/*************************************************************************** bitstream.h Helper classes for reading/writing at the bit level. **************************************************************************** Copyright Aaron Giles All rights reserved. Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met: * Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer. * Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution. * Neither the name 'MAME' nor the names of its contributors may be used to endorse or promote products derived from this software without specific prior written permission. THIS SOFTWARE IS PROVIDED BY AARON GILES ''AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL AARON GILES BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. ***************************************************************************/ #pragma once #ifndef __BITSTREAM_H__ #define __BITSTREAM_H__ #include "osdcore.h" //************************************************************************** // TYPE DEFINITIONS //************************************************************************** // helper class for reading from a bit buffer class bitstream_in { public: // construction/destruction bitstream_in(const void *src, UINT32 srclength); // getters bool overflow() const { return ((m_doffset - m_bits / 8) > m_dlength); } UINT32 read_offset() const; // operations UINT32 read(int numbits); UINT32 peek(int numbits); void remove(int numbits); UINT32 flush(); private: // internal state UINT32 m_buffer; // current bit accumulator int m_bits; // number of bits in the accumulator const UINT8 * m_read; // read pointer UINT32 m_doffset; // byte offset within the data UINT32 m_dlength; // length of the data }; // helper class for writing to a bit buffer class bitstream_out { public: // construction/destruction bitstream_out(void *dest, UINT32 destlength); // getters bool overflow() const { return (m_doffset > m_dlength); } // operations void write(UINT32 newbits, int numbits); UINT32 flush(); private: // internal state UINT32 m_buffer; // current bit accumulator int m_bits; // number of bits in the accumulator UINT8 * m_write; // write pointer UINT32 m_doffset; // byte offset within the data UINT32 m_dlength; // length of the data }; //************************************************************************** // INLINE FUNCTIONS //************************************************************************** //------------------------------------------------- // bitstream_in - constructor //------------------------------------------------- inline bitstream_in::bitstream_in(const void *src, UINT32 srclength) : m_buffer(0), m_bits(0), m_read(reinterpret_cast(src)), m_doffset(0), m_dlength(srclength) { } //------------------------------------------------- // peek - fetch the requested number of bits // but don't advance the input pointer //------------------------------------------------- inline UINT32 bitstream_in::peek(int numbits) { if (numbits == 0) return 0; // fetch data if we need more if (numbits > m_bits) { while (m_bits <= 24) { if (m_doffset < m_dlength) m_buffer |= m_read[m_doffset] << (24 - m_bits); m_doffset++; m_bits += 8; } } // return the data return m_buffer >> (32 - numbits); } //------------------------------------------------- // remove - advance the input pointer by the // specified number of bits //------------------------------------------------- inline void bitstream_in::remove(int numbits) { m_buffer <<= numbits; m_bits -= numbits; } //------------------------------------------------- // read - fetch the requested number of bits //------------------------------------------------- inline UINT32 bitstream_in::read(int numbits) { UINT32 result = peek(numbits); remove(numbits); return result; } //------------------------------------------------- // read_offset - return the current read offset //------------------------------------------------- inline UINT32 bitstream_in::read_offset() const { UINT32 result = m_doffset; int bits = m_bits; while (bits >= 8) { result--; bits -= 8; } return result; } //------------------------------------------------- // flush - flush to the nearest byte //------------------------------------------------- inline UINT32 bitstream_in::flush() { while (m_bits >= 8) { m_doffset--; m_bits -= 8; } m_bits = m_buffer = 0; return m_doffset; } //------------------------------------------------- // bitstream_out - constructor //------------------------------------------------- inline bitstream_out::bitstream_out(void *dest, UINT32 destlength) : m_buffer(0), m_bits(0), m_write(reinterpret_cast(dest)), m_doffset(0), m_dlength(destlength) { } //------------------------------------------------- // write - write the given number of bits to the // data stream //------------------------------------------------- inline void bitstream_out::write(UINT32 newbits, int numbits) { // flush the buffer if we're going to overflow it if (m_bits + numbits > 32) while (m_bits >= 8) { if (m_doffset < m_dlength) m_write[m_doffset] = m_buffer >> 24; m_doffset++; m_buffer <<= 8; m_bits -= 8; } // shift the bits to the top if (numbits == 0) newbits = 0; else newbits <<= 32 - numbits; // now shift it down to account for the number of bits we already have and OR them in m_buffer |= newbits >> m_bits; m_bits += numbits; } //------------------------------------------------- // flush - output remaining bits and return the // final output size in bytes //------------------------------------------------- inline UINT32 bitstream_out::flush() { while (m_bits > 0) { if (m_doffset < m_dlength) m_write[m_doffset] = m_buffer >> 24; m_doffset++; m_buffer <<= 8; m_bits -= 8; } m_bits = m_buffer = 0; return m_doffset; } #endif