JBIG2 - arithmetic decoder

PdfForQtLib/sources/pdfjbig2decoder.h

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+//    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/>.
+
+#ifndef PDFJBIG2DECODER_H
+#define PDFJBIG2DECODER_H
+
+#include "pdfutils.h"
+
+namespace pdf
+{
+
+/// Arithmetic decoder state for JBIG2 data streams. It contains state for context,
+/// state is stored as 8-bit value, where only 7 bits are used. 6 bits are used
+/// to store Qe value index (current row in the table, number 0-46), and lowest 1 bit
+/// is used to store current MPS value (most probable symbol - 0/1).
+class PDFJBIG2ArithmeticDecoderState
+{
+public:
+    explicit inline PDFJBIG2ArithmeticDecoderState(size_t size) :
+        m_state(size, 0)
+    {
+
+    }
+
+    /// Returns row index to Qe value table, according to document ISO/IEC 14492:2001,
+    /// annex E, table E.1 (Qe values and probability estimation process).
+    inline uint8_t getQeRowIndex(size_t context) const
+    {
+        Q_ASSERT(context < m_state.size());
+        return m_state[context] >> 1;
+    }
+
+    /// Returns current bit value of MPS (most probable symbol)
+    inline uint8_t getMPS(size_t context) const
+    {
+        Q_ASSERT(context < m_state.size());
+        return m_state[context] & 0x1;
+    }
+
+    /// Sets current row index to Qe value table, at given context, and also MPS bit value
+    /// (most probable symbol).
+    inline void setQeRowIndexAndMPS(size_t context, uint8_t QeRowIndex, uint8_t MPS)
+    {
+        Q_ASSERT(context < m_state.size());
+        Q_ASSERT(MPS < 2);
+        m_state[context] = (QeRowIndex << 1) + MPS;
+    }
+
+private:
+    std::vector<uint8_t> m_state;
+};
+
+/// Arithmetic decoder for JBIG2 data streams. This arithmetic decoder is implementation
+/// of decoder described in document ISO/IEC 14492:2001, T.88, annex G (arithmetic decoding
+/// procedure). It uses 32-bit fixed point arithmetic instead of 16-bit fixed point
+/// arithmetic described in the specification (it is much faster).
+class PDFJBIG2ArithmeticDecoder
+{
+public:
+    explicit inline PDFJBIG2ArithmeticDecoder() :
+        m_c(0),
+        m_a(0),
+        m_ct(0),
+        m_reader(nullptr)
+    {
+
+    }
+
+    void initialize() { perform_INITDEC(); }
+
+private:
+    /// Performs INITDEC operation as described in the specification
+    void perform_INITDEC();
+
+    /// Performs BYTEIN operation as described in the specification
+    void perform_BYTEIN();
+
+    /// Performs DECODE operation as described in the specification
+    /// \param context Context index
+    /// \param state State of the arithmetic decoder
+    /// \returns Single decoded bit (lowest bit, other bits are zero)
+    uint32_t perform_DECODE(size_t context, PDFJBIG2ArithmeticDecoderState* state);
+
+    /// This is 32 bit register consisting of two 16-bit subregisters - "c_high" and "c_low", as
+    /// it is in specification. But we can work with it as 32 bit register (if we adjust some
+    /// operations and fixed point arithmetic).
+    uint32_t m_c;
+
+    /// This is 32 bit register for interval range. In the specification, it is 16-bit register,
+    /// but we use 32-bit fixed point arithmetic instead of 16-bit fixed point arithmetic.
+    uint32_t m_a;
+
+    /// Number of current unprocessed bits.
+    uint32_t m_ct;
+
+    /// Data source to read from
+    PDFBitReader* m_reader;
+};
+
+class PDFJBIG2Decoder
+{
+public:
+    PDFJBIG2Decoder();
+};
+
+}   // namespace pdf
+
+#endif // PDFJBIG2DECODER_H