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/mathematics.h" 26#include "fft.h" 27 28/** 29 * @file 30 * MDCT/IMDCT transforms. 31 */ 32 33// Generate a Kaiser-Bessel Derived Window. 34#define BESSEL_I0_ITER 50 // default: 50 iterations of Bessel I0 approximation 35av_cold void ff_kbd_window_init(float *window, float alpha, int n) 36{ 37 int i, j; 38 double sum = 0.0, bessel, tmp; 39 double local_window[n]; 40 double alpha2 = (alpha * M_PI / n) * (alpha * M_PI / n); 41 42 for (i = 0; i < n; i++) { 43 tmp = i * (n - i) * alpha2; 44 bessel = 1.0; 45 for (j = BESSEL_I0_ITER; j > 0; j--) 46 bessel = bessel * tmp / (j * j) + 1; 47 sum += bessel; 48 local_window[i] = sum; 49 } 50 51 sum++; 52 for (i = 0; i < n; i++) 53 window[i] = sqrt(local_window[i] / sum); 54} 55 56#include "mdct_tablegen.h" 57 58/** 59 * init MDCT or IMDCT computation. 60 */ 61av_cold int ff_mdct_init(FFTContext *s, int nbits, int inverse, double scale) 62{ 63 int n, n4, i; 64 double alpha, theta; 65 int tstep; 66 67 memset(s, 0, sizeof(*s)); 68 n = 1 << nbits; 69 s->mdct_bits = nbits; 70 s->mdct_size = n; 71 n4 = n >> 2; 72 s->permutation = FF_MDCT_PERM_NONE; 73 74 if (ff_fft_init(s, s->mdct_bits - 2, inverse) < 0) 75 goto fail; 76 77 s->tcos = av_malloc(n/2 * sizeof(FFTSample)); 78 if (!s->tcos) 79 goto fail; 80 81 switch (s->permutation) { 82 case FF_MDCT_PERM_NONE: 83 s->tsin = s->tcos + n4; 84 tstep = 1; 85 break; 86 case FF_MDCT_PERM_INTERLEAVE: 87 s->tsin = s->tcos + 1; 88 tstep = 2; 89 break; 90 default: 91 goto fail; 92 } 93 94 theta = 1.0 / 8.0 + (scale < 0 ? n4 : 0); 95 scale = sqrt(fabs(scale)); 96 for(i=0;i<n4;i++) { 97 alpha = 2 * M_PI * (i + theta) / n; 98 s->tcos[i*tstep] = -cos(alpha) * scale; 99 s->tsin[i*tstep] = -sin(alpha) * scale; 100 } 101 return 0; 102 fail: 103 ff_mdct_end(s); 104 return -1; 105} 106 107/* complex multiplication: p = a * b */ 108#define CMUL(pre, pim, are, aim, bre, bim) \ 109{\ 110 FFTSample _are = (are);\ 111 FFTSample _aim = (aim);\ 112 FFTSample _bre = (bre);\ 113 FFTSample _bim = (bim);\ 114 (pre) = _are * _bre - _aim * _bim;\ 115 (pim) = _are * _bim + _aim * _bre;\ 116} 117 118/** 119 * Compute the middle half of the inverse MDCT of size N = 2^nbits, 120 * thus excluding the parts that can be derived by symmetry 121 * @param output N/2 samples 122 * @param input N/2 samples 123 */ 124void ff_imdct_half_c(FFTContext *s, FFTSample *output, const FFTSample *input) 125{ 126 int k, n8, n4, n2, n, j; 127 const uint16_t *revtab = s->revtab; 128 const FFTSample *tcos = s->tcos; 129 const FFTSample *tsin = s->tsin; 130 const FFTSample *in1, *in2; 131 FFTComplex *z = (FFTComplex *)output; 132 133 n = 1 << s->mdct_bits; 134 n2 = n >> 1; 135 n4 = n >> 2; 136 n8 = n >> 3; 137 138 /* pre rotation */ 139 in1 = input; 140 in2 = input + n2 - 1; 141 for(k = 0; k < n4; k++) { 142 j=revtab[k]; 143 CMUL(z[j].re, z[j].im, *in2, *in1, tcos[k], tsin[k]); 144 in1 += 2; 145 in2 -= 2; 146 } 147 ff_fft_calc(s, z); 148 149 /* post rotation + reordering */ 150 for(k = 0; k < n8; k++) { 151 FFTSample r0, i0, r1, i1; 152 CMUL(r0, i1, z[n8-k-1].im, z[n8-k-1].re, tsin[n8-k-1], tcos[n8-k-1]); 153 CMUL(r1, i0, z[n8+k ].im, z[n8+k ].re, tsin[n8+k ], tcos[n8+k ]); 154 z[n8-k-1].re = r0; 155 z[n8-k-1].im = i0; 156 z[n8+k ].re = r1; 157 z[n8+k ].im = i1; 158 } 159} 160 161/** 162 * Compute inverse MDCT of size N = 2^nbits 163 * @param output N samples 164 * @param input N/2 samples 165 */ 166void ff_imdct_calc_c(FFTContext *s, FFTSample *output, const FFTSample *input) 167{ 168 int k; 169 int n = 1 << s->mdct_bits; 170 int n2 = n >> 1; 171 int n4 = n >> 2; 172 173 ff_imdct_half_c(s, output+n4, input); 174 175 for(k = 0; k < n4; k++) { 176 output[k] = -output[n2-k-1]; 177 output[n-k-1] = output[n2+k]; 178 } 179} 180 181/** 182 * Compute MDCT of size N = 2^nbits 183 * @param input N samples 184 * @param out N/2 samples 185 */ 186void ff_mdct_calc_c(FFTContext *s, FFTSample *out, const FFTSample *input) 187{ 188 int i, j, n, n8, n4, n2, n3; 189 FFTSample re, im; 190 const uint16_t *revtab = s->revtab; 191 const FFTSample *tcos = s->tcos; 192 const FFTSample *tsin = s->tsin; 193 FFTComplex *x = (FFTComplex *)out; 194 195 n = 1 << s->mdct_bits; 196 n2 = n >> 1; 197 n4 = n >> 2; 198 n8 = n >> 3; 199 n3 = 3 * n4; 200 201 /* pre rotation */ 202 for(i=0;i<n8;i++) { 203 re = -input[2*i+3*n4] - input[n3-1-2*i]; 204 im = -input[n4+2*i] + input[n4-1-2*i]; 205 j = revtab[i]; 206 CMUL(x[j].re, x[j].im, re, im, -tcos[i], tsin[i]); 207 208 re = input[2*i] - input[n2-1-2*i]; 209 im = -(input[n2+2*i] + input[n-1-2*i]); 210 j = revtab[n8 + i]; 211 CMUL(x[j].re, x[j].im, re, im, -tcos[n8 + i], tsin[n8 + i]); 212 } 213 214 ff_fft_calc(s, x); 215 216 /* post rotation */ 217 for(i=0;i<n8;i++) { 218 FFTSample r0, i0, r1, i1; 219 CMUL(i1, r0, x[n8-i-1].re, x[n8-i-1].im, -tsin[n8-i-1], -tcos[n8-i-1]); 220 CMUL(i0, r1, x[n8+i ].re, x[n8+i ].im, -tsin[n8+i ], -tcos[n8+i ]); 221 x[n8-i-1].re = r0; 222 x[n8-i-1].im = i0; 223 x[n8+i ].re = r1; 224 x[n8+i ].im = i1; 225 } 226} 227 228av_cold void ff_mdct_end(FFTContext *s) 229{ 230 av_freep(&s->tcos); 231 ff_fft_end(s); 232} 233