apps/codecs/libwma/mdct.c

   1 /*
   2  * WMA compatible decoder
   3  * Copyright (c) 2002 The FFmpeg Project.
   4  *
   5  * This library is free software; you can redistribute it and/or
   6  * modify it under the terms of the GNU Lesser General Public
   7  * License as published by the Free Software Foundation; either
   8  * version 2 of the License, or (at your option) any later version.
   9  *
  10  * This library is distributed in the hope that it will be useful,
  11  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  12  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  13  * Lesser General Public License for more details.
  14  *
  15  * You should have received a copy of the GNU Lesser General Public
  16  * License along with this library; if not, write to the Free Software
  17  * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
  18  */
  19
  20 #include "wmafixed.h"
  21 #include "mdct.h"
  22
  23 /*these are the sin and cos rotations used by the MDCT*/
  24
  25 /*accessed too infrequently to give much speedup in IRAM*/
  26
  27 fixed32 *tcosarray[5], *tsinarray[5];
  28 fixed32 tcos0[1024], tcos1[512], tcos2[256], tcos3[128], tcos4[64];
  29 fixed32 tsin0[1024], tsin1[512], tsin2[256], tsin3[128], tsin4[64];
  30
  31 uint16_t revtab0[1024];
  32
  33 /**
  34  * init MDCT or IMDCT computation.
  35  */
  36 int ff_mdct_init(MDCTContext *s, int nbits, int inverse)
  37 {
  38     int n, n4, i;
  39
  40     memset(s, 0, sizeof(*s));
  41     n = 1 << nbits;            //nbits ranges from 12 to 8 inclusive
  42     s->nbits = nbits;
  43     s->n = n;
  44     n4 = n >> 2;
  45     s->tcos = tcosarray[12-nbits];
  46     s->tsin = tsinarray[12-nbits];
  47     for(i=0;i<n4;i++)
  48     {
  49
  50         fixed32 ip = itofix32(i) + 0x2000;
  51         ip = ip >> nbits;
  52
  53        /*I can't remember why this works, but it seems to agree for ~24 bits, maybe more!*/
  54         s->tsin[i] = - fsincos(ip<<16, &(s->tcos[i]));
  55         s->tcos[i] *=-1;
  56     }
  57
  58     (&s->fft)->nbits = nbits-2;
  59
  60     (&s->fft)->inverse = inverse;
  61
  62     return 0;
  63
  64 }
  65
  66 /**
  67  * Compute inverse MDCT of size N = 2^nbits
  68  * @param output N samples
  69  * @param input N/2 samples
  70  * @param tmp N/2 samples
  71  */
  72 void ff_imdct_calc(MDCTContext *s,
  73                    fixed32 *output,
  74                    fixed32 *input)
  75 {
  76     int k, n8, n4, n2, n, j,scale;
  77     const fixed32 *tcos = s->tcos;
  78     const fixed32 *tsin = s->tsin;
  79     const fixed32 *in1, *in2;
  80     FFTComplex *z1 = (FFTComplex *)output;
  81     FFTComplex *z2 = (FFTComplex *)input;
  82     int revtabshift = 12 - s->nbits;
  83
  84     n = 1 << s->nbits;
  85
  86     n2 = n >> 1;
  87     n4 = n >> 2;
  88     n8 = n >> 3;
  89
  90
  91     /* pre rotation */
  92     in1 = input;
  93     in2 = input + n2 - 1;
  94
  95     for(k = 0; k < n4; k++)
  96     {
  97         j=revtab0[k<<revtabshift];
  98         CMUL(&z1[j].re, &z1[j].im, *in2, *in1, tcos[k], tsin[k]);
  99         in1 += 2;
 100         in2 -= 2;
 101     }
 102
 103         scale = fft_calc_unscaled(&s->fft, z1);
 104
 105     /* post rotation + reordering */
 106
 107     for(k = 0; k < n4; k++)
 108     {
 109         CMUL(&z2[k].re, &z2[k].im, (z1[k].re), (z1[k].im), tcos[k], tsin[k]);
 110     }
 111
 112     for(k = 0; k < n8; k++)
 113     {
 114         fixed32 r1,r2,r3,r4,r1n,r2n,r3n;
 115
 116         r1 = z2[n8 + k].im;
 117         r1n = r1 * -1;
 118         r2 = z2[n8-1-k].re;
 119         r2n = r2 * -1;
 120         r3 = z2[k+n8].re;
 121         r3n = r3 * -1;
 122         r4 = z2[n8-k-1].im;
 123
 124         output[2*k] = r1n;
 125         output[n2-1-2*k] = r1;
 126
 127         output[2*k+1] = r2;
 128         output[n2-1-2*k-1] = r2n;
 129
 130         output[n2 + 2*k]= r3n;
 131         output[n-1- 2*k]= r3n;
 132
 133         output[n2 + 2*k+1]= r4;
 134         output[n-2 - 2 * k] = r4;
 135     }
 136 }
 137
 138 /* init MDCT */
 139
 140 int mdct_init_global(void)
 141 {
 142     int i,j,m;
 143
 144     /* although seemingly degenerate, these cannot actually be merged together without
 145        a substantial increase in error which is unjustified by the tiny memory savings*/
 146
 147     tcosarray[0] = tcos0; tcosarray[1] = tcos1; tcosarray[2] = tcos2; tcosarray[3] = tcos3;tcosarray[4] = tcos4;
 148     tsinarray[0] = tsin0; tsinarray[1] = tsin1; tsinarray[2] = tsin2; tsinarray[3] = tsin3;tsinarray[4] = tsin4;
 149
 150     /* init the MDCT bit reverse table here rather then in fft_init */
 151
 152     for(i=0;i<1024;i++)           /*hard coded to a 2048 bit rotation*/
 153     {                             /*smaller sizes can reuse the largest*/
 154         m=0;
 155         for(j=0;j<10;j++)
 156         {
 157             m |= ((i >> j) & 1) << (10-j-1);
 158         }
 159
 160        revtab0[i]=m;
 161     }
 162
 163     fft_init_global();
 164
 165     return 0;
 166 }
 167