libavcodec/mdct.c

   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 #include "dsputil.h"
  22
  23 /**
  24  * @file libavcodec/mdct.c
  25  * MDCT/IMDCT transforms.
  26  */
  27
  28 // Generate a Kaiser-Bessel Derived Window.
  29 #define BESSEL_I0_ITER 50 // default: 50 iterations of Bessel I0 approximation
  30 av_cold void ff_kbd_window_init(float *window, float alpha, int n)
  31 {
  32    int i, j;
  33    double sum = 0.0, bessel, tmp;
  34    double local_window[n];
  35    double alpha2 = (alpha * M_PI / n) * (alpha * M_PI / n);
  36
  37    for (i = 0; i < n; i++) {
  38        tmp = i * (n - i) * alpha2;
  39        bessel = 1.0;
  40        for (j = BESSEL_I0_ITER; j > 0; j--)
  41            bessel = bessel * tmp / (j * j) + 1;
  42        sum += bessel;
  43        local_window[i] = sum;
  44    }
  45
  46    sum++;
  47    for (i = 0; i < n; i++)
  48        window[i] = sqrt(local_window[i] / sum);
  49 }
  50
  51 DECLARE_ALIGNED(16, float, ff_sine_32  [  32]);
  52 DECLARE_ALIGNED(16, float, ff_sine_64  [  64]);
  53 DECLARE_ALIGNED(16, float, ff_sine_128 [ 128]);
  54 DECLARE_ALIGNED(16, float, ff_sine_256 [ 256]);
  55 DECLARE_ALIGNED(16, float, ff_sine_512 [ 512]);
  56 DECLARE_ALIGNED(16, float, ff_sine_1024[1024]);
  57 DECLARE_ALIGNED(16, float, ff_sine_2048[2048]);
  58 DECLARE_ALIGNED(16, float, ff_sine_4096[4096]);
  59 float * const ff_sine_windows[] = {
  60     NULL, NULL, NULL, NULL, NULL, // unused
  61     ff_sine_32 , ff_sine_64 ,
  62     ff_sine_128, ff_sine_256, ff_sine_512, ff_sine_1024, ff_sine_2048, ff_sine_4096
  63 };
  64
  65 // Generate a sine window.
  66 av_cold void ff_sine_window_init(float *window, int n) {
  67     int i;
  68     for(i = 0; i < n; i++)
  69         window[i] = sinf((i + 0.5) * (M_PI / (2.0 * n)));
  70 }
  71
  72 /**
  73  * init MDCT or IMDCT computation.
  74  */
  75 av_cold int ff_mdct_init(FFTContext *s, int nbits, int inverse, double scale)
  76 {
  77     int n, n4, i;
  78     double alpha, theta;
  79     int tstep;
  80
  81     memset(s, 0, sizeof(*s));
  82     n = 1 << nbits;
  83     s->mdct_bits = nbits;
  84     s->mdct_size = n;
  85     n4 = n >> 2;
  86     s->permutation = FF_MDCT_PERM_NONE;
  87
  88     if (ff_fft_init(s, s->mdct_bits - 2, inverse) < 0)
  89         goto fail;
  90
  91     s->tcos = av_malloc(n/2 * sizeof(FFTSample));
  92     if (!s->tcos)
  93         goto fail;
  94
  95     switch (s->permutation) {
  96     case FF_MDCT_PERM_NONE:
  97         s->tsin = s->tcos + n4;
  98         tstep = 1;
  99         break;
 100     case FF_MDCT_PERM_INTERLEAVE:
 101         s->tsin = s->tcos + 1;
 102         tstep = 2;
 103         break;
 104     default:
 105         goto fail;
 106     }
 107
 108     theta = 1.0 / 8.0 + (scale < 0 ? n4 : 0);
 109     scale = sqrt(fabs(scale));
 110     for(i=0;i<n4;i++) {
 111         alpha = 2 * M_PI * (i + theta) / n;
 112         s->tcos[i*tstep] = -cos(alpha) * scale;
 113         s->tsin[i*tstep] = -sin(alpha) * scale;
 114     }
 115     return 0;
 116  fail:
 117     ff_mdct_end(s);
 118     return -1;
 119 }
 120
 121 /* complex multiplication: p = a * b */
 122 #define CMUL(pre, pim, are, aim, bre, bim) \
 123 {\
 124     FFTSample _are = (are);\
 125     FFTSample _aim = (aim);\
 126     FFTSample _bre = (bre);\
 127     FFTSample _bim = (bim);\
 128     (pre) = _are * _bre - _aim * _bim;\
 129     (pim) = _are * _bim + _aim * _bre;\
 130 }
 131
 132 /**
 133  * Compute the middle half of the inverse MDCT of size N = 2^nbits,
 134  * thus excluding the parts that can be derived by symmetry
 135  * @param output N/2 samples
 136  * @param input N/2 samples
 137  */
 138 void ff_imdct_half_c(FFTContext *s, FFTSample *output, const FFTSample *input)
 139 {
 140     int k, n8, n4, n2, n, j;
 141     const uint16_t *revtab = s->revtab;
 142     const FFTSample *tcos = s->tcos;
 143     const FFTSample *tsin = s->tsin;
 144     const FFTSample *in1, *in2;
 145     FFTComplex *z = (FFTComplex *)output;
 146
 147     n = 1 << s->mdct_bits;
 148     n2 = n >> 1;
 149     n4 = n >> 2;
 150     n8 = n >> 3;
 151
 152     /* pre rotation */
 153     in1 = input;
 154     in2 = input + n2 - 1;
 155     for(k = 0; k < n4; k++) {
 156         j=revtab[k];
 157         CMUL(z[j].re, z[j].im, *in2, *in1, tcos[k], tsin[k]);
 158         in1 += 2;
 159         in2 -= 2;
 160     }
 161     ff_fft_calc(s, z);
 162
 163     /* post rotation + reordering */
 164     for(k = 0; k < n8; k++) {
 165         FFTSample r0, i0, r1, i1;
 166         CMUL(r0, i1, z[n8-k-1].im, z[n8-k-1].re, tsin[n8-k-1], tcos[n8-k-1]);
 167         CMUL(r1, i0, z[n8+k  ].im, z[n8+k  ].re, tsin[n8+k  ], tcos[n8+k  ]);
 168         z[n8-k-1].re = r0;
 169         z[n8-k-1].im = i0;
 170         z[n8+k  ].re = r1;
 171         z[n8+k  ].im = i1;
 172     }
 173 }
 174
 175 /**
 176  * Compute inverse MDCT of size N = 2^nbits
 177  * @param output N samples
 178  * @param input N/2 samples
 179  */
 180 void ff_imdct_calc_c(FFTContext *s, FFTSample *output, const FFTSample *input)
 181 {
 182     int k;
 183     int n = 1 << s->mdct_bits;
 184     int n2 = n >> 1;
 185     int n4 = n >> 2;
 186
 187     ff_imdct_half_c(s, output+n4, input);
 188
 189     for(k = 0; k < n4; k++) {
 190         output[k] = -output[n2-k-1];
 191         output[n-k-1] = output[n2+k];
 192     }
 193 }
 194
 195 /**
 196  * Compute MDCT of size N = 2^nbits
 197  * @param input N samples
 198  * @param out N/2 samples
 199  */
 200 void ff_mdct_calc_c(FFTContext *s, FFTSample *out, const FFTSample *input)
 201 {
 202     int i, j, n, n8, n4, n2, n3;
 203     FFTSample re, im;
 204     const uint16_t *revtab = s->revtab;
 205     const FFTSample *tcos = s->tcos;
 206     const FFTSample *tsin = s->tsin;
 207     FFTComplex *x = (FFTComplex *)out;
 208
 209     n = 1 << s->mdct_bits;
 210     n2 = n >> 1;
 211     n4 = n >> 2;
 212     n8 = n >> 3;
 213     n3 = 3 * n4;
 214
 215     /* pre rotation */
 216     for(i=0;i<n8;i++) {
 217         re = -input[2*i+3*n4] - input[n3-1-2*i];
 218         im = -input[n4+2*i] + input[n4-1-2*i];
 219         j = revtab[i];
 220         CMUL(x[j].re, x[j].im, re, im, -tcos[i], tsin[i]);
 221
 222         re = input[2*i] - input[n2-1-2*i];
 223         im = -(input[n2+2*i] + input[n-1-2*i]);
 224         j = revtab[n8 + i];
 225         CMUL(x[j].re, x[j].im, re, im, -tcos[n8 + i], tsin[n8 + i]);
 226     }
 227
 228     ff_fft_calc(s, x);
 229
 230     /* post rotation */
 231     for(i=0;i<n8;i++) {
 232         FFTSample r0, i0, r1, i1;
 233         CMUL(i1, r0, x[n8-i-1].re, x[n8-i-1].im, -tsin[n8-i-1], -tcos[n8-i-1]);
 234         CMUL(i0, r1, x[n8+i  ].re, x[n8+i  ].im, -tsin[n8+i  ], -tcos[n8+i  ]);
 235         x[n8-i-1].re = r0;
 236         x[n8-i-1].im = i0;
 237         x[n8+i  ].re = r1;
 238         x[n8+i  ].im = i1;
 239     }
 240 }
 241
 242 av_cold void ff_mdct_end(FFTContext *s)
 243 {
 244     av_freep(&s->tcos);
 245     ff_fft_end(s);
 246 }