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113 lines
2.8 KiB
C++
113 lines
2.8 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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* 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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* 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 xoreos' (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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#ifndef COMMON_RDFT_H
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#define COMMON_RDFT_H
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#include "common/scummsys.h"
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#include "common/math.h"
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#include "common/fft.h"
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#include "common/cosinetables.h"
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#include "common/sinetables.h"
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namespace Common {
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/**
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* (Inverse) Real Discrete Fourier Transform.
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*
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* Used in audio:
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* - QDM2
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*
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* Used in engines:
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* - scumm
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*
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*
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* It has four modes:
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*
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* Below, n = 1 << bits
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*
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* (I)DFT_R2C:
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* input:
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* n real floats
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* output:
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* n/2 complex floats (stored as real part followed by imag part).
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*
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* The output represents the first half of the (I)DFT of the input.
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* If F is the complex (I)DFT of the input, then
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* output[0] = F[0] + i * F[n/2] and
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* output[k] = F[k] for k = 1 .. n/2-1.
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* Note that F[0] and F[k] are real since the input is real, and
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* the remaining values of F can be reconstructed from symmetry if desired.
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*
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* (I)DFT_C2R:
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* input:
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* n/2 complex floats
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* output:
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* n real floats
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*
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* The input encodes a complex vector x of length n that has the
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* required symmetry to have a real (I)DFT:
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* x[0] = Re(input[0])
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* x[k] = input[k] for k = 1 .. n/2-1
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* x[n/2] = Im(input[0])
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* x[k] = conj(input[n-k]) for k = n/2+1 .. n-1
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* The output is then the real (I)DFT of x, divided by 2.
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*
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* TODO: Is this division by 2 intentional?
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*/
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class RDFT {
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public:
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enum TransformType {
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DFT_R2C,
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IDFT_C2R,
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IDFT_R2C,
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DFT_C2R
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};
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RDFT(int bits, TransformType trans);
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~RDFT();
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void calc(float *data);
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private:
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int _bits;
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int _inverse;
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int _signConvention;
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SineTable _sin;
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CosineTable _cos;
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const float *_tSin;
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const float *_tCos;
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FFT *_fft;
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};
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} // End of namespace Common
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#endif // COMMON_RDFT_H
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