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