Common C++ classes and routines used by my applications such as argument parser, IO and conversion utilities
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#ifndef IOUTILITIES_BITREADER_H
#define IOUTILITIES_BITREADER_H
#include "../global.h"
#include <cstdint>
#include <ios>
#include <iostream>
#include <type_traits>
namespace CppUtilities {
class CPP_UTILITIES_EXPORT BitReader {
public:
BitReader(const char *buffer, std::size_t bufferSize);
BitReader(const char *buffer, const char *end);
template <typename intType> intType readBits(std::uint8_t bitCount);
std::uint8_t readBit();
template <typename intType> intType readUnsignedExpGolombCodedBits();
template <typename intType> intType readSignedExpGolombCodedBits();
template <typename intType> intType showBits(std::uint8_t bitCount);
void skipBits(std::size_t bitCount);
void align();
std::size_t bitsAvailable();
void reset(const char *buffer, std::size_t bufferSize);
void reset(const char *buffer, const char *end);
private:
const std::uint8_t *m_buffer;
const std::uint8_t *m_end;
std::uint8_t m_bitsAvail;
};
/*!
* \brief Constructs a new BitReader.
* \remarks
* - Does not take ownership over the specified \a buffer.
* - bufferSize must be equal or greater than 1.
*/
inline BitReader::BitReader(const char *buffer, std::size_t bufferSize)
: BitReader(buffer, buffer + bufferSize)
{
}
/*!
* \brief Constructs a new BitReader.
* \remarks
* - Does not take ownership over the specified \a buffer.
* - \a end must be greater than \a buffer.
*/
inline BitReader::BitReader(const char *buffer, const char *end)
: m_buffer(reinterpret_cast<const std::uint8_t *>(buffer))
, m_end(reinterpret_cast<const std::uint8_t *>(end))
, m_bitsAvail(8)
{
}
/*!
* \brief Reads the specified number of bits from the buffer advancing the current position by \a bitCount bits.
* \param bitCount Specifies the number of bits read.
* \tparam intType Specifies the type of the returned value.
* \remarks Does not check whether intType is big enough to hold result.
* \throws Throws ios_base::failure if the end of the buffer is exceeded.
* The reader becomes invalid in that case.
*/
template <typename intType> intType BitReader::readBits(std::uint8_t bitCount)
{
intType val = 0;
for (std::uint8_t readAtOnce; bitCount; bitCount -= readAtOnce) {
if (!m_bitsAvail) {
if (++m_buffer >= m_end) {
throw std::ios_base::failure("end of buffer exceeded");
}
m_bitsAvail = 8;
}
readAtOnce = std::min(bitCount, m_bitsAvail);
val = static_cast<intType>(
(val << readAtOnce) | static_cast<intType>(((*m_buffer) >> (m_bitsAvail -= readAtOnce)) & (0xFF >> (0x08 - readAtOnce))));
}
return val;
}
/*!
* \brief Reads the one bit from the buffer advancing the current position by one bit.
* \throws Throws ios_base::failure if the end of the buffer is exceeded.
* The reader becomes invalid in that case.
*/
inline std::uint8_t BitReader::readBit()
{
return readBits<std::uint8_t>(1) == 1;
}
/*!
* \brief Reads "Exp-Golomb coded" bits (unsigned).
* \tparam intType Specifies the type of the returned value.
* \remarks Does not check whether intType is big enough to hold result.
* \throws Throws ios_base::failure if the end of the buffer is exceeded.
* The reader becomes invalid in that case.
* \sa https://en.wikipedia.org/wiki/Exponential-Golomb_coding
*/
template <typename intType> intType BitReader::readUnsignedExpGolombCodedBits()
{
std::uint8_t count = 0;
while (!readBit()) {
++count;
}
return count ? static_cast<intType>(((1 << count) | readBits<intType>(count)) - 1) : 0;
}
/*!
* \brief Reads "Exp-Golomb coded" bits (signed).
* \tparam intType Specifies the type of the returned value which should be signed (obviously).
* \remarks Does not check whether intType is big enough to hold result.
* \throws Throws ios_base::failure if the end of the buffer is exceeded.
* The reader becomes invalid in that case.
* \sa https://en.wikipedia.org/wiki/Exponential-Golomb_coding
*/
template <typename intType> intType BitReader::readSignedExpGolombCodedBits()
{
auto value = readUnsignedExpGolombCodedBits<typename std::make_unsigned<intType>::type>();
return (value % 2) ? static_cast<intType>((value + 1) / 2) : (-static_cast<intType>(value / 2));
}
/*!
* \brief Reads the specified number of bits from the buffer without advancing the current position.
*/
template <typename intType> intType BitReader::showBits(std::uint8_t bitCount)
{
auto tmp = *this;
return tmp.readBits<intType>(bitCount);
}
/*!
* \brief Returns the number of bits which are still available to read.
*/
inline std::size_t BitReader::bitsAvailable()
{
return m_buffer != m_end ? static_cast<std::size_t>(((m_end - m_buffer - 1) * 8) + m_bitsAvail) : static_cast<std::size_t>(0);
}
/*!
* \brief Resets the reader.
* \remarks
* - Does not take ownership over the specified \a buffer.
* - bufferSize must be equal or greater than 1.
*/
inline void BitReader::reset(const char *buffer, std::size_t bufferSize)
{
m_buffer = reinterpret_cast<const std::uint8_t *>(buffer);
m_end = reinterpret_cast<const std::uint8_t *>(buffer + bufferSize);
m_bitsAvail = 8;
}
/*!
* \brief Resets the reader.
* \remarks
* - Does not take ownership over the specified \a buffer.
* - \a end must be greater than \a buffer.
*/
inline void BitReader::reset(const char *buffer, const char *end)
{
m_buffer = reinterpret_cast<const std::uint8_t *>(buffer);
m_end = reinterpret_cast<const std::uint8_t *>(end);
m_bitsAvail = 8;
}
/*!
* \brief Re-establishes alignment.
*/
inline void BitReader::align()
{
skipBits(m_bitsAvail);
}
} // namespace CppUtilities
#endif // IOUTILITIES_BITREADER_H