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#include "ByteReader.h"
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//
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// constructors
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//
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ByteReader::ByteReader(void)
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{
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	InitVars();
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}
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ByteReader::ByteReader( void* pBuff, DWORD dwSize )
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{
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	Assign( pBuff, dwSize );
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}
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//
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// destructor
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//
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ByteReader::~ByteReader(void)
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{
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}
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//
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// Purpose:
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//   Member variable initializer
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//
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void ByteReader::InitVars()
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{
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	pBuffer       = NULL;
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	cbBuffer      = 0;
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	dwBitsLeft    = dwBitsTotal = 0;
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	byBits2Do     = 8;
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	byCur         = 0;
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	dwIndex       = 0;
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	return;
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}
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//
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// Purpose:
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//   Class initialization handler
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//
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BOOL ByteReader::Assign( void *pBuff, DWORD dwSize )
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{
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	InitVars();
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	if ( !pBuff || !dwSize)
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		return FALSE; // ERR
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	this->pBuffer  = pBuff;
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	this->cbBuffer = dwSize;
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	dwBitsLeft     = dwBitsTotal = dwSize * 8;
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	byCur          = ((PBYTE)pBuff)[ dwIndex++ ];
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	return TRUE; // OK
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}
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DWORD ByteReader::GetUnusedBitCount()
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{
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	return dwBitsLeft;
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}
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DWORD ByteReader::GetTotalBitCount()
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{
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	return dwBitsTotal;
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}
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//
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// Purpose:
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//   Returns the number of accessed bytes
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//
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DWORD ByteReader::GetReadByteCount()
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{
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	DWORD  dwcBitsRead  = (dwBitsTotal - dwBitsLeft);
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	DWORD  c = (DWORD)(dwcBitsRead / 8);
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	if ( dwcBitsRead % 8 ) // round up !
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		++c;
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	return c;
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}
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//
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// Purpose:
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//   The key member function for the buffer querying
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//
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BYTE ByteReader::ReadBit()
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{
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	BYTE bit = 0;
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	if ( dwBitsLeft == 0 )
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		return -1; // ERR
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	bit = byCur & 1;
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	byCur >>= 1;
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	--dwBitsLeft;
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	--byBits2Do;
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	// did we already build a complete byte ? -> paste in buffer
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	if ( !byBits2Do )
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	{
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		byCur = ((PBYTE)pBuffer)[ dwIndex++ ];
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		byBits2Do = 8;
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	}
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	return bit; // OK
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}
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//
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// Purpose:
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//   Read a 1 byte variable from the buffer
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//
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BYTE ByteReader::ReadByte()
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{
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	BYTE byte = 0;
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	for ( UINT i = 0; i < 8; i++ )
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	{
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		byte  |= (ReadBit() << 7);
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		if ( i != 7) // don't shift to last byte !
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            byte >>= 1;
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	}
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	return byte; // OK
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}
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//
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// Purpose:
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//   Read a 2 byte variable from the buffer
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//
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WORD ByteReader::ReadWord()
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{
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	WORD word = 0;
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	for ( UINT i = 0; i < 16; i++ )
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	{
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		word  |= (ReadBit() << 15);
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		if ( i != 15) // don't shift to last byte !
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            word >>= 1;
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	}
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	return word; // OK
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}
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//
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// Purpose:
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//   Read a 4 byte variable from the buffer
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//
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DWORD ByteReader::ReadDword()
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{
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	DWORD dword = 0;
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	for ( UINT i = 0; i < 32; i++ )
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	{
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		dword  |= (ReadBit() << 31);
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		if ( i != 31) // don't shift to last byte !
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            dword >>= 1;
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	}
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	return dword; // OK
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}
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//
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// Purpose:
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//   Read a user defined number of bits from the buffer
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//
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DWORD ByteReader::ReadBits( DWORD dwBitCount )
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{
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	DWORD dword = 0;
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	if ( dwBitCount > 32 )
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		return -1; // ERR
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	for ( UINT i = 0; i < 32; i++ )
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	{
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		if ( i < dwBitCount )
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			dword |= (ReadBit() << 31);
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		if ( i != 31) // don't shift to last byte !
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			dword >>= 1;
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	}
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	return dword; // OK
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}