libvpx: Add VP9 decoder.

source/libvpx/vp9/encoder/vp9_psnr.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_scale/yv12config.h"
+#include "math.h"
+#include "vp9/common/vp9_systemdependent.h" /* for vp9_clear_system_state() */
+
+#define MAX_PSNR 100
+
+double vp9_mse2psnr(double Samples, double Peak, double Mse) {
+  double psnr;
+
+  if ((double)Mse > 0.0)
+    psnr = 10.0 * log10(Peak * Peak * Samples / Mse);
+  else
+    psnr = MAX_PSNR;      // Limit to prevent / 0
+
+  if (psnr > MAX_PSNR)
+    psnr = MAX_PSNR;
+
+  return psnr;
+}