n, /* n = size of alphabet */
                                      vp8_token tok[/* n */], vp8_tree tree,
                                      vp8_prob probs[/* n-1 */],
                                      unsigned int branch_ct[/* n-1 */][2],
                                      const unsigned int num_events[/* n */],
                                      unsigned int Pfac, int rd) {
  const int tree_len = n - 1;
  int t = 0;

  branch_counts(n, tok, tree, branch_ct, num_events);

  do {
    const unsigned int *const c = branch_ct[t];
    const unsigned int tot = c[0] + c[1];

    assert(tot < (1 << 24)); /* no overflow below */

    if (tot) {
      const unsigned int p = ((c[0] * Pfac) + (rd ? tot >> 1 : 0)) / tot;
      probs[t] = p < 256 ? (p ? p : 1) : 255; /* agree w/old version for now */
    } else {
      probs[t] = vp8_prob_half;
    }
  } while (++t < tree_len);
}