www.gusucode.com > 一个可以在局域网进行视频聊天的源代码 > 一个可以在局域网进行视频聊天的源代码/VoIP/decoder/GetBits.cpp
////////////////////////////////////////////////////////////////////////////
//
//
// 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 "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;
}