////////////////////////////////////////////////////////////////////////////
//
//
//    Project     : VideoNet version 1.1.
//    Description : Peer to Peer Video Conferencing over the LAN.
//	  Author      :	Nagareshwar Y Talekar ( nsry2002@yahoo.co.in)
//    Date        : 15-6-2004.
//
//    This is the modified version of tmndecode (H.263 decoder) 
//    written by Karl & Robert.It was in ANSI C. I have converted into C++
//    so that it can be integrated into any windows application. I have 
//    removed some of the files which had display and file storing 
//    functions.I have removed the unnecessary code and also added some
//    new files..
//	  Original library dealt with files. Input & Output , both were files.
//    I have done some major changes so that it can be used for real time 
//    decoding process. Now one can use this library for decoding H263 frames. 
//
//
//    File description : 
//    Name    : GetBits.cpp
//
/////////////////////////////////////////////////////////////////////////////


/************************************************************************
 *
 *  getbits.c, bit level routines for tmndecode (H.263 decoder)
 *  Copyright (C) 1996  Telenor R&D, Norway
 *        Karl Olav Lillevold <Karl.Lillevold@nta.no>
 *
 *  This program is free software; you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License as published by
 *  the Free Software Foundation; either version 2 of the License, or
 *  (at your option) any later version.
 *
 *  This program 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 General Public License for more details.
 *
 *  You should have received a copy of the GNU General Public License
 *  along with this program; if not, write to the Free Software
 *  Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
 *
 *  Karl Olav Lillevold               <Karl.Lillevold@nta.no>
 *  Telenor Research and Development
 *  P.O.Box 83                        tel.:   +47 63 84 84 00
 *  N-2007 Kjeller, Norway            fax.:   +47 63 81 00 76
 *
 *  Robert Danielsen                  e-mail: Robert.Danielsen@nta.no
 *  Telenor Research and Development  www:    http://www.nta.no/brukere/DVC/
 *  P.O.Box 83                        tel.:   +47 63 84 84 00
 *  N-2007 Kjeller, Norway            fax.:   +47 63 81 00 76
 *  
 ************************************************************************/

/*
 * based on mpeg2decode, (C) 1994, MPEG Software Simulation Group
 * and mpeg2play, (C) 1994 Stefan Eckart
 *                         <stefan@lis.e-technik.tu-muenchen.de>
 *
 */

#include "stdafx.h"
#include "GetBits.h"


/* to mask the n least significant bits of an integer */

static unsigned int msk[33] =
{
  0x00000000,0x00000001,0x00000003,0x00000007,
  0x0000000f,0x0000001f,0x0000003f,0x0000007f,
  0x000000ff,0x000001ff,0x000003ff,0x000007ff,
  0x00000fff,0x00001fff,0x00003fff,0x00007fff,
  0x0000ffff,0x0001ffff,0x0003ffff,0x0007ffff,
  0x000fffff,0x001fffff,0x003fffff,0x007fffff,
  0x00ffffff,0x01ffffff,0x03ffffff,0x07ffffff,
  0x0fffffff,0x1fffffff,0x3fffffff,0x7fffffff,
  0xffffffff
};


/* initialize buffer, call once before first getbits or showbits */

void initbits()
{
  ld->incnt = 0;
  ld->rdptr = ld->rdbfr + 2048;
  ld->bitcnt = 0;
}

/*
*		Read bytes from buffer
*
*/
void fillbfr()
{
  int l;

  // Store prev 4 bytes into first 4 bytes....
  // new data is appended to these prev bytes....
  ld->inbfr[0] = ld->inbfr[8];
  ld->inbfr[1] = ld->inbfr[9];
  ld->inbfr[2] = ld->inbfr[10];
  ld->inbfr[3] = ld->inbfr[11];

// check if whether we have to read the data. ..or it already exist

  if (ld->rdptr>=ld->rdbfr+2048)
  {
      // copy the data from buffer..
	  // ....2048 bytes at a time...
	  if(csize>=2048)
	  {
	  memcpy(ld->rdbfr,cframe+cindex,2048);
	  l=2048;
	  cindex+=2048;
	  csize-=2048;
	  }
	  else
	  {
			// Read all available data from buffer
			if(csize>0)
			{
		    memcpy(ld->rdbfr,cframe+cindex,csize);
			l=csize;
			cindex+=csize;
			csize=0;

			}
			else  // buffer is empty
			{
			l=0;
			csize=0;
			}
	  }
   
	// reset the pointer...to start of data
	  ld->rdptr = ld->rdbfr;
    
	  
	  // if less data is read....then append "End Sequence code"
	  if (l<2048)
	  {
			  if (l<0)
				l = 0;

			  while (l<2048)   /* Add recognizable sequence end code */
			  {
				ld->rdbfr[l++] = 0;
				ld->rdbfr[l++] = 0;
				ld->rdbfr[l++] = (1<<7) | (SE_CODE<<2);
			  }
	  }
  
  
  }


  // store 8 byte of data into in buffer
  for (l=0; l<8; l++)
    ld->inbfr[l+4] = ld->rdptr[l];

  //update pointers..
  ld->rdptr+= 8;		// 8 bytes..
  ld->incnt+= 64;       // 64 bits...

}


/* return next n bits (right adjusted) without advancing */

unsigned int showbits(int n)
{
  unsigned char *v;
  unsigned int b;
  int c;

//if inbuf contains less bits...then read again....
  if (ld->incnt<n)
    fillbfr();

  // get pointer to start data in inbuffer
  //
  v = ld->inbfr + ((96 - ld->incnt)>>3);
  
  // combine bytes to form int
  b = (v[0]<<24) | (v[1]<<16) | (v[2]<<8) | v[3];
  
  c = ((ld->incnt-1) & 7) + 25;
  
  //send the righ adjusted value....
  return (b>>(c-n)) & msk[n];
}


/* return next bit (could be made faster than getbits(1)) */

unsigned int getbits1()
{
  return getbits(1);
}


/* advance by n bits */
// Update the pointer....
// === Remove data from the buffer...
void flushbits(int n)
{

  ld->bitcnt+= n;
  ld->incnt-= n;
  if (ld->incnt < 0)
    fillbfr();
}


/* return next n bits (right adjusted) */
//
// Get next n bits from the file header...
//
unsigned int getbits(int n)
{
  unsigned int l;

  l = showbits(n);
  flushbits(n);

  return l;
}