mirror of
https://github.com/libretro/scummvm.git
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326 lines
8.7 KiB
C++
326 lines
8.7 KiB
C++
/* ScummVM - Graphic Adventure Engine
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*
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* ScummVM is the legal property of its developers, whose names
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* are too numerous to list here. Please refer to the COPYRIGHT
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* file distributed with this source distribution.
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public License
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* as published by the Free Software Foundation; either version 2
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* of the License, or (at your option) any later version.
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, write to the Free Software
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* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
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*
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*/
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// Based on eos' BitStream implementation
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#ifndef COMMON_BITSTREAM_H
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#define COMMON_BITSTREAM_H
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#include "common/scummsys.h"
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#include "common/textconsole.h"
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#include "common/stream.h"
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namespace Common {
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/** A bit stream. */
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class BitStream {
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public:
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virtual ~BitStream() {
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}
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/** Return the stream position in bits. */
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virtual uint32 pos() const = 0;
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/** Return the stream size in bits. */
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virtual uint32 size() const = 0;
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/** Has the end of the stream been reached? */
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virtual bool eos() const = 0;
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/** Rewind the bit stream back to the start. */
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virtual void rewind() = 0;
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/** Skip the specified amount of bits. */
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virtual void skip(uint32 n) = 0;
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/** Read a bit from the bit stream. */
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virtual uint32 getBit() = 0;
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/** Read a multi-bit value from the bit stream. */
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virtual uint32 getBits(uint8 n) = 0;
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/** Read a bit from the bit stream, without changing the stream's position. */
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virtual uint32 peekBit() = 0;
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/** Read a multi-bit value from the bit stream, without changing the stream's position. */
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virtual uint32 peekBits(uint8 n) = 0;
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/** Add a bit to the value x, making it an n+1-bit value. */
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virtual void addBit(uint32 &x, uint32 n) = 0;
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protected:
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BitStream() {
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}
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};
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/**
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* A template implementing a bit stream for different data memory layouts.
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*
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* Such a bit stream reads valueBits-wide values from the data stream and
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* gives access to their bits, one at a time.
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*
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* For example, a bit stream with the layout parameters 32, true, false
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* for valueBits, isLE and isMSB2LSB, reads 32bit little-endian values
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* from the data stream and hands out the bits in the order of LSB to MSB.
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*/
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template<int valueBits, bool isLE, bool isMSB2LSB>
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class BitStreamImpl : public BitStream {
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private:
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SeekableReadStream *_stream; ///< The input stream.
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bool _disposeAfterUse; ///< Should we delete the stream on destruction?
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uint32 _value; ///< Current value.
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uint8 _inValue; ///< Position within the current value.
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/** Read a data value. */
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inline uint32 readData() {
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if (isLE) {
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if (valueBits == 8)
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return _stream->readByte();
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if (valueBits == 16)
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return _stream->readUint16LE();
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if (valueBits == 32)
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return _stream->readUint32LE();
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} else {
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if (valueBits == 8)
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return _stream->readByte();
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if (valueBits == 16)
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return _stream->readUint16BE();
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if (valueBits == 32)
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return _stream->readUint32BE();
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}
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assert(false);
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return 0;
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}
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/** Read the next data value. */
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inline void readValue() {
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if ((size() - pos()) < valueBits)
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error("BitStreamImpl::readValue(): End of bit stream reached");
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_value = readData();
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if (_stream->err() || _stream->eos())
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error("BitStreamImpl::readValue(): Read error");
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// If we're reading the bits MSB first, we need to shift the value to that position
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if (isMSB2LSB)
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_value <<= 32 - valueBits;
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}
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public:
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/** Create a bit stream using this input data stream and optionally delete it on destruction. */
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BitStreamImpl(SeekableReadStream *stream, bool disposeAfterUse = false) :
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_stream(stream), _disposeAfterUse(disposeAfterUse), _value(0), _inValue(0) {
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if ((valueBits != 8) && (valueBits != 16) && (valueBits != 32))
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error("BitStreamImpl: Invalid memory layout %d, %d, %d", valueBits, isLE, isMSB2LSB);
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}
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/** Create a bit stream using this input data stream. */
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BitStreamImpl(SeekableReadStream &stream) :
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_stream(&stream), _disposeAfterUse(false), _value(0), _inValue(0) {
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if ((valueBits != 8) && (valueBits != 16) && (valueBits != 32))
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error("BitStreamImpl: Invalid memory layout %d, %d, %d", valueBits, isLE, isMSB2LSB);
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}
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~BitStreamImpl() {
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if (_disposeAfterUse)
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delete _stream;
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}
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/** Read a bit from the bit stream. */
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uint32 getBit() {
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// Check if we need the next value
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if (_inValue == 0)
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readValue();
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// Get the current bit
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int b = 0;
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if (isMSB2LSB)
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b = ((_value & 0x80000000) == 0) ? 0 : 1;
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else
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b = ((_value & 1) == 0) ? 0 : 1;
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// Shift to the next bit
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if (isMSB2LSB)
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_value <<= 1;
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else
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_value >>= 1;
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// Increase the position within the current value
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_inValue = (_inValue + 1) % valueBits;
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return b;
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}
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/**
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* Read a multi-bit value from the bit stream.
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*
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* The value is read as if just taken as a whole from the bitstream.
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*
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* For example:
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* Reading a 4-bit value from an 8-bit bitstream with the contents 01010011:
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* If the bitstream is MSB2LSB, the 4-bit value would be 0101.
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* If the bitstream is LSB2MSB, the 4-bit value would be 0011.
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*/
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uint32 getBits(uint8 n) {
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if (n == 0)
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return 0;
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if (n > 32)
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error("BitStreamImpl::getBits(): Too many bits requested to be read");
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// Read the number of bits
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uint32 v = 0;
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if (isMSB2LSB) {
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while (n-- > 0)
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v = (v << 1) | getBit();
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} else {
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for (uint32 i = 0; i < n; i++)
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v = (v >> 1) | (((uint32) getBit()) << 31);
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v >>= (32 - n);
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}
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return v;
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}
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/** Read a bit from the bit stream, without changing the stream's position. */
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uint32 peekBit() {
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uint32 value = _value;
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uint8 inValue = _inValue;
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uint32 curPos = _stream->pos();
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uint32 v = getBit();
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_stream->seek(curPos);
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_inValue = inValue;
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_value = value;
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return v;
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}
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/**
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* Read a multi-bit value from the bit stream, without changing the stream's position.
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*
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* The bit order is the same as in getBits().
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*/
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uint32 peekBits(uint8 n) {
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uint32 value = _value;
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uint8 inValue = _inValue;
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uint32 curPos = _stream->pos();
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uint32 v = getBits(n);
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_stream->seek(curPos);
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_inValue = inValue;
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_value = value;
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return v;
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}
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/**
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* Add a bit to the value x, making it an n+1-bit value.
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*
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* The current value is shifted and the bit is added to the
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* appropriate place, dependant on the stream's bitorder.
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*
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* For example:
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* A bit y is added to the value 00001100 with size 4.
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* If the stream's bitorder is MSB2LSB, the resulting value is 0001100y.
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* If the stream's bitorder is LSB2MSB, the resulting value is 000y1100.
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*/
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void addBit(uint32 &x, uint32 n) {
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if (n >= 32)
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error("BitStreamImpl::addBit(): Too many bits requested to be read");
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if (isMSB2LSB)
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x = (x << 1) | getBit();
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else
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x = (x & ~(1 << n)) | (getBit() << n);
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}
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/** Rewind the bit stream back to the start. */
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void rewind() {
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_stream->seek(0);
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_value = 0;
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_inValue = 0;
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}
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/** Skip the specified amount of bits. */
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void skip(uint32 n) {
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while (n-- > 0)
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getBit();
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}
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/** Return the stream position in bits. */
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uint32 pos() const {
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if (_stream->pos() == 0)
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return 0;
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uint32 p = (_inValue == 0) ? _stream->pos() : ((_stream->pos() - 1) & ~((uint32) ((valueBits >> 3) - 1)));
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return p * 8 + _inValue;
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}
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/** Return the stream size in bits. */
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uint32 size() const {
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return (_stream->size() & ~((uint32) ((valueBits >> 3) - 1))) * 8;
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}
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bool eos() const {
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return _stream->eos() || (pos() >= size());
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}
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};
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// typedefs for various memory layouts.
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/** 8-bit data, MSB to LSB. */
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typedef BitStreamImpl<8, false, true > BitStream8MSB;
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/** 8-bit data, LSB to MSB. */
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typedef BitStreamImpl<8, false, false> BitStream8LSB;
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/** 16-bit little-endian data, MSB to LSB. */
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typedef BitStreamImpl<16, true , true > BitStream16LEMSB;
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/** 16-bit little-endian data, LSB to MSB. */
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typedef BitStreamImpl<16, true , false> BitStream16LELSB;
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/** 16-bit big-endian data, MSB to LSB. */
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typedef BitStreamImpl<16, false, true > BitStream16BEMSB;
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/** 16-bit big-endian data, LSB to MSB. */
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typedef BitStreamImpl<16, false, false> BitStream16BELSB;
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/** 32-bit little-endian data, MSB to LSB. */
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typedef BitStreamImpl<32, true , true > BitStream32LEMSB;
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/** 32-bit little-endian data, LSB to MSB. */
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typedef BitStreamImpl<32, true , false> BitStream32LELSB;
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/** 32-bit big-endian data, MSB to LSB. */
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typedef BitStreamImpl<32, false, true > BitStream32BEMSB;
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/** 32-bit big-endian data, LSB to MSB. */
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typedef BitStreamImpl<32, false, false> BitStream32BELSB;
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} // End of namespace Common
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#endif // COMMON_BITSTREAM_H
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