libavcodec/synth_filter.c

   1 /*
   2  * copyright (c) 2008 Michael Niedermayer <michaelni@gmx.at>
   3  *
   4  * This file is part of FFmpeg.
   5  *
   6  * FFmpeg is free software; you can redistribute it and/or
   7  * modify it under the terms of the GNU Lesser General Public
   8  * License as published by the Free Software Foundation; either
   9  * version 2.1 of the License, or (at your option) any later version.
  10  *
  11  * FFmpeg is distributed in the hope that it will be useful,
  12  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  13  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  14  * Lesser General Public License for more details.
  15  *
  16  * You should have received a copy of the GNU Lesser General Public
  17  * License along with FFmpeg; if not, write to the Free Software
  18  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  19  */
  20
  21 #include "synth_filter.h"
  22
  23 void ff_synth_filter_float(FFTContext *imdct,
  24                            float *synth_buf_ptr, int *synth_buf_offset,
  25                            float synth_buf2[32], const float window[512],
  26                            float out[32], const float in[32], float scale, float bias)
  27 {
  28     float *synth_buf= synth_buf_ptr + *synth_buf_offset;
  29     int i, j;
  30
  31     ff_imdct_half(imdct, synth_buf, in);
  32
  33     for (i = 0; i < 16; i++){
  34         float a= synth_buf2[i     ];
  35         float b= synth_buf2[i + 16];
  36         float c= 0;
  37         float d= 0;
  38         for (j = 0; j < 512 - *synth_buf_offset; j += 64){
  39             a += window[i + j     ]*(-synth_buf[15 - i + j      ]);
  40             b += window[i + j + 16]*( synth_buf[     i + j      ]);
  41             c += window[i + j + 32]*( synth_buf[16 + i + j      ]);
  42             d += window[i + j + 48]*( synth_buf[31 - i + j      ]);
  43         }
  44         for (     ; j < 512; j += 64){
  45             a += window[i + j     ]*(-synth_buf[15 - i + j - 512]);
  46             b += window[i + j + 16]*( synth_buf[     i + j - 512]);
  47             c += window[i + j + 32]*( synth_buf[16 + i + j - 512]);
  48             d += window[i + j + 48]*( synth_buf[31 - i + j - 512]);
  49         }
  50         out[i     ] = a*scale + bias;
  51         out[i + 16] = b*scale + bias;
  52         synth_buf2[i     ] = c;
  53         synth_buf2[i + 16] = d;
  54     }
  55     *synth_buf_offset= (*synth_buf_offset - 32)&511;
  56 }