www.pudn.com > shine.zip > l3subband.c

//    Shine is an MP3 encoder 
//    Copyright (C) 1999-2000  Gabriel Bouvigne 
// 
//    This library is free software; you can redistribute it and/or 
//    modify it under the terms of the GNU Library General Public 
//    License as published by the Free Software Foundation; either 
//    version 2 of the License, or (at your option) any later version. 
// 
//    This library is distributed in the hope that it will be useful, 
//    but WITHOUT ANY WARRANTY; without even the implied warranty of 
//    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU 
//    Library General Public License for more details. 
 
 
#include  
 
#include "types.h" 
#include "tables.h"  
#include "l3subband.h" 
 
 
static off[2]    = {0,0}; 
static double x[2][HAN_SIZE]; 
static double filter[SBLIMIT][64]; 
 
void subband_initialise() 
{ 
    int i,j,k; 
 
    for(i=2; i-- ; )  
        for(j=HAN_SIZE; j--; ) 
			x[i][j] = 0; 
         
/* create_ana_filter */ 
/************************************************************************ 
* PURPOSE:  Calculates the analysis filter bank coefficients 
* SEMANTICS: 
* Calculates the analysis filterbank coefficients and rounds to the 
* 9th decimal place accuracy of the filterbank tables in the ISO 
* document.  The coefficients are stored in #filter# 
************************************************************************/ 
   for (i=32; i--; ) 
      for (k=64; k--; )  
      { 
          if ((filter[i][k] = 1e9*cos((double)((2*i+1)*(16-k)*PI64))) >= 0) 
               modf(filter[i][k]+0.5, &filter[i][k]); 
          else 
			  modf(filter[i][k]-0.5, &filter[i][k]); 
          filter[i][k] *= 1e-9; 
      }  
} 
 
 
void window_subband(short **buffer, double z[HAN_SIZE], int k) 
/************************************************************************ 
* PURPOSE:  Overlapping window on PCM samples 
* SEMANTICS: 
* 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# 
************************************************************************/ 
{ 
    int i; 
 
    /* replace 32 oldest samples with 32 new samples */ 
    for (i=0;i<32;i++) 
		x[k][31-i+off[k]] = (double)*(*buffer)++/SCALE; 
 
    /* shift samples into proper window positions */ 
    for (i=HAN_SIZE; i--; ) 
		z[i] = x[k][(i+off[k])&(HAN_SIZE-1)] * enwindow[i]; 
 
    off[k] += 480;              /* offset is modulo (HAN_SIZE)*/ 
    off[k] &= HAN_SIZE-1; 
} 
  
 
void filter_subband(double z[HAN_SIZE], double s[SBLIMIT]) 
 /************************************************************************ 
* PURPOSE:  Calculates the analysis filter bank coefficients 
* SEMANTICS: 
*      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. 
* 
************************************************************************/ 
{ 
   double y[64]; 
   int i,j; 
 
   for (i=64; i--; )  
       for (j=8, y[i] = 0; j--; ) 
		   y[i] += z[i+(j<<6)]; 
 
   for (i=SBLIMIT; i--; ) 
       for (j=64, s[i]= 0; j--; ) 
		   s[i] += filter[i][j] * y[j]; 
}