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 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 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 // Generate a sine window.
  52 void ff_sine_window_init(float *window, int n) {
  53     int i;
  54     for(i = 0; i < n; i++)
  55         window[i] = sin((i + 0.5) / (2 * n) * M_PI);
  56 }
  57
  58 /**
  59  * init MDCT or IMDCT computation.
  60  */
  61 int ff_mdct_init(MDCTContext *s, int nbits, int inverse)
  62 {
  63     int n, n4, i;
  64     double alpha;
  65
  66     memset(s, 0, sizeof(*s));
  67     n = 1 << nbits;
  68     s->nbits = nbits;
  69     s->n = n;
  70     n4 = n >> 2;
  71     s->tcos = av_malloc(n4 * sizeof(FFTSample));
  72     if (!s->tcos)
  73         goto fail;
  74     s->tsin = av_malloc(n4 * sizeof(FFTSample));
  75     if (!s->tsin)
  76         goto fail;
  77
  78     for(i=0;i<n4;i++) {
  79         alpha = 2 * M_PI * (i + 1.0 / 8.0) / n;
  80         s->tcos[i] = -cos(alpha);
  81         s->tsin[i] = -sin(alpha);
  82     }
  83     if (ff_fft_init(&s->fft, s->nbits - 2, inverse) < 0)
  84         goto fail;
  85     return 0;
  86  fail:
  87     av_freep(&s->tcos);
  88     av_freep(&s->tsin);
  89     return -1;
  90 }
  91
  92 /* complex multiplication: p = a * b */
  93 #define CMUL(pre, pim, are, aim, bre, bim) \
  94 {\
  95     double _are = (are);\
  96     double _aim = (aim);\
  97     double _bre = (bre);\
  98     double _bim = (bim);\
  99     (pre) = _are * _bre - _aim * _bim;\
 100     (pim) = _are * _bim + _aim * _bre;\
 101 }
 102
 103 static void imdct_c(MDCTContext *s, const FFTSample *input, FFTSample *tmp)
 104 {
 105     int k, n4, n2, n, j;
 106     const uint16_t *revtab = s->fft.revtab;
 107     const FFTSample *tcos = s->tcos;
 108     const FFTSample *tsin = s->tsin;
 109     const FFTSample *in1, *in2;
 110     FFTComplex *z = (FFTComplex *)tmp;
 111
 112     n = 1 << s->nbits;
 113     n2 = n >> 1;
 114     n4 = n >> 2;
 115
 116     /* pre rotation */
 117     in1 = input;
 118     in2 = input + n2 - 1;
 119     for(k = 0; k < n4; k++) {
 120         j=revtab[k];
 121         CMUL(z[j].re, z[j].im, *in2, *in1, tcos[k], tsin[k]);
 122         in1 += 2;
 123         in2 -= 2;
 124     }
 125     ff_fft_calc(&s->fft, z);
 126
 127     /* post rotation + reordering */
 128     /* XXX: optimize */
 129     for(k = 0; k < n4; k++) {
 130         CMUL(z[k].re, z[k].im, z[k].re, z[k].im, tcos[k], tsin[k]);
 131     }
 132 }
 133
 134 /**
 135  * Compute inverse MDCT of size N = 2^nbits
 136  * @param output N samples
 137  * @param input N/2 samples
 138  * @param tmp N/2 samples
 139  */
 140 void ff_imdct_calc(MDCTContext *s, FFTSample *output,
 141                    const FFTSample *input, FFTSample *tmp)
 142 {
 143     int k, n8, n2, n;
 144     FFTComplex *z = (FFTComplex *)tmp;
 145     n = 1 << s->nbits;
 146     n2 = n >> 1;
 147     n8 = n >> 3;
 148
 149     imdct_c(s, input, tmp);
 150
 151     for(k = 0; k < n8; k++) {
 152         output[2*k] = -z[n8 + k].im;
 153         output[n2-1-2*k] = z[n8 + k].im;
 154
 155         output[2*k+1] = z[n8-1-k].re;
 156         output[n2-1-2*k-1] = -z[n8-1-k].re;
 157
 158         output[n2 + 2*k]=-z[k+n8].re;
 159         output[n-1- 2*k]=-z[k+n8].re;
 160
 161         output[n2 + 2*k+1]=z[n8-k-1].im;
 162         output[n-2 - 2 * k] = z[n8-k-1].im;
 163     }
 164 }
 165
 166 /**
 167  * Compute the middle half of the inverse MDCT of size N = 2^nbits,
 168  * thus excluding the parts that can be derived by symmetry
 169  * @param output N/2 samples
 170  * @param input N/2 samples
 171  * @param tmp N/2 samples
 172  */
 173 void ff_imdct_half(MDCTContext *s, FFTSample *output,
 174                    const FFTSample *input, FFTSample *tmp)
 175 {
 176     int k, n8, n4, n;
 177     FFTComplex *z = (FFTComplex *)tmp;
 178     n = 1 << s->nbits;
 179     n4 = n >> 2;
 180     n8 = n >> 3;
 181
 182     imdct_c(s, input, tmp);
 183
 184     for(k = 0; k < n8; k++) {
 185         output[n4-1-2*k]   =  z[n8+k].im;
 186         output[n4-1-2*k-1] = -z[n8-k-1].re;
 187         output[n4 + 2*k]   = -z[n8+k].re;
 188         output[n4 + 2*k+1] =  z[n8-k-1].im;
 189     }
 190 }
 191
 192 /**
 193  * Compute MDCT of size N = 2^nbits
 194  * @param input N samples
 195  * @param out N/2 samples
 196  * @param tmp temporary storage of N/2 samples
 197  */
 198 void ff_mdct_calc(MDCTContext *s, FFTSample *out,
 199                   const FFTSample *input, FFTSample *tmp)
 200 {
 201     int i, j, n, n8, n4, n2, n3;
 202     FFTSample re, im, re1, im1;
 203     const uint16_t *revtab = s->fft.revtab;
 204     const FFTSample *tcos = s->tcos;
 205     const FFTSample *tsin = s->tsin;
 206     FFTComplex *x = (FFTComplex *)tmp;
 207
 208     n = 1 << s->nbits;
 209     n2 = n >> 1;
 210     n4 = n >> 2;
 211     n8 = n >> 3;
 212     n3 = 3 * n4;
 213
 214     /* pre rotation */
 215     for(i=0;i<n8;i++) {
 216         re = -input[2*i+3*n4] - input[n3-1-2*i];
 217         im = -input[n4+2*i] + input[n4-1-2*i];
 218         j = revtab[i];
 219         CMUL(x[j].re, x[j].im, re, im, -tcos[i], tsin[i]);
 220
 221         re = input[2*i] - input[n2-1-2*i];
 222         im = -(input[n2+2*i] + input[n-1-2*i]);
 223         j = revtab[n8 + i];
 224         CMUL(x[j].re, x[j].im, re, im, -tcos[n8 + i], tsin[n8 + i]);
 225     }
 226
 227     ff_fft_calc(&s->fft, x);
 228
 229     /* post rotation */
 230     for(i=0;i<n4;i++) {
 231         re = x[i].re;
 232         im = x[i].im;
 233         CMUL(re1, im1, re, im, -tsin[i], -tcos[i]);
 234         out[2*i] = im1;
 235         out[n2-1-2*i] = re1;
 236     }
 237 }
 238
 239 void ff_mdct_end(MDCTContext *s)
 240 {
 241     av_freep(&s->tcos);
 242     av_freep(&s->tsin);
 243     ff_fft_end(&s->fft);
 244 }