www.pudn.com > h263_.rar > Sarcode.cpp

// Sarcode.cpp: implementation of the CSarcode class. 
// 
////////////////////////////////////////////////////////////////////// 
 
#include "stdafx.h" 
#include "ÊÓƵ±à½âÂëÆ÷.h" 
#include "Sarcode.h" 
 
#ifdef _DEBUG 
#undef THIS_FILE 
static char THIS_FILE[]=__FILE__; 
#define new DEBUG_NEW 
#endif 
 
////////////////////////////////////////////////////////////////////// 
// Construction/Destruction 
////////////////////////////////////////////////////////////////////// 
#define   q1    16384 
#define   q2    32768 
#define   q3    49152 
#define   top   65535 
 
 
CSarcode::CSarcode() 
{ 
     zerorun=0; 
} 
 
CSarcode::~CSarcode() 
{ 
 
} 
 
 
int CSarcode::decode_a_symbol(int cumul_freq[]) 
{ 
  length = high - low + 1; 
  cum = (-1 + (code_value - low + 1) * cumul_freq[0]) / length; 
  for (sacindex = 1; cumul_freq[sacindex] > cum; sacindex++); 
  high = low - 1 + (length * cumul_freq[sacindex-1]) / cumul_freq[0]; 
  low += (length * cumul_freq[sacindex]) / cumul_freq[0]; 
 
  for ( ; ; )  
  {   
    if (high < q2) ; 
    else if (low >= q2)  
	{ 
      code_value -= q2;  
      low -= q2;  
      high -= q2; 
    } 
    else if (low >= q1 && high < q3)  
	{ 
      code_value -= q1;  
      low -= q1;  
      high -= q1; 
    } 
    else  
	    break; 
      
    low *= 2;  
    high = 2*high + 1; 
    bit_out_psc_layer();  
    code_value = 2*code_value + bit; 
  } 
 
  return (sacindex-1); 
 
} 
/////// 
void CSarcode::bit_out_psc_layer() 
{ 
  if (m_getbits.showbits(17)!=1) 
  { // check for startcode in Arithmetic Decoder FIFO  
 
    bit = m_getbits.getbits(1); 
    if(zerorun > 13)  
	{	/* if number of consecutive zeros = 14 */	  
      if (!bit)  
	  { 
	    AfxMessageBox("PSC/GBSC, Header Data, or Encoded Stream Error !"); 
	    zerorun = 1;		 
      } 
      else  
	  { /* if there is a 'stuffing bit present */ 
	    AfxMessageBox("Removing Startcode Emulation Prevention bit!"); 
    	bit = m_getbits.getbits(1); 	/* overwrite the last bit */	 
	    zerorun = !bit;	  	/* zerorun=1 if bit is a '0' */ 
      } 
    } 
    else 
	{ /* if consecutive zero's not exceeded 14 */ 
      if (!bit) 
    	zerorun++; 
      else 
	    zerorun = 0; 
    } 
 
  } /* end of if !(showbits(17)) */ 
 
  else  
  { 
    bit = 0; 
    AfxMessageBox("Startcode Found:Finishing Arithmetic Decoding using 'Garbage bits'!"); 
  } 
 
} 
 
void CSarcode::decoder_reset() 
{ 
 int i; 
  zerorun = 0;			/* clear consecutive zero's counter */ 
  code_value = 0; 
  low = 0; 
  high = top; 
  for (i = 1; i <= 16; i++) 
  { 
    bit_out_psc_layer();  
    code_value = 2 * code_value + bit; 
  } 
}