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diff --git a/common/rdft.h b/common/rdft.h
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+/* ScummVM - Graphic Adventure Engine
+ *
+ * ScummVM is the legal property of its developers, whose names
+ * are too numerous to list here. Please refer to the COPYRIGHT
+ * file distributed with this source distribution.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version 2
+ * of the License, or (at your option) any later version.
+
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
+ *
+ */
+
+// Based on eos' (I)RDFT code which is in turn
+// Based upon the (I)RDFT code in FFmpeg
+// Copyright (c) 2009 Alex Converse <alex dot converse at gmail dot com>
+
+#ifndef COMMON_RDFT_H
+#define COMMON_RDFT_H
+
+#include "common/scummsys.h"
+#include "common/math.h"
+#include "common/fft.h"
+
+namespace Common {
+
+/**
+ * (Inverse) Real Discrete Fourier Transform.
+ *
+ * Used in engines:
+ *  - scumm
+ */
+
+class RDFT {
+public:
+	enum TransformType {
+		DFT_R2C,
+		IDFT_C2R,
+		IDFT_R2C,
+		DFT_C2R
+	};
+
+	RDFT(int bits, TransformType trans);
+	~RDFT();
+
+	void calc(float *data);
+
+private:
+	int _bits;
+	int _inverse;
+	int _signConvention;
+
+	const float *_tSin;
+	const float *_tCos;
+
+	FFT *_fft;
+};
+
+} // End of namespace Common
+
+#endif // COMMON_RDFT_H