ecmbuffer.cpp

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/*****************************************************************************
* RelayFax Open Source Project
* Copyright 1996-2004 Alt-N Technologies, Ltd.
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted only as authorized by the RelayFax Open 
* Source License.  A copy of this license is available in file LICENSE 
* in the top-level directory of the distribution.
*
* RelayFax is a registered trademark of Alt-N Technologies, Ltd.
*
* Individual files and/or contributed packages may be copyright by
* other parties and subject to additional restrictions.
*****************************************************************************/

#include "stdafx.h"
#include "ECMBuffer.h"
#include "FaxFile.h"

unsigned short CECMBuffer::fcstab[256] = {
      0x0000, 0x1189, 0x2312, 0x329b, 0x4624, 0x57ad, 0x6536, 0x74bf,
      0x8c48, 0x9dc1, 0xaf5a, 0xbed3, 0xca6c, 0xdbe5, 0xe97e, 0xf8f7,
      0x1081, 0x0108, 0x3393, 0x221a, 0x56a5, 0x472c, 0x75b7, 0x643e,
      0x9cc9, 0x8d40, 0xbfdb, 0xae52, 0xdaed, 0xcb64, 0xf9ff, 0xe876,
      0x2102, 0x308b, 0x0210, 0x1399, 0x6726, 0x76af, 0x4434, 0x55bd,
      0xad4a, 0xbcc3, 0x8e58, 0x9fd1, 0xeb6e, 0xfae7, 0xc87c, 0xd9f5,
      0x3183, 0x200a, 0x1291, 0x0318, 0x77a7, 0x662e, 0x54b5, 0x453c,
      0xbdcb, 0xac42, 0x9ed9, 0x8f50, 0xfbef, 0xea66, 0xd8fd, 0xc974,
      0x4204, 0x538d, 0x6116, 0x709f, 0x0420, 0x15a9, 0x2732, 0x36bb,
      0xce4c, 0xdfc5, 0xed5e, 0xfcd7, 0x8868, 0x99e1, 0xab7a, 0xbaf3,
      0x5285, 0x430c, 0x7197, 0x601e, 0x14a1, 0x0528, 0x37b3, 0x263a,
      0xdecd, 0xcf44, 0xfddf, 0xec56, 0x98e9, 0x8960, 0xbbfb, 0xaa72,
      0x6306, 0x728f, 0x4014, 0x519d, 0x2522, 0x34ab, 0x0630, 0x17b9,
      0xef4e, 0xfec7, 0xcc5c, 0xddd5, 0xa96a, 0xb8e3, 0x8a78, 0x9bf1,
      0x7387, 0x620e, 0x5095, 0x411c, 0x35a3, 0x242a, 0x16b1, 0x0738,
      0xffcf, 0xee46, 0xdcdd, 0xcd54, 0xb9eb, 0xa862, 0x9af9, 0x8b70,
      0x8408, 0x9581, 0xa71a, 0xb693, 0xc22c, 0xd3a5, 0xe13e, 0xf0b7,
      0x0840, 0x19c9, 0x2b52, 0x3adb, 0x4e64, 0x5fed, 0x6d76, 0x7cff,
      0x9489, 0x8500, 0xb79b, 0xa612, 0xd2ad, 0xc324, 0xf1bf, 0xe036,
      0x18c1, 0x0948, 0x3bd3, 0x2a5a, 0x5ee5, 0x4f6c, 0x7df7, 0x6c7e,
	  0xa50a, 0xb483, 0x8618, 0x9791, 0xe32e, 0xf2a7, 0xc03c, 0xd1b5, 
	  0x2942, 0x38cb, 0x0a50, 0x1bd9, 0x6f66, 0x7eef, 0x4c74, 0x5dfd, 
	  0xb58b, 0xa402, 0x9699, 0x8710, 0xf3af, 0xe226, 0xd0bd, 0xc134, 
	  0x39c3, 0x284a, 0x1ad1, 0x0b58, 0x7fe7, 0x6e6e, 0x5cf5, 0x4d7c, 
	  0xc60c, 0xd785, 0xe51e, 0xf497, 0x8028, 0x91a1, 0xa33a, 0xb2b3, 
	  0x4a44, 0x5bcd, 0x6956, 0x78df, 0x0c60, 0x1de9, 0x2f72, 0x3efb, 
	  0xd68d, 0xc704, 0xf59f, 0xe416, 0x90a9, 0x8120, 0xb3bb, 0xa232, 
	  0x5ac5, 0x4b4c, 0x79d7, 0x685e, 0x1ce1, 0x0d68, 0x3ff3, 0x2e7a, 
	  0xe70e, 0xf687, 0xc41c, 0xd595, 0xa12a, 0xb0a3, 0x8238, 0x93b1, 
	  0x6b46, 0x7acf, 0x4854, 0x59dd, 0x2d62, 0x3ceb, 0x0e70, 0x1ff9, 
	  0xf78f, 0xe606, 0xd49d, 0xc514, 0xb1ab, 0xa022, 0x92b9, 0x8330, 
	  0x7bc7, 0x6a4e, 0x58d5, 0x495c, 0x3de3, 0x2c6a, 0x1ef1, 0x0f78 }; 



/*
* Calculate a new fcs given the current fcs and the new data.
*/
unsigned short CECMBuffer::fcs16( register unsigned short fcs, register unsigned char* cp, register int len)
{
  while (len--)
  {
	  fcs = (fcs >> 8) ^ fcstab[(fcs ^ *cp++) & 0xff];
  }
  return (fcs); 
} 


bool CECMBuffer::AddByte( unsigned char nOctet )
{
	if( m_nBytes >= MAX_ECM_FRAME )
	{
		//OutputDebugString( "ECM Buffer overflow\n" );
		m_nBytes = 0;
		return false;
	}

	// flip it
	BYTE nFlippedOctet = CFaxFile::s_FlipTable[nOctet];

	// running checksum computation
	m_FCS = (m_FCS >> 8) ^ fcstab[(m_FCS ^ nFlippedOctet) & 0xff];

	if( m_nBytes < ECM_DATA_HDR )
	{
		// flip the header bytes
		m_Buffer[ m_nBytes++ ] = nFlippedOctet;
	}
	else
	{
		// put the data in without flipping
		m_Buffer[ m_nBytes++ ] = nOctet;
	}

	return true;
}

void CECMBuffer::CalcFCS( unsigned char nOctet )
{
	// running checksum computation
	m_FCS = (m_FCS >> 8) ^ fcstab[(m_FCS ^ nOctet) & 0xff];
	m_nBytes++;
}



bool CECMBuffer::CheckFCS(void)
{
	if( m_nBytes < 4 )
	{
		return false;
	}

	if( m_FCS == PPPGOODFCS16 )
	{
		// mark it as good in the map
		m_SeqMap[ GetSeq() >> 3 ] &= ~(0x01 << (GetSeq() & 0x07 ));

		//OutputDebugString( "FCS Good\n" );
		return true;
	}

	// mark it as bad in the map
	//m_SeqMap[ GetSeq() >> 3 ] |= 0x01 << (GetSeq() & 0x07 );

	//OutputDebugString( "FCS Bad\n" );
	return false;
}


bool CECMBuffer::IsECMBlockGood( int nFrameCount )
{
	BYTE bit,b,newb;
	int i,j;
	int nFrameCtr = 0;
	bool bRet = true;

//	m_SeqMap[2] = 0xff; // DEBUG!!!!

	for (i = 0; i < SEQ_MAP_SIZE; i++ )
	{
		b = m_SeqMap[i];
		newb = 0;

		for( j = 0; j < 8; j++, b >>= 1 )
		{
			bit = (b & 0x01);

			if( nFrameCtr > nFrameCount )
			{
				bit = 0;
			} 
			else if( bit )
			{
				bRet = false;
			}

			newb = (newb << 1) + bit;
			
			nFrameCtr++;
		}

		m_SeqMap[i] = CFaxFile::s_FlipTable[newb];
	}

	return bRet;
}