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_128 [ 128]);
  52 DECLARE_ALIGNED(16, float, ff_sine_256 [ 256]);
  53 DECLARE_ALIGNED(16, float, ff_sine_512 [ 512]);
  54 DECLARE_ALIGNED(16, float, ff_sine_1024[1024]);
  55 DECLARE_ALIGNED(16, float, ff_sine_2048[2048]);
  56 DECLARE_ALIGNED(16, float, ff_sine_4096[4096]);
  57 float *ff_sine_windows[6] = {
  58     ff_sine_128, ff_sine_256, ff_sine_512, ff_sine_1024, ff_sine_2048, ff_sine_4096
  59 };
  60
  61 // Generate a sine window.
  62 av_cold void ff_sine_window_init(float *window, int n) {
  63     int i;
  64     for(i = 0; i < n; i++)
  65         window[i] = sinf((i + 0.5) * (M_PI / (2.0 * n)));
  66 }
  67
  68 /**
  69  * init MDCT or IMDCT computation.
  70  */
  71 av_cold int ff_mdct_init(MDCTContext *s, int nbits, int inverse)
  72 {
  73     int n, n4, i;
  74     double alpha;
  75
  76     memset(s, 0, sizeof(*s));
  77     n = 1 << nbits;
  78     s->nbits = nbits;
  79     s->n = n;
  80     n4 = n >> 2;
  81     s->tcos = av_malloc(n4 * sizeof(FFTSample));
  82     if (!s->tcos)
  83         goto fail;
  84     s->tsin = av_malloc(n4 * sizeof(FFTSample));
  85     if (!s->tsin)
  86         goto fail;
  87
  88     for(i=0;i<n4;i++) {
  89         alpha = 2 * M_PI * (i + 1.0 / 8.0) / n;
  90         s->tcos[i] = -cos(alpha);
  91         s->tsin[i] = -sin(alpha);
  92     }
  93     if (ff_fft_init(&s->fft, s->nbits - 2, inverse) < 0)
  94         goto fail;
  95     return 0;
  96  fail:
  97     av_freep(&s->tcos);
  98     av_freep(&s->tsin);
  99     return -1;
 100 }
 101
 102 /* complex multiplication: p = a * b */
 103 #define CMUL(pre, pim, are, aim, bre, bim) \
 104 {\
 105     FFTSample _are = (are);\
 106     FFTSample _aim = (aim);\
 107     FFTSample _bre = (bre);\
 108     FFTSample _bim = (bim);\
 109     (pre) = _are * _bre - _aim * _bim;\
 110     (pim) = _are * _bim + _aim * _bre;\
 111 }
 112
 113 /**
 114  * Compute the middle half of the inverse MDCT of size N = 2^nbits,
 115  * thus excluding the parts that can be derived by symmetry
 116  * @param output N/2 samples
 117  * @param input N/2 samples
 118  */
 119 void ff_imdct_half_c(MDCTContext *s, FFTSample *output, const FFTSample *input)
 120 {
 121     int k, n8, n4, n2, n, j;
 122     const uint16_t *revtab = s->fft.revtab;
 123     const FFTSample *tcos = s->tcos;
 124     const FFTSample *tsin = s->tsin;
 125     const FFTSample *in1, *in2;
 126     FFTComplex *z = (FFTComplex *)output;
 127
 128     n = 1 << s->nbits;
 129     n2 = n >> 1;
 130     n4 = n >> 2;
 131     n8 = n >> 3;
 132
 133     /* pre rotation */
 134     in1 = input;
 135     in2 = input + n2 - 1;
 136     for(k = 0; k < n4; k++) {
 137         j=revtab[k];
 138         CMUL(z[j].re, z[j].im, *in2, *in1, tcos[k], tsin[k]);
 139         in1 += 2;
 140         in2 -= 2;
 141     }
 142     ff_fft_calc(&s->fft, z);
 143
 144     /* post rotation + reordering */
 145     for(k = 0; k < n8; k++) {
 146         FFTSample r0, i0, r1, i1;
 147         CMUL(r0, i1, z[n8-k-1].im, z[n8-k-1].re, tsin[n8-k-1], tcos[n8-k-1]);
 148         CMUL(r1, i0, z[n8+k  ].im, z[n8+k  ].re, tsin[n8+k  ], tcos[n8+k  ]);
 149         z[n8-k-1].re = r0;
 150         z[n8-k-1].im = i0;
 151         z[n8+k  ].re = r1;
 152         z[n8+k  ].im = i1;
 153     }
 154 }
 155
 156 /**
 157  * Compute inverse MDCT of size N = 2^nbits
 158  * @param output N samples
 159  * @param input N/2 samples
 160  */
 161 void ff_imdct_calc_c(MDCTContext *s, FFTSample *output, const FFTSample *input)
 162 {
 163     int k;
 164     int n = 1 << s->nbits;
 165     int n2 = n >> 1;
 166     int n4 = n >> 2;
 167
 168     ff_imdct_half_c(s, output+n4, input);
 169
 170     for(k = 0; k < n4; k++) {
 171         output[k] = -output[n2-k-1];
 172         output[n-k-1] = output[n2+k];
 173     }
 174 }
 175
 176 /**
 177  * Compute MDCT of size N = 2^nbits
 178  * @param input N samples
 179  * @param out N/2 samples
 180  */
 181 void ff_mdct_calc(MDCTContext *s, FFTSample *out, const FFTSample *input)
 182 {
 183     int i, j, n, n8, n4, n2, n3;
 184     FFTSample re, im;
 185     const uint16_t *revtab = s->fft.revtab;
 186     const FFTSample *tcos = s->tcos;
 187     const FFTSample *tsin = s->tsin;
 188     FFTComplex *x = (FFTComplex *)out;
 189
 190     n = 1 << s->nbits;
 191     n2 = n >> 1;
 192     n4 = n >> 2;
 193     n8 = n >> 3;
 194     n3 = 3 * n4;
 195
 196     /* pre rotation */
 197     for(i=0;i<n8;i++) {
 198         re = -input[2*i+3*n4] - input[n3-1-2*i];
 199         im = -input[n4+2*i] + input[n4-1-2*i];
 200         j = revtab[i];
 201         CMUL(x[j].re, x[j].im, re, im, -tcos[i], tsin[i]);
 202
 203         re = input[2*i] - input[n2-1-2*i];
 204         im = -(input[n2+2*i] + input[n-1-2*i]);
 205         j = revtab[n8 + i];
 206         CMUL(x[j].re, x[j].im, re, im, -tcos[n8 + i], tsin[n8 + i]);
 207     }
 208
 209     ff_fft_calc(&s->fft, x);
 210
 211     /* post rotation */
 212     for(i=0;i<n8;i++) {
 213         FFTSample r0, i0, r1, i1;
 214         CMUL(i1, r0, x[n8-i-1].re, x[n8-i-1].im, -tsin[n8-i-1], -tcos[n8-i-1]);
 215         CMUL(i0, r1, x[n8+i  ].re, x[n8+i  ].im, -tsin[n8+i  ], -tcos[n8+i  ]);
 216         x[n8-i-1].re = r0;
 217         x[n8-i-1].im = i0;
 218         x[n8+i  ].re = r1;
 219         x[n8+i  ].im = i1;
 220     }
 221 }
 222
 223 av_cold void ff_mdct_end(MDCTContext *s)
 224 {
 225     av_freep(&s->tcos);
 226     av_freep(&s->tsin);
 227     ff_fft_end(&s->fft);
 228 }