83 lines
1.8 KiB
C
83 lines
1.8 KiB
C
|
/*
|
||
|
|
* 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
|