core/src/fxcodec/jbig2/JBig2_ArithDecoder.cpp

// Copyright 2014 PDFium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

// Original code copyright 2014 Foxit Software Inc. http://www.foxitsoftware.com

#include "JBig2_ArithDecoder.h"

#include "../../../include/fxcrt/fx_basic.h"
#include "JBig2_BitStream.h"
#include "JBig2_Define.h"

namespace {

struct JBig2ArithQe {
  unsigned int Qe;
  unsigned int NMPS;
  unsigned int NLPS;
  unsigned int nSwitch;
};

const JBig2ArithQe kQeTable[] = {
    // Stupid hack to keep clang-format from reformatting this badly.
    {0x5601, 1, 1, 1},
    {0x3401, 2, 6, 0},
    {0x1801, 3, 9, 0},
    {0x0AC1, 4, 12, 0},
    {0x0521, 5, 29, 0},
    {0x0221, 38, 33, 0},
    {0x5601, 7, 6, 1},
    {0x5401, 8, 14, 0},
    {0x4801, 9, 14, 0},
    {0x3801, 10, 14, 0},
    {0x3001, 11, 17, 0},
    {0x2401, 12, 18, 0},
    {0x1C01, 13, 20, 0},
    {0x1601, 29, 21, 0},
    {0x5601, 15, 14, 1},
    {0x5401, 16, 14, 0},
    {0x5101, 17, 15, 0},
    {0x4801, 18, 16, 0},
    {0x3801, 19, 17, 0},
    {0x3401, 20, 18, 0},
    {0x3001, 21, 19, 0},
    {0x2801, 22, 19, 0},
    {0x2401, 23, 20, 0},
    {0x2201, 24, 21, 0},
    {0x1C01, 25, 22, 0},
    {0x1801, 26, 23, 0},
    {0x1601, 27, 24, 0},
    {0x1401, 28, 25, 0},
    {0x1201, 29, 26, 0},
    {0x1101, 30, 27, 0},
    {0x0AC1, 31, 28, 0},
    {0x09C1, 32, 29, 0},
    {0x08A1, 33, 30, 0},
    {0x0521, 34, 31, 0},
    {0x0441, 35, 32, 0},
    {0x02A1, 36, 33, 0},
    {0x0221, 37, 34, 0},
    {0x0141, 38, 35, 0},
    {0x0111, 39, 36, 0},
    {0x0085, 40, 37, 0},
    {0x0049, 41, 38, 0},
    {0x0025, 42, 39, 0},
    {0x0015, 43, 40, 0},
    {0x0009, 44, 41, 0},
    {0x0005, 45, 42, 0},
    {0x0001, 45, 43, 0},
    {0x5601, 46, 46, 0}};

}  // namespace

CJBig2_ArithDecoder::CJBig2_ArithDecoder(CJBig2_BitStream* pStream) {
  m_pStream = pStream;
  INITDEC();
}

CJBig2_ArithDecoder::~CJBig2_ArithDecoder() {
}

int CJBig2_ArithDecoder::DECODE(JBig2ArithCtx* pCX) {
  if (!pCX || pCX->I >= FX_ArraySize(kQeTable)) {
    return 0;
  }

  int D;
  const JBig2ArithQe* qe = &kQeTable[pCX->I];
  A = A - qe->Qe;
  if ((C >> 16) < A) {
    if (A & 0x8000) {
      D = pCX->MPS;
    } else {
      if (A < qe->Qe) {
        D = 1 - pCX->MPS;
        if (qe->nSwitch == 1) {
          pCX->MPS = 1 - pCX->MPS;
        }
        pCX->I = qe->NLPS;
      } else {
        D = pCX->MPS;
        pCX->I = qe->NMPS;
      }
      do {
        if (CT == 0) {
          BYTEIN();
        }
        A <<= 1;
        C <<= 1;
        CT--;
      } while ((A & 0x8000) == 0);
    }
  } else {
    C -= A << 16;
    if (A < qe->Qe) {
      A = qe->Qe;
      D = pCX->MPS;
      pCX->I = qe->NMPS;
    } else {
      A = qe->Qe;
      D = 1 - pCX->MPS;
      if (qe->nSwitch == 1) {
        pCX->MPS = 1 - pCX->MPS;
      }
      pCX->I = qe->NLPS;
    }
    do {
      if (CT == 0) {
        BYTEIN();
      }
      A <<= 1;
      C <<= 1;
      CT--;
    } while ((A & 0x8000) == 0);
  }
  return D;
}

void CJBig2_ArithDecoder::INITDEC() {
  B = m_pStream->getCurByte_arith();
  C = (B ^ 0xff) << 16;
  BYTEIN();
  C = C << 7;
  CT = CT - 7;
  A = 0x8000;
}

void CJBig2_ArithDecoder::BYTEIN() {
  unsigned char B1;
  if (B == 0xff) {
    B1 = m_pStream->getNextByte_arith();
    if (B1 > 0x8f) {
      CT = 8;
    } else {
      m_pStream->incByteIdx();
      B = B1;
      C = C + 0xfe00 - (B << 9);
      CT = 7;
    }
  } else {
    m_pStream->incByteIdx();
    B = m_pStream->getCurByte_arith();
    C = C + 0xff00 - (B << 8);
    CT = 8;
  }
}