## ffmpeg / libavcodec / rdft.c @ 2881c831

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1 | 68602540 | Alex Converse | ```
/*
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2 | ```
* (I)RDFT transforms
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3 | ```
* Copyright (c) 2009 Alex Converse <alex dot converse at gmail dot com>
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4 | ```
*
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5 | ```
* This file is part of FFmpeg.
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6 | ```
*
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7 | ```
* FFmpeg is free software; you can redistribute it and/or
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8 | ```
* modify it under the terms of the GNU Lesser General Public
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9 | ```
* License as published by the Free Software Foundation; either
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10 | ```
* version 2.1 of the License, or (at your option) any later version.
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11 | ```
*
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12 | ```
* FFmpeg is distributed in the hope that it will be useful,
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13 | ```
* but WITHOUT ANY WARRANTY; without even the implied warranty of
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14 | ```
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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15 | ```
* Lesser General Public License for more details.
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16 | ```
*
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17 | ```
* You should have received a copy of the GNU Lesser General Public
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18 | ```
* License along with FFmpeg; if not, write to the Free Software
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19 | ```
* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
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20 | ```
*/
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21 | 2ed6f399 | Måns Rullgård | #include <stdlib.h> |

22 | 68602540 | Alex Converse | #include <math.h> |

23 | 1429224b | Måns Rullgård | #include "libavutil/mathematics.h" |

24 | #include "fft.h" |
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25 | 68602540 | Alex Converse | |

26 | ```
/**
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27 | bad5537e | Diego Biurrun | ```
* @file libavcodec/rdft.c
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28 | 68602540 | Alex Converse | ```
* (Inverse) Real Discrete Fourier Transforms.
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29 | ```
*/
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30 | |||

31 | ```
/* sin(2*pi*x/n) for 0<=x<n/4, followed by n/2<=x<3n/4 */
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32 | 75df2edb | Reimar Döffinger | ```
#if !CONFIG_HARDCODED_TABLES
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33 | 4ee726b6 | Reimar Döffinger | ```
SINTABLE(16);
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34 | ```
SINTABLE(32);
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35 | ```
SINTABLE(64);
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36 | ```
SINTABLE(128);
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37 | ```
SINTABLE(256);
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38 | ```
SINTABLE(512);
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39 | ```
SINTABLE(1024);
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40 | ```
SINTABLE(2048);
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41 | ```
SINTABLE(4096);
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42 | ```
SINTABLE(8192);
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43 | ```
SINTABLE(16384);
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44 | ```
SINTABLE(32768);
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45 | ```
SINTABLE(65536);
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46 | 75df2edb | Reimar Döffinger | ```
#endif
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47 | ```
SINTABLE_CONST FFTSample * const ff_sin_tabs[] = {
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48 | 22321774 | Reimar Döffinger | NULL, NULL, NULL, NULL, |

49 | 68602540 | Alex Converse | ff_sin_16, ff_sin_32, ff_sin_64, ff_sin_128, ff_sin_256, ff_sin_512, ff_sin_1024, |

50 | ff_sin_2048, ff_sin_4096, ff_sin_8192, ff_sin_16384, ff_sin_32768, ff_sin_65536, |
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51 | }; |
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52 | |||

53 | 2881c831 | Måns Rullgård | static void ff_rdft_calc_c(RDFTContext* s, FFTSample* data); |

54 | |||

55 | 68602540 | Alex Converse | av_cold int ff_rdft_init(RDFTContext *s, int nbits, enum RDFTransformType trans) |

56 | { |
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57 | int n = 1 << nbits; |
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58 | ```
int i;
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59 | 41ea18fb | Måns Rullgård | const double theta = (trans == DFT_R2C || trans == DFT_C2R ? -1 : 1)*2*M_PI/n; |

60 | 68602540 | Alex Converse | |

61 | s->nbits = nbits; |
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62 | 41ea18fb | Måns Rullgård | s->inverse = trans == IDFT_C2R || trans == DFT_C2R; |

63 | s->sign_convention = trans == IDFT_R2C || trans == DFT_C2R ? 1 : -1; |
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64 | 68602540 | Alex Converse | |

65 | if (nbits < 4 || nbits > 16) |
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66 | return -1; |
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67 | |||

68 | 41ea18fb | Måns Rullgård | if (ff_fft_init(&s->fft, nbits-1, trans == IDFT_C2R || trans == IDFT_R2C) < 0) |

69 | 68602540 | Alex Converse | return -1; |

70 | |||

71 | 1ffc6e83 | Reimar Döffinger | ff_init_ff_cos_tabs(nbits); |

72 | 22321774 | Reimar Döffinger | s->tcos = ff_cos_tabs[nbits]; |

73 | 41ea18fb | Måns Rullgård | ```
s->tsin = ff_sin_tabs[nbits]+(trans == DFT_R2C || trans == DFT_C2R)*(n>>2);
``` |

74 | 75df2edb | Reimar Döffinger | ```
#if !CONFIG_HARDCODED_TABLES
``` |

75 | 68602540 | Alex Converse | for (i = 0; i < (n>>2); i++) { |

76 | s->tsin[i] = sin(i*theta); |
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77 | } |
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78 | 75df2edb | Reimar Döffinger | ```
#endif
``` |

79 | 2881c831 | Måns Rullgård | s->rdft_calc = ff_rdft_calc_c; |

80 | 68602540 | Alex Converse | return 0; |

81 | } |
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82 | |||

83 | ```
/** Map one real FFT into two parallel real even and odd FFTs. Then interleave
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84 | ```
* the two real FFTs into one complex FFT. Unmangle the results.
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85 | ```
* ref: http://www.engineeringproductivitytools.com/stuff/T0001/PT10.HTM
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86 | ```
*/
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87 | da0ac0ee | Måns Rullgård | static void ff_rdft_calc_c(RDFTContext* s, FFTSample* data) |

88 | 68602540 | Alex Converse | { |

89 | ```
int i, i1, i2;
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90 | FFTComplex ev, od; |
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91 | const int n = 1 << s->nbits; |
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92 | const float k1 = 0.5; |
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93 | const float k2 = 0.5 - s->inverse; |
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94 | ```
const FFTSample *tcos = s->tcos;
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95 | ```
const FFTSample *tsin = s->tsin;
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96 | |||

97 | ```
if (!s->inverse) {
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98 | ff_fft_permute(&s->fft, (FFTComplex*)data); |
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99 | ff_fft_calc(&s->fft, (FFTComplex*)data); |
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100 | } |
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101 | ```
/* i=0 is a special case because of packing, the DC term is real, so we
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102 | ```
are going to throw the N/2 term (also real) in with it. */
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103 | ```
ev.re = data[0];
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104 | data[0] = ev.re+data[1]; |
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105 | data[1] = ev.re-data[1]; |
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106 | for (i = 1; i < (n>>2); i++) { |
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107 | ```
i1 = 2*i;
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108 | i2 = n-i1; |
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109 | ```
/* Separate even and odd FFTs */
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110 | ev.re = k1*(data[i1 ]+data[i2 ]); |
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111 | od.im = -k2*(data[i1 ]-data[i2 ]); |
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112 | ev.im = k1*(data[i1+1]-data[i2+1]); |
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113 | od.re = k2*(data[i1+1]+data[i2+1]); |
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114 | ```
/* Apply twiddle factors to the odd FFT and add to the even FFT */
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115 | data[i1 ] = ev.re + od.re*tcos[i] - od.im*tsin[i]; |
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116 | ```
data[i1+1] = ev.im + od.im*tcos[i] + od.re*tsin[i];
``` |
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117 | data[i2 ] = ev.re - od.re*tcos[i] + od.im*tsin[i]; |
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118 | ```
data[i2+1] = -ev.im + od.im*tcos[i] + od.re*tsin[i];
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119 | } |
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120 | data[2*i+1]=s->sign_convention*data[2*i+1]; |
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121 | ```
if (s->inverse) {
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122 | ```
data[0] *= k1;
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123 | ```
data[1] *= k1;
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124 | ff_fft_permute(&s->fft, (FFTComplex*)data); |
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125 | ff_fft_calc(&s->fft, (FFTComplex*)data); |
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126 | } |
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127 | } |
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128 | |||

129 | ```
av_cold void ff_rdft_end(RDFTContext *s)
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130 | { |
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131 | ff_fft_end(&s->fft); |
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132 | } |