Statistics
| Branch: | Revision:

ffmpeg / libavcodec / rdft.c @ 2912e87a

History | View | Annotate | Download (4.12 KB)

1
/*
2
 * (I)RDFT transforms
3
 * Copyright (c) 2009 Alex Converse <alex dot converse at gmail dot com>
4
 *
5
 * This file is part of Libav.
6
 *
7
 * Libav is free software; you can redistribute it and/or
8
 * modify it under the terms of the GNU Lesser General Public
9
 * License as published by the Free Software Foundation; either
10
 * version 2.1 of the License, or (at your option) any later version.
11
 *
12
 * Libav is distributed in the hope that it will be useful,
13
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
14
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
15
 * Lesser General Public License for more details.
16
 *
17
 * You should have received a copy of the GNU Lesser General Public
18
 * License along with Libav; if not, write to the Free Software
19
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
20
 */
21
#include <stdlib.h>
22
#include <math.h>
23
#include "libavutil/mathematics.h"
24
#include "fft.h"
25

    
26
/**
27
 * @file
28
 * (Inverse) Real Discrete Fourier Transforms.
29
 */
30

    
31
/* sin(2*pi*x/n) for 0<=x<n/4, followed by n/2<=x<3n/4 */
32
#if !CONFIG_HARDCODED_TABLES
33
SINTABLE(16);
34
SINTABLE(32);
35
SINTABLE(64);
36
SINTABLE(128);
37
SINTABLE(256);
38
SINTABLE(512);
39
SINTABLE(1024);
40
SINTABLE(2048);
41
SINTABLE(4096);
42
SINTABLE(8192);
43
SINTABLE(16384);
44
SINTABLE(32768);
45
SINTABLE(65536);
46
#endif
47
static SINTABLE_CONST FFTSample * const ff_sin_tabs[] = {
48
    NULL, NULL, NULL, NULL,
49
    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,
51
};
52

    
53
/** Map one real FFT into two parallel real even and odd FFTs. Then interleave
54
 * the two real FFTs into one complex FFT. Unmangle the results.
55
 * ref: http://www.engineeringproductivitytools.com/stuff/T0001/PT10.HTM
56
 */
57
static void ff_rdft_calc_c(RDFTContext* s, FFTSample* data)
58
{
59
    int i, i1, i2;
60
    FFTComplex ev, od;
61
    const int n = 1 << s->nbits;
62
    const float k1 = 0.5;
63
    const float k2 = 0.5 - s->inverse;
64
    const FFTSample *tcos = s->tcos;
65
    const FFTSample *tsin = s->tsin;
66

    
67
    if (!s->inverse) {
68
        ff_fft_permute(&s->fft, (FFTComplex*)data);
69
        ff_fft_calc(&s->fft, (FFTComplex*)data);
70
    }
71
    /* i=0 is a special case because of packing, the DC term is real, so we
72
       are going to throw the N/2 term (also real) in with it. */
73
    ev.re = data[0];
74
    data[0] = ev.re+data[1];
75
    data[1] = ev.re-data[1];
76
    for (i = 1; i < (n>>2); i++) {
77
        i1 = 2*i;
78
        i2 = n-i1;
79
        /* Separate even and odd FFTs */
80
        ev.re =  k1*(data[i1  ]+data[i2  ]);
81
        od.im = -k2*(data[i1  ]-data[i2  ]);
82
        ev.im =  k1*(data[i1+1]-data[i2+1]);
83
        od.re =  k2*(data[i1+1]+data[i2+1]);
84
        /* Apply twiddle factors to the odd FFT and add to the even FFT */
85
        data[i1  ] =  ev.re + od.re*tcos[i] - od.im*tsin[i];
86
        data[i1+1] =  ev.im + od.im*tcos[i] + od.re*tsin[i];
87
        data[i2  ] =  ev.re - od.re*tcos[i] + od.im*tsin[i];
88
        data[i2+1] = -ev.im + od.im*tcos[i] + od.re*tsin[i];
89
    }
90
    data[2*i+1]=s->sign_convention*data[2*i+1];
91
    if (s->inverse) {
92
        data[0] *= k1;
93
        data[1] *= k1;
94
        ff_fft_permute(&s->fft, (FFTComplex*)data);
95
        ff_fft_calc(&s->fft, (FFTComplex*)data);
96
    }
97
}
98

    
99
av_cold int ff_rdft_init(RDFTContext *s, int nbits, enum RDFTransformType trans)
100
{
101
    int n = 1 << nbits;
102
    int i;
103
    const double theta = (trans == DFT_R2C || trans == DFT_C2R ? -1 : 1)*2*M_PI/n;
104

    
105
    s->nbits           = nbits;
106
    s->inverse         = trans == IDFT_C2R || trans == DFT_C2R;
107
    s->sign_convention = trans == IDFT_R2C || trans == DFT_C2R ? 1 : -1;
108

    
109
    if (nbits < 4 || nbits > 16)
110
        return -1;
111

    
112
    if (ff_fft_init(&s->fft, nbits-1, trans == IDFT_C2R || trans == IDFT_R2C) < 0)
113
        return -1;
114

    
115
    ff_init_ff_cos_tabs(nbits);
116
    s->tcos = ff_cos_tabs[nbits];
117
    s->tsin = ff_sin_tabs[nbits]+(trans == DFT_R2C || trans == DFT_C2R)*(n>>2);
118
#if !CONFIG_HARDCODED_TABLES
119
    for (i = 0; i < (n>>2); i++) {
120
        s->tsin[i] = sin(i*theta);
121
    }
122
#endif
123
    s->rdft_calc   = ff_rdft_calc_c;
124

    
125
    if (ARCH_ARM) ff_rdft_init_arm(s);
126

    
127
    return 0;
128
}
129

    
130
av_cold void ff_rdft_end(RDFTContext *s)
131
{
132
    ff_fft_end(&s->fft);
133
}