83 lines
1.8 KiB
C++
83 lines
1.8 KiB
C++
/*
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* BitReader.h
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* -----------
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* Purpose: An extended FileReader to read bit-oriented rather than byte-oriented streams.
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* Notes : The current implementation can only read bit widths up to 32 bits, and it always
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* reads bits starting from the least significant bit, as this is all that is
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* required by the class users at the moment.
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* Authors: OpenMPT Devs
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* The OpenMPT source code is released under the BSD license. Read LICENSE for more details.
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*/
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#pragma once
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#include "openmpt/all/BuildSettings.hpp"
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#include "../common/FileReader.h"
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#include <stdexcept>
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#include "mpt/io/base.hpp"
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OPENMPT_NAMESPACE_BEGIN
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class BitReader : private FileReader
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{
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protected:
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off_t m_bufPos = 0, m_bufSize = 0;
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uint32 bitBuf = 0; // Current bit buffer
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int m_bitNum = 0; // Currently available number of bits
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std::byte buffer[mpt::IO::BUFFERSIZE_TINY]{};
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public:
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class eof : public std::range_error
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{
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public:
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eof() : std::range_error("Truncated bit buffer") { }
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};
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BitReader() : FileReader() { }
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BitReader(mpt::span<const std::byte> bytedata) : FileReader(bytedata) { }
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BitReader(const FileCursor &other) : FileReader(other) { }
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BitReader(FileCursor &&other) : FileReader(std::move(other)) { }
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off_t GetLength() const
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{
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return FileReader::GetLength();
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}
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off_t GetPosition() const
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{
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return FileReader::GetPosition() - m_bufSize + m_bufPos;
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}
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uint32 ReadBits(int numBits)
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{
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while(m_bitNum < numBits)
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{
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// Fetch more bits
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if(m_bufPos >= m_bufSize)
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{
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m_bufSize = ReadRaw(mpt::as_span(buffer)).size();
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m_bufPos = 0;
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if(!m_bufSize)
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{
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throw eof();
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}
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}
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bitBuf |= (static_cast<uint32>(buffer[m_bufPos++]) << m_bitNum);
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m_bitNum += 8;
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}
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uint32 v = bitBuf & ((1 << numBits) - 1);
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bitBuf >>= numBits;
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m_bitNum -= numBits;
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return v;
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}
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};
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OPENMPT_NAMESPACE_END
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