www.pudn.com > wav_mp3_recorder.rar > coder.c

/*
 * coder.c
 *
 * 22/02/01
 * Calculation of coefficient tables for sub band windowing
 * analysis filters and mdct.
 */

#include "types.h"
#include "table1.h"

long int
  x[2][HAN_SIZE],
  z[512];

/*
 * L3_window_filter_subband:
 * -------------------------
 * Overlapping window on PCM samples
 * 32 16-bit pcm samples are scaled to fractional 2's complement and
 * concatenated to the end of the window buffer #x#. The updated window
 * buffer #x# is then windowed by the analysis window #enwindow# to produce
 * the windowed sample #z#
 * The windowed samples #z# is filtered by the digital filter matrix #filter#
 * to produce the subband samples #s#. This done by first selectively
 * picking out values from the windowed samples, and then multiplying
 * them by the filter matrix, producing 32 subband samples.
 */
void L3_window_filter_subband(unsigned long **buffer, long s[SBLIMIT] , int k)
{
  static int off[2];
  long y[64],s1,s2;
  int i,j;

  /* replace 32 oldest samples with 32 new samples */

  /* data format depends on mode */
  if(config.mpeg.channels == 1)
    if(config.wave.channels == 2)
    { /* mono from stereo, sum upper and lower */
      for (i=31;i>=0;i--)
      {
        x[k][i+off[k]] = (((**buffer) >> 16) + (((**buffer) << 16)>>16)) << 15;
        (*buffer)++;
      }
    }
    else
    { /* mono data, use upper then lower */
      for (i=15;i>=0;i--)
      {
        x[k][(2*i)+off[k]+1] = (**buffer) << 16;
        x[k][(2*i)+off[k]] = ((*(*buffer)++) >> 16) << 16;
      }
    }
  else if(k)
  { /* stereo left, use upper */
    for (i=31;i>=0;i--)
      x[k][i+off[k]] = (*(*buffer)++) & 0xffff0000;
  }
  else
  { /* stereo right, use lower */
    for (i=31;i>=0;i--)
      x[k][i+off[k]] = (*(*buffer)++) << 16;
  }

  /* shift samples into proper window positions, and window data */
  for (i=HAN_SIZE; i--; )
    z[i] = mul(x[k][(i+off[k])&(HAN_SIZE-1)],ew[i]);

  off[k] = (off[k] + 480) & (HAN_SIZE-1); /* offset is modulo (HAN_SIZE)*/

  /* sub sample the windowed data */
  for (i=64; i--; )
    for (j=8, y[i] = 0; j--; )
      y[i] += z[i+(j<<6)];

  /* combine sub samples for the simplified matrix calculation */
  for (i=0; i<16; i++)
    y[i+17] += y[15-i];
  for (i=0; i<15; i++)
    y[i+33] -= y[63-i];

  /* simlplified polyphase filter matrix multiplication */
  for (i=16; i--; )
    for (j=0, s[i]= 0, s[31-i]=0; j<32; j += 2)
    {
      s1 = mul(fl[i][j],y[j+16]);
      s2 = mul(fl[i][j+1],y[j+17]);
      s[i] += s1 + s2;
      s[31-i] += s1 - s2;
    }
}

/*
 * L3_mdct_sub:
 * ------------
 */
void L3_mdct_sub(long sb_sample[2][18][SBLIMIT],
                 long mdct_freq[samp_per_frame2])
{
  /* note. we wish to access the array 'mdct_freq[2][2][576]' as
   * [2][2][32][18]. (32*18=576),
   */
  long (*mdct_enc)[18];

  int  ch,gr,band,j,k;
  long mdct_in[36];
  long bu,bd,*m;

 //for(gr=0; gr