1 /*
2 * MDCT/IMDCT transforms
3 * Copyright (c) 2002 Fabrice Bellard
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
22 #include <stdlib.h>
23 #include <string.h>
24 #include "libavutil/common.h"
25 #include "libavutil/libm.h"
26 #include "libavutil/mathematics.h"
27 #include "fft.h"
28 #include "fft-internal.h"
29
30 /**
31 * @file
32 * MDCT/IMDCT transforms.
33 */
34
35 #if FFT_FLOAT
36 # define RSCALE(x, y) ((x) + (y))
37 #else
38 # define RSCALE(x, y) ((int)((x) + (unsigned)(y) + 32) >> 6)
39 #endif
40
41 /**
42 * init MDCT or IMDCT computation.
43 */
ff_mdct_init(FFTContext * s,int nbits,int inverse,double scale)44 av_cold int ff_mdct_init(FFTContext *s, int nbits, int inverse, double scale)
45 {
46 int n, n4, i;
47 double alpha, theta;
48 int tstep;
49
50 memset(s, 0, sizeof(*s));
51 n = 1 << nbits;
52 s->mdct_bits = nbits;
53 s->mdct_size = n;
54 n4 = n >> 2;
55 s->mdct_permutation = FF_MDCT_PERM_NONE;
56
57 if (ff_fft_init(s, s->mdct_bits - 2, inverse) < 0)
58 goto fail;
59
60 s->tcos = av_malloc_array(n/2, sizeof(FFTSample));
61 if (!s->tcos)
62 goto fail;
63
64 switch (s->mdct_permutation) {
65 case FF_MDCT_PERM_NONE:
66 s->tsin = s->tcos + n4;
67 tstep = 1;
68 break;
69 case FF_MDCT_PERM_INTERLEAVE:
70 s->tsin = s->tcos + 1;
71 tstep = 2;
72 break;
73 default:
74 goto fail;
75 }
76
77 theta = 1.0 / 8.0 + (scale < 0 ? n4 : 0);
78 scale = sqrt(fabs(scale));
79 for(i=0;i<n4;i++) {
80 alpha = 2 * M_PI * (i + theta) / n;
81 #if !FFT_FLOAT
82 s->tcos[i*tstep] = lrint(-cos(alpha) * 2147483648.0);
83 s->tsin[i*tstep] = lrint(-sin(alpha) * 2147483648.0);
84 #else
85 s->tcos[i*tstep] = FIX15(-cos(alpha) * scale);
86 s->tsin[i*tstep] = FIX15(-sin(alpha) * scale);
87 #endif
88 }
89 return 0;
90 fail:
91 ff_mdct_end(s);
92 return -1;
93 }
94
95 /**
96 * Compute the middle half of the inverse MDCT of size N = 2^nbits,
97 * thus excluding the parts that can be derived by symmetry
98 * @param output N/2 samples
99 * @param input N/2 samples
100 */
ff_imdct_half_c(FFTContext * s,FFTSample * output,const FFTSample * input)101 void ff_imdct_half_c(FFTContext *s, FFTSample *output, const FFTSample *input)
102 {
103 int k, n8, n4, n2, n, j;
104 const uint16_t *revtab = s->revtab;
105 const FFTSample *tcos = s->tcos;
106 const FFTSample *tsin = s->tsin;
107 const FFTSample *in1, *in2;
108 FFTComplex *z = (FFTComplex *)output;
109
110 n = 1 << s->mdct_bits;
111 n2 = n >> 1;
112 n4 = n >> 2;
113 n8 = n >> 3;
114
115 /* pre rotation */
116 in1 = input;
117 in2 = input + n2 - 1;
118 for(k = 0; k < n4; k++) {
119 j=revtab[k];
120 CMUL(z[j].re, z[j].im, *in2, *in1, tcos[k], tsin[k]);
121 in1 += 2;
122 in2 -= 2;
123 }
124 s->fft_calc(s, z);
125
126 /* post rotation + reordering */
127 for(k = 0; k < n8; k++) {
128 FFTSample r0, i0, r1, i1;
129 CMUL(r0, i1, z[n8-k-1].im, z[n8-k-1].re, tsin[n8-k-1], tcos[n8-k-1]);
130 CMUL(r1, i0, z[n8+k ].im, z[n8+k ].re, tsin[n8+k ], tcos[n8+k ]);
131 z[n8-k-1].re = r0;
132 z[n8-k-1].im = i0;
133 z[n8+k ].re = r1;
134 z[n8+k ].im = i1;
135 }
136 }
137
138 /**
139 * Compute inverse MDCT of size N = 2^nbits
140 * @param output N samples
141 * @param input N/2 samples
142 */
ff_imdct_calc_c(FFTContext * s,FFTSample * output,const FFTSample * input)143 void ff_imdct_calc_c(FFTContext *s, FFTSample *output, const FFTSample *input)
144 {
145 int k;
146 int n = 1 << s->mdct_bits;
147 int n2 = n >> 1;
148 int n4 = n >> 2;
149
150 ff_imdct_half_c(s, output+n4, input);
151
152 for(k = 0; k < n4; k++) {
153 output[k] = -output[n2-k-1];
154 output[n-k-1] = output[n2+k];
155 }
156 }
157
158 /**
159 * Compute MDCT of size N = 2^nbits
160 * @param input N samples
161 * @param out N/2 samples
162 */
ff_mdct_calc_c(FFTContext * s,FFTSample * out,const FFTSample * input)163 void ff_mdct_calc_c(FFTContext *s, FFTSample *out, const FFTSample *input)
164 {
165 int i, j, n, n8, n4, n2, n3;
166 FFTDouble re, im;
167 const uint16_t *revtab = s->revtab;
168 const FFTSample *tcos = s->tcos;
169 const FFTSample *tsin = s->tsin;
170 FFTComplex *x = (FFTComplex *)out;
171
172 n = 1 << s->mdct_bits;
173 n2 = n >> 1;
174 n4 = n >> 2;
175 n8 = n >> 3;
176 n3 = 3 * n4;
177
178 /* pre rotation */
179 for(i=0;i<n8;i++) {
180 re = RSCALE(-input[2*i+n3], - input[n3-1-2*i]);
181 im = RSCALE(-input[n4+2*i], + input[n4-1-2*i]);
182 j = revtab[i];
183 CMUL(x[j].re, x[j].im, re, im, -tcos[i], tsin[i]);
184
185 re = RSCALE( input[2*i] , - input[n2-1-2*i]);
186 im = RSCALE(-input[n2+2*i], - input[ n-1-2*i]);
187 j = revtab[n8 + i];
188 CMUL(x[j].re, x[j].im, re, im, -tcos[n8 + i], tsin[n8 + i]);
189 }
190
191 s->fft_calc(s, x);
192
193 /* post rotation */
194 for(i=0;i<n8;i++) {
195 FFTSample r0, i0, r1, i1;
196 CMUL(i1, r0, x[n8-i-1].re, x[n8-i-1].im, -tsin[n8-i-1], -tcos[n8-i-1]);
197 CMUL(i0, r1, x[n8+i ].re, x[n8+i ].im, -tsin[n8+i ], -tcos[n8+i ]);
198 x[n8-i-1].re = r0;
199 x[n8-i-1].im = i0;
200 x[n8+i ].re = r1;
201 x[n8+i ].im = i1;
202 }
203 }
204
ff_mdct_end(FFTContext * s)205 av_cold void ff_mdct_end(FFTContext *s)
206 {
207 av_freep(&s->tcos);
208 ff_fft_end(s);
209 }
210