www.pudn.com > mp3decode.rar > huffman.c

/**********************************************************************
Copyright (c) 1991 MPEG/audio software simulation group, All Rights Reserved
huffman.c
**********************************************************************/
/**********************************************************************
 * MPEG/audio coding/decoding software, work in progress              *
 *   NOT for public distribution until verified and approved by the   *
 *   MPEG/audio committee.  For further information, please contact   *
 *   Chad Fogg email:                                *
 *                                                                    *
 * VERSION 2.10                                                       *
 *   changes made since last update:                                  *
 *   date   programmers                comment                        *
 *27.2.92   F.O.Witte                  (ITT Intermetall)              *
 *				       email: otto.witte@itt-sc.de    *
 *				       tel:   ++49 (761)517-125	      *
 *				       fax:   ++49 (761)517-880	      *
 *12.6.92   J. Pineda                  Added sign bit to decoder.     *
 * 08/24/93 M. Iwadare                 Changed for 1 pass decoding.   *
 *--------------------------------------------------------------------*
 *  7/14/94 Juergen Koller      Bug fixes in Layer III code           *
 *********************************************************************/	
#include  
#include  

#include "common.h"
#include "huffman.h"
     
HUFFBITS dmask = 1 << (sizeof(HUFFBITS)*8-1);
struct huffcodetab ht[HTN];	/* array of all huffcodtable headers	*/ 
				/* 0..31 Huffman code table 0..31	*/ 
				/* 32,33 count1-tables			*/ 

/* read the huffman decoder table */
int read_decoder_table(FILE *fi) 
{
  int n,i,nn,t;
  unsigned int v0,v1;
  char command[100],line[100];
  for (n=0;nval == NULL) return 2;

  /* table 0 needs no bits */
  if ( h->treelen == 0)
  {  *x = *y = 0;
     return 0;
  }


  /* Lookup in Huffman table. */

  do {
    if (h->val[point][0]==0) {   /*end of tree*/
      *x = h->val[point][1] >> 4;
      *y = h->val[point][1] & 0xf;

      error = 0;
      break;
    } 
    if (hget1bit()) {
      while (h->val[point][1] >= MXOFF) point += h->val[point][1]; 
      point += h->val[point][1];
    }
    else {
      while (h->val[point][0] >= MXOFF) point += h->val[point][0]; 
      point += h->val[point][0];
    }
    level >>= 1;
  } while (level  || (point < ht->treelen) );
  
  /* Check for error. */
  
  if (error) { /* set x and y to a medium value as a simple concealment */
    printf("Illegal Huffman code in data.\n");
    *x = (h->xlen-1 << 1);
    *y = (h->ylen-1 << 1);
  }

  /* Process sign encodings for quadruples tables. */

  if (h->tablename[0] == '3'
      && (h->tablename[1] == '2' || h->tablename[1] == '3')) {
     *v = (*y>>3) & 1;
     *w = (*y>>2) & 1;
     *x = (*y>>1) & 1;
     *y = *y & 1;

     /* v, w, x and y are reversed in the bitstream. 
        switch them around to make test bistream work. */
     
/*   {int i=*v; *v=*y; *y=i; i=*w; *w=*x; *x=i;}  MI */

     if (*v)
        if (hget1bit() == 1) *v = -*v;
     if (*w)
        if (hget1bit() == 1) *w = -*w;
     if (*x)
        if (hget1bit() == 1) *x = -*x;
     if (*y)
        if (hget1bit() == 1) *y = -*y;
     }
     
  /* Process sign and escape encodings for dual tables. */
  
  else {
  
      /* x and y are reversed in the test bitstream.
         Reverse x and y here to make test bitstream work. */
	 
/*    removed 11/11/92 -ag  
		{int i=*x; *x=*y; *y=i;} 
*/      
     if (h->linbits)
       if ((h->xlen-1) == *x) 
         *x += hgetbits(h->linbits);
     if (*x)
        if (hget1bit() == 1) *x = -*x;
     if (h->linbits)	  
       if ((h->ylen-1) == *y)
         *y += hgetbits(h->linbits);
     if (*y)
        if (hget1bit() == 1) *y = -*y;
     }
	  
  return error;  
}