3 * Copyright (c) 2009 Alex Converse <alex dot converse at gmail dot com>
5 * This file is part of FFmpeg.
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.
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.
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
25 * @file libavcodec/rdft.c
26 * (Inverse) Real Discrete Fourier Transforms.
29 /* sin(2*pi*x/n) for 0<=x<n/4, followed by n/2<=x<3n/4 */
30 #if !CONFIG_HARDCODED_TABLES
45 SINTABLE_CONST FFTSample * const ff_sin_tabs[] = {
46 NULL, NULL, NULL, NULL,
47 ff_sin_16, ff_sin_32, ff_sin_64, ff_sin_128, ff_sin_256, ff_sin_512, ff_sin_1024,
48 ff_sin_2048, ff_sin_4096, ff_sin_8192, ff_sin_16384, ff_sin_32768, ff_sin_65536,
51 av_cold int ff_rdft_init(RDFTContext *s, int nbits, enum RDFTransformType trans)
55 const double theta = (trans == RDFT || trans == IRIDFT ? -1 : 1)*2*M_PI/n;
58 s->inverse = trans == IRDFT || trans == IRIDFT;
59 s->sign_convention = trans == RIDFT || trans == IRIDFT ? 1 : -1;
61 if (nbits < 4 || nbits > 16)
64 if (ff_fft_init(&s->fft, nbits-1, trans == IRDFT || trans == RIDFT) < 0)
67 ff_init_ff_cos_tabs(nbits);
68 s->tcos = ff_cos_tabs[nbits];
69 s->tsin = ff_sin_tabs[nbits]+(trans == RDFT || trans == IRIDFT)*(n>>2);
70 #if !CONFIG_HARDCODED_TABLES
71 for (i = 0; i < (n>>2); i++) {
72 s->tsin[i] = sin(i*theta);
78 /** Map one real FFT into two parallel real even and odd FFTs. Then interleave
79 * the two real FFTs into one complex FFT. Unmangle the results.
80 * ref: http://www.engineeringproductivitytools.com/stuff/T0001/PT10.HTM
82 void ff_rdft_calc_c(RDFTContext* s, FFTSample* data)
86 const int n = 1 << s->nbits;
88 const float k2 = 0.5 - s->inverse;
89 const FFTSample *tcos = s->tcos;
90 const FFTSample *tsin = s->tsin;
93 ff_fft_permute(&s->fft, (FFTComplex*)data);
94 ff_fft_calc(&s->fft, (FFTComplex*)data);
96 /* i=0 is a special case because of packing, the DC term is real, so we
97 are going to throw the N/2 term (also real) in with it. */
99 data[0] = ev.re+data[1];
100 data[1] = ev.re-data[1];
101 for (i = 1; i < (n>>2); i++) {
104 /* Separate even and odd FFTs */
105 ev.re = k1*(data[i1 ]+data[i2 ]);
106 od.im = -k2*(data[i1 ]-data[i2 ]);
107 ev.im = k1*(data[i1+1]-data[i2+1]);
108 od.re = k2*(data[i1+1]+data[i2+1]);
109 /* Apply twiddle factors to the odd FFT and add to the even FFT */
110 data[i1 ] = ev.re + od.re*tcos[i] - od.im*tsin[i];
111 data[i1+1] = ev.im + od.im*tcos[i] + od.re*tsin[i];
112 data[i2 ] = ev.re - od.re*tcos[i] + od.im*tsin[i];
113 data[i2+1] = -ev.im + od.im*tcos[i] + od.re*tsin[i];
115 data[2*i+1]=s->sign_convention*data[2*i+1];
119 ff_fft_permute(&s->fft, (FFTComplex*)data);
120 ff_fft_calc(&s->fft, (FFTComplex*)data);
124 void ff_rdft_calc(RDFTContext *s, FFTSample *data)
126 ff_rdft_calc_c(s, data);
129 av_cold void ff_rdft_end(RDFTContext *s)