// BitsReader.h:  bits reader, for Gnash.
// 
//   Copyright (C) 2005, 2006, 2007, 2008, 2009, 2010, 2011, 2012
//   Free Software Foundation, Inc
// 
// 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 3 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., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
//


#ifndef BITSREADER_H
#define BITSREADER_H

#include "dsodefs.h"
#include "log.h"

#include <cassert>
#include <boost/cstdint.hpp> // for boost::uint32_t used in this file

namespace gnash {

/// BitsReader is used to encapsulate bit-packed buffer reads.
//
/// TODO: implement boundary checking, maybe by throwing an exception
///       when attempts are made to read past end of buffer
///
class DSOEXPORT BitsReader 
{
public:
	typedef unsigned char byte;

	/// Ownership of buffer left to caller
	BitsReader(const byte* input, size_t len)
		:
		start(input),
		ptr(start),
		end(start+len),
		usedBits(0)
	{
	}

	/// Create a BitsReader reading a subset of another
	//
	/// The starting pointer will be taken from the parent
	/// reader cursor, including used bits, use align() if
	/// need to discard the left over ones.
	///
	/// length will be given explicitly.
	///
	BitsReader(const BitsReader& from, size_t len)
		:
		start(from.ptr),
		ptr(start),
		end(start+len),
		usedBits(from.usedBits) 
	{
	}

	~BitsReader() {}

	size_t size() const
	{
		return end-start;
	}

	/// Set a new buffer to work with
	void setBuffer(byte* input, size_t len)
	{
		start = ptr = input;
		end = start+len;
		usedBits = 0;
	}

	/// \brief
	/// Reads a bit-packed unsigned integer from the stream
	/// and returns it.  The given bitcount determines the
	/// number of bits to read.
	unsigned read_uint(unsigned short bitcount);

	/// \brief
	/// Reads a single bit off the stream
	/// and returns it.  
	bool read_bit();

	/// \brief
	/// Reads a bit-packed little-endian signed integer
	/// from the stream.  The given bitcount determines the
	/// number of bits to read.
	boost::int32_t read_sint(unsigned short bitcount);

	/// Read a byte as an unsigned int (aligned)
	boost::uint8_t  read_u8()
	{
		align();
		return *ptr++;
	}

	/// Read one bytes as a signed int (aligned)
    boost::int8_t read_s8()
	{
		return static_cast<boost::int8_t>(read_u8());
	}

	/// Read two bytes as an unsigned int (aligned)
	boost::uint16_t read_u16()
	{
		align();
		assert(ptr+2 < end);
		boost::uint16_t result = *ptr++;
		result |= *ptr++ << 8;
		return result ;
	}

	/// Read two bytes as a signed int (aligned)
	boost::int16_t	read_s16()
	{
		return static_cast<boost::int16_t>(read_u16());
	}

	/// Read four bytes as an unsigned int (aligned)
	boost::uint32_t read_u32()
	{
		align();
		assert(ptr+4 < end);
		boost::uint32_t result = *ptr++;
		result |= *ptr++ << 8;
		result |= *ptr++ << 16;
		result |= *ptr++ << 24;
		return(result);
	}

	/// Read four bytes as an signed int (aligned)
	boost::int32_t read_s32()
	{
		return static_cast<boost::int32_t>(read_u32());
	}

	/// \brief
	/// Discard any unused bit in the current byte
	/// and advance to next
	void align()
	{
		if ( usedBits ) advanceToNextByte();
	}

	/// Checks if the stream contains X bits
	bool gotBits(boost::uint32_t nbits)
	{
		boost::uint32_t gotbits = 8-usedBits +8*(end-ptr-1);
		if (gotbits > nbits) return true;
		else return false;
	}

private:

	void advanceToNextByte()
	{
		if ( ++ptr == end )
		{
			log_debug(_("Going round"));
			ptr=start;
		}
		usedBits=0;
	}

	/// Pointer to first byte
	const byte* start;

	/// Pointer to current byte
	const byte* ptr;

	/// Pointer to one past last byte
	const byte* end;

	/// Number of used bits in current byte
	unsigned usedBits;

};


}	// end namespace gnash


#endif // BITSREADER_H


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