blob: c318aa83949f25e6b8575b61364e956d56fb5603
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 "rdft.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 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 | s->fft.fft_permute(&s->fft, (FFTComplex*)data); |
69 | s->fft.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 | s->fft.fft_permute(&s->fft, (FFTComplex*)data); |
95 | s->fft.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 ret; |
103 | |
104 | s->nbits = nbits; |
105 | s->inverse = trans == IDFT_C2R || trans == DFT_C2R; |
106 | s->sign_convention = trans == IDFT_R2C || trans == DFT_C2R ? 1 : -1; |
107 | |
108 | if (nbits < 4 || nbits > 16) |
109 | return AVERROR(EINVAL); |
110 | |
111 | if ((ret = ff_fft_init(&s->fft, nbits-1, trans == IDFT_C2R || trans == IDFT_R2C)) < 0) |
112 | return ret; |
113 | |
114 | ff_init_ff_cos_tabs(nbits); |
115 | s->tcos = ff_cos_tabs[nbits]; |
116 | s->tsin = ff_sin_tabs[nbits]+(trans == DFT_R2C || trans == DFT_C2R)*(n>>2); |
117 | #if !CONFIG_HARDCODED_TABLES |
118 | { |
119 | int i; |
120 | const double theta = (trans == DFT_R2C || trans == DFT_C2R ? -1 : 1) * 2 * M_PI / n; |
121 | for (i = 0; i < (n >> 2); i++) |
122 | s->tsin[i] = sin(i * theta); |
123 | } |
124 | #endif |
125 | s->rdft_calc = rdft_calc_c; |
126 | |
127 | if (ARCH_ARM) ff_rdft_init_arm(s); |
128 | |
129 | return 0; |
130 | } |
131 | |
132 | av_cold void ff_rdft_end(RDFTContext *s) |
133 | { |
134 | ff_fft_end(&s->fft); |
135 | } |
136 |