libvpx: Add VP9 decoder.

source/libvpx/vp9/common/vp9_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 "vpx_config.h"
+
+#if defined(CONFIG_DEBUG) && CONFIG_DEBUG
+#include <assert.h>
+#endif
+#include <stdio.h>
+
+#include "vp9/common/vp9_treecoder.h"
+
+static void tree2tok(
+  struct vp9_token_struct *const p,
+  vp9_tree t,
+  int i,
+  int v,
+  int L
+) {
+  v += v;
+  ++L;
+
+  do {
+    const vp9_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 vp9_tokens_from_tree(struct vp9_token_struct *p, vp9_tree t) {
+  tree2tok(p, t, 0, 0, 0);
+}
+
+void vp9_tokens_from_tree_offset(struct vp9_token_struct *p, vp9_tree t,
+                                 int offset) {
+  tree2tok(p - offset, t, 0, 0, 0);
+}
+
+static void branch_counts(
+  int n,                      /* n = size of alphabet */
+  vp9_token tok               [ /* n */ ],
+  vp9_tree tree,
+  unsigned int branch_ct       [ /* n-1 */ ] [2],
+  const unsigned int num_events[ /* n */ ]
+) {
+  const int tree_len = n - 1;
+  int t = 0;
+
+#if CONFIG_DEBUG
+  assert(tree_len);
+#endif
+
+  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];
+
+    vp9_tree_index i = 0;
+
+    do {
+      const int b = (enc >> --L) & 1;
+      const int j = i >> 1;
+#if CONFIG_DEBUG
+      assert(j < tree_len  &&  0 <= L);
+#endif
+
+      branch_ct [j] [b] += ct;
+      i = tree[ i + b];
+    } while (i > 0);
+
+#if CONFIG_DEBUG
+    assert(!L);
+#endif
+  } while (++t < n);
+
+}
+
+
+void vp9_tree_probs_from_distribution(
+  int n,                      /* n = size of alphabet */
+  vp9_token tok               [ /* n */ ],
+  vp9_tree tree,
+  vp9_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];
+
+#if CONFIG_DEBUG
+    assert(tot < (1 << 24));        /* no overflow below */
+#endif
+
+    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] = vp9_prob_half;
+  } while (++t < tree_len);
+}
+
+vp9_prob vp9_bin_prob_from_distribution(const unsigned int counts[2]) {
+  int tot_count = counts[0] + counts[1];
+  vp9_prob prob;
+  if (tot_count) {
+    prob = (counts[0] * 255 + (tot_count >> 1)) / tot_count;
+    prob += !prob;
+  } else {
+    prob = 128;
+  }
+  return prob;
+}