f37263b7c2b12dbeb2ec0346b44226e5bd90ffc7
[libav.git] / libavcodec / rdft.c
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 FFmpeg.
6 *
7 * FFmpeg 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 * FFmpeg 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 FFmpeg; 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 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 }