libvpx: Add VP9 decoder.

source/libvpx/vp9/encoder/vp9_treewriter.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 "vp9/encoder/vp9_treewriter.h"
+
+static void cost(
+  int *const C,
+  vp9_tree T,
+  const vp9_prob *const P,
+  int i,
+  int c
+) {
+  const vp9_prob p = P [i >> 1];
+
+  do {
+    const vp9_tree_index j = T[i];
+    const int d = c + vp9_cost_bit(p, i & 1);
+
+    if (j <= 0)
+      C[-j] = d;
+    else
+      cost(C, T, P, j, d);
+  } while (++i & 1);
+}
+void vp9_cost_tokens(int *c, const vp9_prob *p, vp9_tree t) {
+  cost(c, t, p, 0, 0);
+}
+
+void vp9_cost_tokens_skip(int *c, const vp9_prob *p, vp9_tree t) {
+  cost(c, t, p, 2, 0);
+}