1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
|
/* 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 3 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, see <http://www.gnu.org/licenses/>.
*
*/
// Based on xoreos' (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 MATH_RDFT_H
#define MATH_RDFT_H
#include "math/cosinetables.h"
#include "math/sinetables.h"
namespace Math {
class FFT;
/**
* @defgroup math_rdft RDFT algorithm
* @ingroup math
*
* @brief API for the Real Discrete Fourier Transform (RDFT) algorithm.
*
* @{
*/
/**
* @brief (Inverse) Real Discrete Fourier Transform.
*
* @details Used in audio:
* - QDM2
*
* Used in engines:
* - scumm
*
*
* It has four modes:
*
* Below, n = 1 << bits
*
* (I)DFT_R2C:
* input:
* n real floats
* output:
* n/2 complex floats (stored as real part followed by imag part).
*
* The output represents the first half of the (I)DFT of the input.
* If F is the complex (I)DFT of the input, then
* output[0] = F[0] + i * F[n/2] and
* output[k] = F[k] for k = 1 .. n/2-1.
* Note that F[0] and F[k] are real since the input is real, and
* the remaining values of F can be reconstructed from symmetry if desired.
*
* (I)DFT_C2R:
* input:
* n/2 complex floats
* output:
* n real floats
*
* The input encodes a complex vector x of length n that has the
* required symmetry to have a real (I)DFT:
* x[0] = Re(input[0])
* x[k] = input[k] for k = 1 .. n/2-1
* x[n/2] = Im(input[0])
* x[k] = conj(input[n-k]) for k = n/2+1 .. n-1
* The output is then the real (I)DFT of x, divided by 2.
*
* TODO: Is this division by 2 intentional?
*/
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;
SineTable _sin;
CosineTable _cos;
const float *_tSin;
const float *_tCos;
FFT *_fft;
};
/** @} */
} // End of namespace Math
#endif // MATH_RDFT_H
|
