libvpx: Add VP9 decoder.

source/libvpx/vp9/decoder/vp9_treereader.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_DECODER_VP9_TREEREADER_H_
+#define VP9_DECODER_VP9_TREEREADER_H_
+
+#include "vp9/common/vp9_treecoder.h"
+
+#include "vp9/decoder/vp9_dboolhuff.h"
+
+typedef BOOL_DECODER vp9_reader;
+
+#define vp9_read decode_bool
+#define vp9_read_literal decode_value
+#define vp9_read_bit(R) vp9_read(R, vp9_prob_half)
+
+/* Intent of tree data structure is to make decoding trivial. */
+
+static int treed_read(vp9_reader *const r, /* !!! must return a 0 or 1 !!! */
+                      vp9_tree t,
+                      const vp9_prob *const p) {
+  register vp9_tree_index i = 0;
+
+  while ((i = t[ i + vp9_read(r, p[i >> 1])]) > 0);
+
+  return -i;
+}
+
+#endif /* tree_reader_h */