//========= Copyright � 1996-2005, Valve Corporation, All rights reserved. ============//

 //

 // Purpose: 

 //

 // $NoKeywords: $

 //

 //=============================================================================//

 #include "bitbuf.h"

 #include "coordsize.h"

 #include "vector.h"

 #include "mathlib/math_base.h"

 #include "vstdlib/strtools.h"

 // FIXME: Can't use this until we get multithreaded allocations in tier0 working for tools

 // This is used by VVIS and fails to link

 // NOTE: This must be the last file included!!!

 //#include "tier0/memdbgon.h"

 #ifdef _XBOX

 // mandatory ... wary of above comment and isolating, tier0 is built as MT though

 #include "tier0/memdbgon.h"

 #endif

 static BitBufErrorHandler g_BitBufErrorHandler = 0;

 void InternalBitBufErrorHandler( BitBufErrorType errorType, const char *pDebugName )

 {

 	if ( g_BitBufErrorHandler )

 		g_BitBufErrorHandler( errorType, pDebugName );

 }

 void SetBitBufErrorHandler( BitBufErrorHandler fn )

 {

 	g_BitBufErrorHandler = fn;

 }

 // #define BB_PROFILING

 // Precalculated bit masks for WriteUBitLong. Using these tables instead of 

 // doing the calculations gives a 33% speedup in WriteUBitLong.

 unsigned long g_BitWriteMasks[32][33];

 // (1 << i) - 1

 unsigned long g_ExtraMasks[32];

 class CBitWriteMasksInit

 {

 public:

 	CBitWriteMasksInit()

 	{

 		for( unsigned int startbit=0; startbit < 32; startbit++ )

 		{

 			for( unsigned int nBitsLeft=0; nBitsLeft < 33; nBitsLeft++ )

 			{

 				unsigned int endbit = startbit + nBitsLeft;

 				g_BitWriteMasks[startbit][nBitsLeft] = (1 << startbit) - 1;

 				if(endbit < 32)

 					g_BitWriteMasks[startbit][nBitsLeft] |= ~((1 << endbit) - 1);

 			}

 		}

 		for ( unsigned int maskBit=0; maskBit < 32; maskBit++ )

 			g_ExtraMasks[maskBit] = (1 << maskBit) - 1;

 	}

 };

 CBitWriteMasksInit g_BitWriteMasksInit;

 // ---------------------------------------------------------------------------------------- //

 // bf_write

 // ---------------------------------------------------------------------------------------- //

 bf_write::bf_write()

 {

 	m_pData = NULL;

 	m_nDataBytes = 0;

 	m_nDataBits = -1; // set to -1 so we generate overflow on any operation

 	m_iCurBit = 0;

 	m_bOverflow = false;

 	m_bAssertOnOverflow = true;

 	m_pDebugName = NULL;

 }

 bf_write::bf_write( const char *pDebugName, void *pData, int nBytes, int nBits )

 {

 	m_bAssertOnOverflow = true;

 	m_pDebugName = pDebugName;

 	StartWriting( pData, nBytes, 0, nBits );

 }

 bf_write::bf_write( void *pData, int nBytes, int nBits )

 {

 	m_bAssertOnOverflow = true;

 	StartWriting( pData, nBytes, 0, nBits );

 }

 void bf_write::StartWriting( void *pData, int nBytes, int iStartBit, int nBits )

 {

 	// Make sure it's dword aligned and padded.

 	Assert( (nBytes % 4) == 0 );

 	Assert(((unsigned long)pData & 3) == 0);

 	m_pData = (unsigned char*)pData;

 	m_nDataBytes = nBytes;

 	if ( nBits == -1 )

 	{

 		m_nDataBits = nBytes << 3;

 	}

 	else

 	{

 		Assert( nBits <= nBytes*8 );

 		m_nDataBits = nBits;

 	}

 	m_iCurBit = iStartBit;

 	m_bOverflow = false;

 }

 void bf_write::Reset()

 {

 	m_iCurBit = 0;

 	m_bOverflow = false;

 }

 void bf_write::SetAssertOnOverflow( bool bAssert )

 {

 	m_bAssertOnOverflow = bAssert;

 }

 const char* bf_write::GetDebugName()

 {

 	return m_pDebugName;

 }

 void bf_write::SetDebugName( const char *pDebugName )

 {

 	m_pDebugName = pDebugName;

 }

 void bf_write::SeekToBit( int bitPos )

 {

 	m_iCurBit = bitPos;

 }

 // Sign bit comes first

 void bf_write::WriteSBitLong( int data, int numbits )

 {

 	// Do we have a valid # of bits to encode with?

 	Assert( numbits >= 1 );

 	// Note: it does this wierdness here so it's bit-compatible with regular integer data in the buffer.

 	// (Some old code writes direct integers right into the buffer).

 	if(data < 0)

 	{

 #ifdef _DEBUG

 	if( numbits < 32 )

 	{

 		// Make sure it doesn't overflow.

 		if( data < 0 )

 		{

 			Assert( data >= -(1 << (numbits-1)) );

 		}

 		else

 		{

 			Assert( data < (1 << (numbits-1)) );

 		}

 	}

 #endif

 		WriteUBitLong( (unsigned int)(0x80000000 + data), numbits - 1, false );

 		WriteOneBit( 1 );

 	}

 	else

 	{

 		WriteUBitLong((unsigned int)data, numbits - 1);

 		WriteOneBit( 0 );

 	}

 }

 // writes an unsigned integer with variable bit length

 void bf_write::WriteUBitVar( unsigned int data )

 {

 	unsigned int bits = 0;

 	unsigned int base = 0;

 	while (data > (base<<1))

 	{

 		bits++;

 		base = (1<<bits)-1;

 	}

 	// how many bits do we use

 	if ( bits > 0)

 		WriteUBitLong( 0, bits );

 	// end marker

 	WriteOneBit( 1 );  

 	// write the value

 	if ( bits > 0)

 		WriteUBitLong( data - base , bits );

 }

 void bf_write::WriteBitLong(unsigned int data, int numbits, bool bSigned)

 {

 	if(bSigned)

 		WriteSBitLong((int)data, numbits);

 	else

 		WriteUBitLong(data, numbits);

 }

 bool bf_write::WriteBits(const void *pInData, int nBits)

 {

 #if defined( BB_PROFILING )

 	VPROF( "bf_write::WriteBits" );

 #endif

 	unsigned char *pOut = (unsigned char*)pInData;

 	int nBitsLeft = nBits;

 	if((m_iCurBit+nBits) > m_nDataBits)

 	{

 		SetOverflowFlag();

 		CallErrorHandler( BITBUFERROR_BUFFER_OVERRUN, GetDebugName() );

 		return false;

 	}

 	// Get output dword-aligned.

 	while(((unsigned long)pOut & 3) != 0 && nBitsLeft >= 8)

 	{

 		WriteUBitLong( *pOut, 8, false );

 		++pOut;

 		nBitsLeft -= 8;

 	}

 	// check if we can use fast memcpy if m_iCurBit is byte aligned

 	if ( (nBitsLeft >= 32) && (m_iCurBit & 7) == 0 )

 	{

 		int numbytes = (nBitsLeft >> 3); 

 		int numbits = numbytes << 3;

 		// Bounds checking..

 		// TODO: May not need this check anymore

 		if((m_iCurBit+numbits) > m_nDataBits)

 		{

 			m_iCurBit = m_nDataBits;

 			SetOverflowFlag();

 			CallErrorHandler( BITBUFERROR_BUFFER_OVERRUN, GetDebugName() );

 			return false;

 		}

 		Q_memcpy( m_pData+(m_iCurBit>>3), pOut, numbytes );

 		pOut += numbytes;

 		nBitsLeft -= numbits;

 		m_iCurBit += numbits;

 	}

 	// Read dwords.

 	while(nBitsLeft >= 32)

 	{

 		WriteUBitLong( *((unsigned long*)pOut), 32, false );

 		pOut += sizeof(unsigned long);

 		nBitsLeft -= 32;

 	}

 	// Read the remaining bytes.

 	while(nBitsLeft >= 8)

 	{

 		WriteUBitLong( *pOut, 8, false );

 		++pOut;

 		nBitsLeft -= 8;

 	}

 	// Read the remaining bits.

 	if(nBitsLeft)

 	{

 		WriteUBitLong( *pOut, nBitsLeft, false );

 	}

 	return !IsOverflowed();

 }

 bool bf_write::WriteBitsFromBuffer( bf_read *pIn, int nBits )

 {

 	// This could be optimized a little by

 	while ( nBits > 32 )

 	{

 		WriteUBitLong( pIn->ReadUBitLong( 32 ), 32 );

 		nBits -= 32;

 	}

 	WriteUBitLong( pIn->ReadUBitLong( nBits ), nBits );

 	return !IsOverflowed() && !pIn->IsOverflowed();

 }

 void bf_write::WriteBitAngle( float fAngle, int numbits )

 {

 	int d;

 	unsigned int mask;

 	unsigned int shift;

 	shift = (1<<numbits);

 	mask = shift - 1;

 	d = (int)( (fAngle / 360.0) * shift );

 	d &= mask;

 	WriteUBitLong((unsigned int)d, numbits);

 }

 void bf_write::WriteBitCoord (const float f)

 {

 #if defined( BB_PROFILING )

 	VPROF( "bf_write::WriteBitCoord" );

 #endif

 	int		signbit = (f <= -COORD_RESOLUTION);

 	int		intval = abs(static_cast<int>(f));

 	int		fractval = abs((int)(f*COORD_DENOMINATOR)) & (COORD_DENOMINATOR-1);

 	// Send the bit flags that indicate whether we have an integer part and/or a fraction part.

 	WriteOneBit( intval );

 	WriteOneBit( fractval );

 	if ( intval || fractval )

 	{

 		// Send the sign bit

 		WriteOneBit( signbit );

 		// Send the integer if we have one.

 		if ( intval )

 		{

 			// Adjust the integers from [1..MAX_COORD_VALUE] to [0..MAX_COORD_VALUE-1]

 			intval--;

 			WriteUBitLong( (unsigned int)intval, COORD_INTEGER_BITS );

 		}

 		// Send the fraction if we have one

 		if ( fractval )

 		{

 			WriteUBitLong( (unsigned int)fractval, COORD_FRACTIONAL_BITS );

 		}

 	}

 }

 void bf_write::WriteBitFloat(float val)

 {

 	long intVal;

 	Assert(sizeof(long) == sizeof(float));

 	Assert(sizeof(float) == 4);

 	void *v = &val;

 	intVal = *reinterpret_cast<long *>(v);

 	WriteUBitLong( intVal, 32 );

 }

 void bf_write::WriteBitVec3Coord( const Vector& fa )

 {

 	int		xflag, yflag, zflag;

 	xflag = (fa[0] >= COORD_RESOLUTION) || (fa[0] <= -COORD_RESOLUTION);

 	yflag = (fa[1] >= COORD_RESOLUTION) || (fa[1] <= -COORD_RESOLUTION);

 	zflag = (fa[2] >= COORD_RESOLUTION) || (fa[2] <= -COORD_RESOLUTION);

 	WriteOneBit( xflag );

 	WriteOneBit( yflag );

 	WriteOneBit( zflag );

 	if ( xflag )

 		WriteBitCoord( fa[0] );

 	if ( yflag )

 		WriteBitCoord( fa[1] );

 	if ( zflag )

 		WriteBitCoord( fa[2] );

 }

 void bf_write::WriteBitNormal( float f )

 {

 	int	signbit = (f <= -NORMAL_RESOLUTION);

 	// NOTE: Since +/-1 are valid values for a normal, I'm going to encode that as all ones

 	unsigned int fractval = abs( (int)(f*NORMAL_DENOMINATOR) );

 	// clamp..

 	if (fractval > NORMAL_DENOMINATOR)

 		fractval = NORMAL_DENOMINATOR;

 	// Send the sign bit

 	WriteOneBit( signbit );

 	// Send the fractional component

 	WriteUBitLong( fractval, NORMAL_FRACTIONAL_BITS );

 }

 void bf_write::WriteBitVec3Normal( const Vector& fa )

 {

 	int		xflag, yflag;

 	xflag = (fa[0] >= NORMAL_RESOLUTION) || (fa[0] <= -NORMAL_RESOLUTION);

 	yflag = (fa[1] >= NORMAL_RESOLUTION) || (fa[1] <= -NORMAL_RESOLUTION);

 	WriteOneBit( xflag );

 	WriteOneBit( yflag );

 	if ( xflag )

 		WriteBitNormal( fa[0] );

 	if ( yflag )

 		WriteBitNormal( fa[1] );

 	// Write z sign bit

 	int	signbit = (fa[2] <= -NORMAL_RESOLUTION);

 	WriteOneBit( signbit );

 }

 void bf_write::WriteBitAngles( const QAngle& fa )

 {

 	// FIXME:

 	Vector tmp( fa.x, fa.y, fa.z );

 	WriteBitVec3Coord( tmp );

 }

 void bf_write::WriteChar(int val)

 {

 	WriteSBitLong(val, sizeof(char) << 3);

 }

 void bf_write::WriteByte(int val)

 {

 	WriteUBitLong(val, sizeof(unsigned char) << 3);

 }

 void bf_write::WriteShort(int val)

 {

 	WriteSBitLong(val, sizeof(short) << 3);

 }

 void bf_write::WriteWord(int val)

 {

 	WriteUBitLong(val, sizeof(unsigned short) << 3);

 }

 void bf_write::WriteLong(long val)

 {

 	WriteSBitLong(val, sizeof(long) << 3);

 }

 void bf_write::WriteFloat(float val)

 {

 	WriteBits(&val, sizeof(val) << 3);

 }

 bool bf_write::WriteBytes( const void *pBuf, int nBytes )

 {

 	return WriteBits(pBuf, nBytes << 3);

 }

 bool bf_write::WriteString(const char *pStr)

 {

 	if(pStr)

 	{

 		do

 		{

 			WriteChar( *pStr );

 			++pStr;

 		} while( *(pStr-1) != 0 );

 	}

 	else

 	{

 		WriteChar( 0 );

 	}

 	return !IsOverflowed();

 }

 // ---------------------------------------------------------------------------------------- //

 // bf_read

 // ---------------------------------------------------------------------------------------- //

 bf_read::bf_read()

 {

 	m_pData = NULL;

 	m_nDataBytes = 0;

 	m_nDataBits = -1; // set to -1 so we overflow on any operation

 	m_iCurBit = 0;

 	m_bOverflow = false;

 	m_bAssertOnOverflow = true;

 	m_pDebugName = NULL;

 }

 bf_read::bf_read( const void *pData, int nBytes, int nBits )

 {

 	m_bAssertOnOverflow = true;

 	StartReading( pData, nBytes, 0, nBits );

 }

 bf_read::bf_read( const char *pDebugName, const void *pData, int nBytes, int nBits )

 {

 	m_bAssertOnOverflow = true;

 	m_pDebugName = pDebugName;

 	StartReading( pData, nBytes, 0, nBits );

 }

 void bf_read::StartReading( const void *pData, int nBytes, int iStartBit, int nBits )

 {

 	// Make sure we're dword aligned.

 	Assert(((unsigned long)pData & 3) == 0);

 	m_pData = (unsigned char*)pData;

 	m_nDataBytes = nBytes;

 	if ( nBits == -1 )

 	{

 		m_nDataBits = m_nDataBytes << 3;

 	}

 	else

 	{

 		Assert( nBits <= nBytes*8 );

 		m_nDataBits = nBits;

 	}

 	m_iCurBit = iStartBit;

 	m_bOverflow = false;

 }

 void bf_read::Reset()

 {

 	m_iCurBit = 0;

 	m_bOverflow = false;

 }

 void bf_read::SetAssertOnOverflow( bool bAssert )

 {

 	m_bAssertOnOverflow = bAssert;

 }

 const char* bf_read::GetDebugName()

 {

 	return m_pDebugName;

 }

 void bf_read::SetDebugName( const char *pName )

 {

 	m_pDebugName = pName;

 }

 unsigned int bf_read::CheckReadUBitLong(int numbits)

 {

 	// Ok, just read bits out.

 	int i, nBitValue;

 	unsigned int r = 0;

 	for(i=0; i < numbits; i++)

 	{

 		nBitValue = ReadOneBitNoCheck();

 		r |= nBitValue << i;

 	}

 	m_iCurBit -= numbits;

 	return r;

 }

 bool bf_read::ReadBits(void *pOutData, int nBits)

 {

 #if defined( BB_PROFILING )

 	VPROF( "bf_write::ReadBits" );

 #endif

 	unsigned char *pOut = (unsigned char*)pOutData;

 	int nBitsLeft = nBits;

 	// Get output dword-aligned.

 	while(((unsigned long)pOut & 3) != 0 && nBitsLeft >= 8)

 	{

 		*pOut = (unsigned char)ReadUBitLong(8);

 		++pOut;

 		nBitsLeft -= 8;

 	}

 	// Read dwords.

 	while(nBitsLeft >= 32)

 	{

 		*((unsigned long*)pOut) = ReadUBitLong(32);

 		pOut += sizeof(unsigned long);

 		nBitsLeft -= 32;

 	}

 	// Read the remaining bytes.

 	while(nBitsLeft >= 8)

 	{

 		*pOut = ReadUBitLong(8);

 		++pOut;

 		nBitsLeft -= 8;

 	}

 	// Read the remaining bits.

 	if(nBitsLeft)

 	{

 		*pOut = ReadUBitLong(nBitsLeft);

 	}

 	return !IsOverflowed();

 }

 float bf_read::ReadBitAngle( int numbits )

 {

 	float fReturn;

 	int i;

 	float shift;

 	shift = (float)( 1 << numbits );

 	i = ReadUBitLong( numbits );

 	fReturn = (float)i * (360.0 / shift);

 	return fReturn;

 }

 unsigned int bf_read::PeekUBitLong( int numbits )

 {

 	unsigned int r;

 	int i, nBitValue;

 #ifdef BIT_VERBOSE

 	int nShifts = numbits;

 #endif

 	bf_read savebf;

 	savebf = *this;  // Save current state info

 	r = 0;

 	for(i=0; i < numbits; i++)

 	{

 		nBitValue = ReadOneBit();

 		// Append to current stream

 		if ( nBitValue )

 		{

 			r |= 1 << i;

 		}

 	}

 	*this = savebf;

 #ifdef BIT_VERBOSE

 	Con_Printf( "PeekBitLong:  %i %i\n", nShifts, (unsigned int)r );

 #endif

 	return r;

 }

 // Append numbits least significant bits from data to the current bit stream

 int bf_read::ReadSBitLong( int numbits )

 {

 	int r, sign;

 	r = ReadUBitLong(numbits - 1);

 	// Note: it does this wierdness here so it's bit-compatible with regular integer data in the buffer.

 	// (Some old code writes direct integers right into the buffer).

 	sign = ReadOneBit();

 	if(sign)

 		r = -((1 << (numbits-1)) - r);

 	return r;

 }

 unsigned int bf_read::ReadUBitVar()

 {

 	int bits = 0; // how many bits are used to encode delta offset

 		// how many bits do we use

 	while ( ReadOneBit() == 0 )

 		bits++;

 	unsigned int data = (1<<bits)-1;

 	// read the value

 	if ( bits > 0)

 		data += ReadUBitLong( bits );

 	return data;

 }

 unsigned int bf_read::ReadBitLong(int numbits, bool bSigned)

 {

 	if(bSigned)

 		return (unsigned int)ReadSBitLong(numbits);

 	else

 		return ReadUBitLong(numbits);

 }

 // Basic Coordinate Routines (these contain bit-field size AND fixed point scaling constants)

 float bf_read::ReadBitCoord (void)

 {

 #if defined( BB_PROFILING )

 	VPROF( "bf_write::ReadBitCoord" );

 #endif

 	int		intval=0,fractval=0,signbit=0;

 	float	value = 0.0;

 	// Read the required integer and fraction flags

 	intval = ReadOneBit();

 	fractval = ReadOneBit();

 	// If we got either parse them, otherwise it's a zero.

 	if ( intval || fractval )

 	{

 		// Read the sign bit

 		signbit = ReadOneBit();

 		// If there's an integer, read it in

 		if ( intval )

 		{

 			// Adjust the integers from [0..MAX_COORD_VALUE-1] to [1..MAX_COORD_VALUE]

 			intval = ReadUBitLong( COORD_INTEGER_BITS ) + 1;

 		}

 		// If there's a fraction, read it in

 		if ( fractval )

 		{

 			fractval = ReadUBitLong( COORD_FRACTIONAL_BITS );

 		}

 		// Calculate the correct floating point value

 		value = intval + ((float)fractval * COORD_RESOLUTION);

 		// Fixup the sign if negative.

 		if ( signbit )

 			value = -value;

 	}

 	return value;

 }

 void bf_read::ReadBitVec3Coord( Vector& fa )

 {

 	int		xflag, yflag, zflag;

 	// This vector must be initialized! Otherwise, If any of the flags aren't set, 

 	// the corresponding component will not be read and will be stack garbage.

 	fa.Init( 0, 0, 0 );

 	xflag = ReadOneBit();

 	yflag = ReadOneBit(); 

 	zflag = ReadOneBit();

 	if ( xflag )

 		fa[0] = ReadBitCoord();

 	if ( yflag )

 		fa[1] = ReadBitCoord();

 	if ( zflag )

 		fa[2] = ReadBitCoord();

 }

 float bf_read::ReadBitNormal (void)

 {

 	// Read the sign bit

 	int	signbit = ReadOneBit();

 	// Read the fractional part

 	unsigned int fractval = ReadUBitLong( NORMAL_FRACTIONAL_BITS );

 	// Calculate the correct floating point value

 	float value = (float)fractval * NORMAL_RESOLUTION;

 	// Fixup the sign if negative.

 	if ( signbit )

 		value = -value;

 	return value;

 }

 void bf_read::ReadBitVec3Normal( Vector& fa )

 {

 	int xflag = ReadOneBit();

 	int yflag = ReadOneBit(); 

 	if (xflag)

 		fa[0] = ReadBitNormal();

 	else

 		fa[0] = 0.0f;

 	if (yflag)

 		fa[1] = ReadBitNormal();

 	else

 		fa[1] = 0.0f;

 	// The first two imply the third (but not its sign)

 	int znegative = ReadOneBit();

 	float fafafbfb = fa[0] * fa[0] + fa[1] * fa[1];

 	if (fafafbfb < 1.0f)

 		fa[2] = sqrt( 1.0f - fafafbfb );

 	else

 		fa[2] = 0.0f;

 	if (znegative)

 		fa[2] = -fa[2];

 }

 void bf_read::ReadBitAngles( QAngle& fa )

 {

 	Vector tmp;

 	ReadBitVec3Coord( tmp );

 	fa.Init( tmp.x, tmp.y, tmp.z );

 }

 int bf_read::ReadChar()

 {

 	return ReadSBitLong(sizeof(char) << 3);

 }

 int bf_read::ReadByte()

 {

 	return ReadUBitLong(sizeof(unsigned char) << 3);

 }

 int bf_read::ReadShort()

 {

 	return ReadSBitLong(sizeof(short) << 3);

 }

 int bf_read::ReadWord()

 {

 	return ReadUBitLong(sizeof(unsigned short) << 3);

 }

 long bf_read::ReadLong()

 {

 	return ReadSBitLong(sizeof(long) << 3);

 }

 float bf_read::ReadFloat()

 {

 	float ret;

 	Assert( sizeof(ret) == 4 );

 	ReadBits(&ret, 32);

 	return ret;

 }

 bool bf_read::ReadBytes(void *pOut, int nBytes)

 {

 	return ReadBits(pOut, nBytes << 3);

 }

 bool bf_read::ReadString( char *pStr, int maxLen, bool bLine, int *pOutNumChars )

 {

 	Assert( maxLen != 0 );

 	bool bTooSmall = false;

 	int iChar = 0;

 	while(1)

 	{

 		char val = ReadChar();

 		if ( val == 0 )

 			break;

 		else if ( bLine && val == '\n' )

 			break;

 		if ( iChar < (maxLen-1) )

 		{

 			pStr[iChar] = val;

 			++iChar;

 		}

 		else

 		{

 			bTooSmall = true;

 		}

 	}

 	// Make sure it's null-terminated.

 	Assert( iChar < maxLen );

 	pStr[iChar] = 0;

 	if ( pOutNumChars )

 		*pOutNumChars = iChar;

 	return !IsOverflowed() && !bTooSmall;

 }

 char* bf_read::ReadAndAllocateString( bool *pOverflow )

 {

 	char str[2048];

 	int nChars;

 	bool bOverflow = !ReadString( str, sizeof( str ), false, &nChars );

 	if ( pOverflow )

 		*pOverflow = bOverflow;

 	// Now copy into the output and return it;

 	char *pRet = new char[ nChars + 1 ];

 	for ( int i=0; i <= nChars; i++ )

 		pRet[i] = str[i];

 	return pRet;

 }

 bool bf_read::Seek(int iBit)

 {

 	if(iBit < 0)

 	{

 		SetOverflowFlag();

 		m_iCurBit = m_nDataBits;

 		return false;

 	}

 	else if(iBit > m_nDataBits)

 	{

 		SetOverflowFlag();

 		m_iCurBit = m_nDataBits;

 		return false;

 	}

 	else

 	{

 		m_iCurBit = iBit;