Add some external dependencies.

extern/EtcLib/Etc/EtcMath.h

@@ -0,0 +1,40 @@
+/*
+ * Copyright 2015 The Etc2Comp Authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *  http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#pragma once
+
+#include <math.h>
+
+namespace Etc
+{
+
+	// ----------------------------------------------------------------------------------------------------
+	// return true if vertical line
+	bool Regression(float a_afX[], float a_afY[], unsigned int a_Points,
+					float *a_fSlope, float *a_fOffset);
+
+	inline float ConvertMSEToPSNR(float a_fMSE)
+	{
+		if (a_fMSE == 0.0f)
+		{
+			return INFINITY;
+		}
+
+		return 10.0f * log10f(1.0f / a_fMSE);
+	}
+
+
+}