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diff --git a/common/rdft.cpp b/common/rdft.cpp
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+++ b/common/rdft.cpp
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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>
+
+#include "common/rdft.h"
+
+namespace Common {
+
+RDFT::RDFT(int bits, TransformType trans) : _bits(bits), _fft(0) {
+	assert ((_bits >= 4) && (_bits <= 16));
+
+	_inverse        = trans == IDFT_C2R || trans == DFT_C2R;
+	_signConvention = trans == IDFT_R2C || trans == DFT_C2R ? 1 : -1;
+
+	_fft = new FFT(bits - 1, trans == IDFT_C2R || trans == IDFT_R2C);
+
+	int n = 1 << bits;
+
+	_tSin = getSineTable(bits) + (trans == DFT_R2C || trans == DFT_C2R) * (n >> 2);
+	_tCos = getCosineTable(bits);
+}
+
+RDFT::~RDFT() {
+	delete _fft;
+}
+
+void RDFT::calc(float *data) {
+	const int n = 1 << _bits;
+
+	const float k1 = 0.5;
+	const float k2 = 0.5 - _inverse;
+
+	if (!_inverse) {
+		_fft->permute((Complex *) data);
+		_fft->calc   ((Complex *) data);
+	}
+
+	Complex ev, od;
+
+	/* i=0 is a special case because of packing, the DC term is real, so we
+	   are going to throw the N/2 term (also real) in with it. */
+
+	ev.re = data[0];
+
+	data[0] = ev.re + data[1];
+	data[1] = ev.re - data[1];
+
+	int i;
+	for (i = 1; i < (n >> 2); i++) {
+		int i1 = 2 * i;
+		int i2 = n - i1;
+
+		/* Separate even and odd FFTs */
+		ev.re =  k1 * (data[i1    ] + data[i2   ]);
+		od.im = -k2 * (data[i1    ] - data[i2   ]);
+		ev.im =  k1 * (data[i1 + 1] - data[i2 + 1]);
+		od.re =  k2 * (data[i1 + 1] + data[i2 + 1]);
+
+		/* Apply twiddle factors to the odd FFT and add to the even FFT */
+		data[i1    ] =  ev.re + od.re * _tCos[i] - od.im * _tSin[i];
+		data[i1 + 1] =  ev.im + od.im * _tCos[i] + od.re * _tSin[i];
+		data[i2    ] =  ev.re - od.re * _tCos[i] + od.im * _tSin[i];
+		data[i2 + 1] = -ev.im + od.im * _tCos[i] + od.re * _tSin[i];
+	}
+
+	data[2 * i + 1] = _signConvention * data[2 * i + 1];
+
+	if (_inverse) {
+		data[0] *= k1;
+		data[1] *= k1;
+
+		_fft->permute((Complex *) data);
+		_fft->calc   ((Complex *) data);
+	}
+
+}
+
+} // End of namespace Common