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Diffstat (limited to 'common/bitstream.h')
| -rw-r--r-- | common/bitstream.h | 173 |
1 files changed, 173 insertions, 0 deletions
diff --git a/common/bitstream.h b/common/bitstream.h new file mode 100644 index 0000000000..7be0dccf45 --- /dev/null +++ b/common/bitstream.h @@ -0,0 +1,173 @@ +/* ScummVM - Graphic Adventure Engine + * + * ScummVM is the legal property of its developers, whose names + * are too numerous to list here. Please refer to the COPYRIGHT + * file distributed with this source distribution. + * + * 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 2 + * 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 Street, Fifth Floor, Boston, MA 02110-1301, USA. + * + */ + +// Based on eos' BitStream implementation + +#ifndef COMMON_BITSTREAM_H +#define COMMON_BITSTREAM_H + +#include "common/scummsys.h" + +namespace Common { + +class SeekableReadStream; + +/** + * A bit stream, giving access to data one bit at a time. + * + * Used in engines: + * - scumm + */ +class BitStream { +public: + BitStream(); + virtual ~BitStream(); + + /** Read a bit from the bitstream. */ + virtual uint32 getBit() = 0; + + /** Read a number of bits, creating a multi-bit value. */ + virtual uint32 getBits(uint32 n) = 0; + + /** Add more bits, creating a multi-bit value in stages. */ + virtual void addBit(uint32 &x, uint32 n) = 0; + + /** Skip a number of bits. */ + void skip(uint32 n); + + /** Get the current position, in bits. */ + virtual uint32 pos() const = 0; + /** Return the number of bits in the stream. */ + virtual uint32 size() const = 0; +}; + +/** + * A big-endian bit stream. + * + * The input data is read one byte at a time. Their bits are handed out + * in the order of MSB to LSB. When all 8 bits of a byte have been consumed, + * another input data byte is read. + */ +class BitStreamBE : public BitStream { +public: + /** + * Create a big endian bit stream. + * + * Reads and copies bitCount bits from the provided stream. + * Ownership of the stream is not transferred. + */ + BitStreamBE(SeekableReadStream &stream, uint32 bitCount); + + /** + * Create a big endian bit stream. + * + * Reads and copies bitCount bits from the provided data. + * Ownership of the data is not transferred. + */ + BitStreamBE(const byte *data, uint32 bitCount); + + ~BitStreamBE(); + + uint32 getBit(); + + /** + * Read a number of bits, creating a multi-bit value. + * + * The bits are read one at a time, in the order MSB to LSB and + * or'd together to create a multi-bit value. + */ + uint32 getBits(uint32 n); + + /** + * Add more bits, creating a multi-bit value in stages. + * + * Shifts in n new bits into the value x, in the order of MSB to LSB. + */ + void addBit(uint32 &x, uint32 n); + + uint32 pos() const; + uint32 size() const; + +private: + SeekableReadStream *_stream; + + byte _value; ///< Current byte. + uint8 _inValue; ///< Position within the current byte. +}; + +/** + * A little-endian bit stream, reading 32bit values at a time. + * + * The input data is read one little-endian uint32 at a time. Their bits are + * handed out in the order of LSB to MSB. When all 8 bits of a byte have been + * consumed, another little-endian input data uint32 is read. + */ +class BitStream32LE : public BitStream { +public: + /** + * Create a little-endian bit stream. + * + * Reads and copies bitCount bits from the provided stream. + * Ownership of the stream is not transferred. + */ + BitStream32LE(SeekableReadStream &stream, uint32 bitCount); + + /** + * Create a little-endian bit stream. + * + * Reads and copies bitCount bits from the provided data. + * Ownership of the data is not transferred. + */ + BitStream32LE(const byte *data, uint32 bitCount); + + ~BitStream32LE(); + + uint32 getBit(); + + /** + * Read a number of bits, creating a multi-bit value. + * + * The bits are read one at a time, in the order LSB to MSB and + * or'd together to create a multi-bit value. + */ + uint32 getBits(uint32 n); + + /** + * Add more bits, creating a multi-bit value in stages. + * + * Shifts in n new bits into the value x, in the order of LSB to MSB. + */ + void addBit(uint32 &x, uint32 n); + + uint32 pos() const; + uint32 size() const; + +private: + SeekableReadStream *_stream; + + uint32 _value; ///< Current 32bit value. + uint8 _inValue; ///< Position within the current 32bit value. +}; + +} // End of namespace Common + +#endif // COMMON_BITSTREAM_H |