libvpx: Add VP9 decoder.

source/libvpx/vp9/common/vp9_treecoder.h

+/*
+ *  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.
+ */
+
+
+#ifndef VP9_COMMON_VP9_TREECODER_H_
+#define VP9_COMMON_VP9_TREECODER_H_
+
+typedef unsigned char vp9_prob;
+
+#define vp9_prob_half ( (vp9_prob) 128)
+
+typedef signed char vp9_tree_index;
+struct bool_coder_spec;
+
+typedef struct bool_coder_spec bool_coder_spec;
+typedef struct bool_writer bool_writer;
+typedef struct bool_reader bool_reader;
+
+typedef const bool_coder_spec c_bool_coder_spec;
+typedef const bool_writer c_bool_writer;
+typedef const bool_reader c_bool_reader;
+
+
+
+# define vp9_complement( x) (255 - x)
+
+
+/* We build coding trees compactly in arrays.
+   Each node of the tree is a pair of vp9_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 vp9_tree_index vp9_tree[], *vp9_tree_p;
+
+
+typedef const struct vp9_token_struct {
+  int value;
+  int Len;
+} vp9_token;
+
+/* Construct encoding array from tree. */
+
+void vp9_tokens_from_tree(struct vp9_token_struct *, vp9_tree);
+void vp9_tokens_from_tree_offset(struct vp9_token_struct *, vp9_tree,
+                                 int offset);
+
+
+/* Convert array of token occurrence counts into a table of probabilities
+   for the associated binary encoding tree.  Also writes count of branches
+   taken for each node on the tree; this facilitiates decisions as to
+   probability updates. */
+
+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 Pfactor,
+  int Round
+);
+
+static __inline int clip_prob(int p) {
+  if (p > 255)
+    return 255;
+  else if (p < 1)
+    return 1;
+  return p;
+}
+
+vp9_prob vp9_bin_prob_from_distribution(const unsigned int counts[2]);
+
+#endif