PDF4QT/PdfForQtLib/sources/pdfutils.cpp

//    Copyright (C) 2019 Jakub Melka
//
//    This file is part of PdfForQt.
//
//    PdfForQt is free software: you can redistribute it and/or modify
//    it under the terms of the GNU Lesser General Public License as published by
//    the Free Software Foundation, either version 3 of the License, or
//    (at your option) any later version.
//
//    PdfForQt is distributed in the hope that it will be useful,
//    but WITHOUT ANY WARRANTY; without even the implied warranty of
//    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
//    GNU Lesser General Public License for more details.
//
//    You should have received a copy of the GNU Lesser General Public License
//    along with PDFForQt.  If not, see <https://www.gnu.org/licenses/>.

#include "pdfutils.h"
#include "pdfexception.h"

namespace pdf
{

PDFBitReader::PDFBitReader(const QByteArray* stream, Value bitsPerComponent) :
    m_stream(stream),
    m_position(0),
    m_bitsPerComponent(bitsPerComponent),
    m_maximalValue((static_cast<Value>(1) << m_bitsPerComponent) - static_cast<Value>(1)),
    m_buffer(0),
    m_bitsInBuffer(0)
{
    // We need reserve, so we allow number of length of component as 1-56 bits.
    Q_ASSERT(bitsPerComponent > 0);
    Q_ASSERT(bitsPerComponent < 56);
}

PDFBitReader::Value PDFBitReader::read(PDFBitReader::Value bits)
{
    while (m_bitsInBuffer < bits)
    {
        if (m_position < m_stream->size())
        {
            uint8_t currentByte = static_cast<uint8_t>((*m_stream)[m_position++]);
            m_buffer = (m_buffer << 8) | currentByte;
            m_bitsInBuffer += 8;
        }
        else
        {
            throw PDFException(PDFTranslationContext::tr("Not enough data to read %1-bit value.").arg(bits));
        }
    }

    // Now we have enough bits to read the data
    Value value = (m_buffer >> (m_bitsInBuffer - bits)) & ((static_cast<Value>(1) << bits) - static_cast<Value>(1));
    m_bitsInBuffer -= bits;
    return value;
}

PDFBitReader::Value PDFBitReader::look(Value bits) const
{
    PDFBitReader temp(*this);

    Value result = 0;
    for (Value i = 0; i < bits; ++i)
    {
        if (!temp.isAtEnd())
        {
            result = (result << 1) | temp.read(1);
        }
        else
        {
            result = (result << 1);
        }
    }

    return result;
}

void PDFBitReader::seek(qint64 position)
{
    if (position <= m_stream->size())
    {
        m_position = position;
        m_buffer = 0;
        m_bitsInBuffer = 0;
    }
    else
    {
        throw PDFException(PDFTranslationContext::tr("Can't seek to position %1.").arg(position));
    }
}

void PDFBitReader::skipBytes(Value bytes)
{
    // Jakub Melka: if we are lucky, then we just seek to the new position
    if (m_bitsInBuffer == 0)
    {
        seek(m_position + bytes);
    }
    else
    {
        for (Value i = 0; i < bytes; ++i)
        {
            read(8);
        }
    }
}

void PDFBitReader::alignToBytes()
{
    const Value remainder = m_bitsInBuffer % 8;
    if (remainder > 0)
    {
        read(remainder);
    }
}

bool PDFBitReader::isAtEnd() const
{
    return (m_position >= m_stream->size()) && m_bitsInBuffer == 0;
}

int32_t PDFBitReader::readSignedInt()
{
    const uint32_t value = read(32);
    return *reinterpret_cast<const int32_t*>(&value);
}

int8_t PDFBitReader::readSignedByte()
{
    const uint8_t value = read(8);
    return *reinterpret_cast<const int8_t*>(&value);
}

PDFBitWriter::PDFBitWriter(Value bitsPerComponent) :
    m_bitsPerComponent(bitsPerComponent),
    m_mask((static_cast<Value>(1) << m_bitsPerComponent) - static_cast<Value>(1)),
    m_buffer(0),
    m_bitsInBuffer(0)
{

}

void PDFBitWriter::write(Value value)
{
    m_buffer = (m_buffer << m_bitsPerComponent) | (value & m_mask);
    m_bitsInBuffer += m_bitsPerComponent;

    flush(false);
}

void PDFBitWriter::flush(bool alignToByteBoundary)
{
    if (m_bitsInBuffer >= 8)
    {
        Value remainder = m_bitsInBuffer % 8;
        Value alignedBuffer = m_buffer >> remainder;
        Value bitsToWrite = m_bitsInBuffer - remainder;
        Value bytesToWrite = bitsToWrite / 8;

        for (Value byteIndex = 0; byteIndex < bytesToWrite; ++byteIndex)
        {
            const Value shift = (bytesToWrite - 1 - byteIndex) * 8;
            m_outputByteArray.push_back(static_cast<const char>(static_cast<uint8_t>((alignedBuffer >> shift) & 0xFF)));
        }

        m_bitsInBuffer = remainder;
    }

    if (alignToByteBoundary && m_bitsInBuffer > 0)
    {
        Value missingBits = 8 - m_bitsInBuffer % 8;
        m_buffer = m_buffer << missingBits;
        m_bitsInBuffer += missingBits;
        flush(false);
    }
}

}   // namespace pdf