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101 lines
2.9 KiB
C++
101 lines
2.9 KiB
C++
/* ScummVM - Graphic Adventure Engine
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*
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* ScummVM is the legal property of its developers, whose names
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* are too numerous to list here. Please refer to the COPYRIGHT
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* file distributed with this source distribution.
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public License
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* as published by the Free Software Foundation; either version 2
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* of the License, or (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, write to the Free Software
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* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
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*
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*/
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// Based on eos' (I)RDFT code which is in turn
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// Based upon the (I)RDFT code in FFmpeg
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// Copyright (c) 2009 Alex Converse <alex dot converse at gmail dot com>
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#include "common/rdft.h"
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namespace Common {
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RDFT::RDFT(int bits, TransformType trans) : _bits(bits), _sin(bits), _cos(bits), _fft(0) {
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assert ((_bits >= 4) && (_bits <= 16));
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_inverse = trans == IDFT_C2R || trans == DFT_C2R;
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_signConvention = trans == IDFT_R2C || trans == DFT_C2R ? 1 : -1;
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_fft = new FFT(bits - 1, trans == IDFT_C2R || trans == IDFT_R2C);
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int n = 1 << bits;
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_tSin = _sin.getTable() + (trans == DFT_R2C || trans == DFT_C2R) * (n >> 2);
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_tCos = _cos.getTable();
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}
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RDFT::~RDFT() {
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delete _fft;
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}
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void RDFT::calc(float *data) {
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const int n = 1 << _bits;
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const float k1 = 0.5;
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const float k2 = 0.5 - _inverse;
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if (!_inverse) {
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_fft->permute((Complex *) data);
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_fft->calc ((Complex *) data);
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}
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Complex ev, od;
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/* i=0 is a special case because of packing, the DC term is real, so we
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are going to throw the N/2 term (also real) in with it. */
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ev.re = data[0];
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data[0] = ev.re + data[1];
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data[1] = ev.re - data[1];
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int i;
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for (i = 1; i < (n >> 2); i++) {
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int i1 = 2 * i;
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int i2 = n - i1;
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/* Separate even and odd FFTs */
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ev.re = k1 * (data[i1 ] + data[i2 ]);
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od.im = -k2 * (data[i1 ] - data[i2 ]);
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ev.im = k1 * (data[i1 + 1] - data[i2 + 1]);
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od.re = k2 * (data[i1 + 1] + data[i2 + 1]);
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/* Apply twiddle factors to the odd FFT and add to the even FFT */
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data[i1 ] = ev.re + od.re * _tCos[i] - od.im * _tSin[i];
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data[i1 + 1] = ev.im + od.im * _tCos[i] + od.re * _tSin[i];
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data[i2 ] = ev.re - od.re * _tCos[i] + od.im * _tSin[i];
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data[i2 + 1] = -ev.im + od.im * _tCos[i] + od.re * _tSin[i];
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}
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data[2 * i + 1] = _signConvention * data[2 * i + 1];
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if (_inverse) {
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data[0] *= k1;
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data[1] *= k1;
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_fft->permute((Complex *) data);
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_fft->calc ((Complex *) data);
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}
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}
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} // End of namespace Common
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