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      1 // Copyright 2014 PDFium Authors. All rights reserved.
      2 // Use of this source code is governed by a BSD-style license that can be
      3 // found in the LICENSE file.
      4 
      5 // Original code copyright 2014 Foxit Software Inc. http://www.foxitsoftware.com
      6 
      7 #ifndef _JBIG2_ARITHMETIC_DECODER_H_
      8 #define _JBIG2_ARITHMETIC_DECODER_H_
      9 #include "JBig2_Define.h"
     10 #include "JBig2_BitStream.h"
     11 #include "JBig2_ArithQe.h"
     12 typedef struct {
     13     unsigned int MPS;
     14     unsigned int I;
     15 } JBig2ArithCtx;
     16 class CJBig2_ArithDecoder : public CJBig2_Object
     17 {
     18 public:
     19 
     20     CJBig2_ArithDecoder(CJBig2_BitStream *pStream);
     21 
     22     ~CJBig2_ArithDecoder();
     23 
     24     int DECODE(JBig2ArithCtx *pCX);
     25 private:
     26 
     27     void INITDEC();
     28 
     29     void BYTEIN();
     30     unsigned char B;
     31     unsigned int C;
     32     unsigned int A;
     33     unsigned int CT;
     34     CJBig2_BitStream *m_pStream;
     35 };
     36 inline CJBig2_ArithDecoder::CJBig2_ArithDecoder(CJBig2_BitStream *pStream)
     37 {
     38     m_pStream = pStream;
     39     INITDEC();
     40 }
     41 inline CJBig2_ArithDecoder::~CJBig2_ArithDecoder()
     42 {
     43 }
     44 inline void CJBig2_ArithDecoder::INITDEC()
     45 {
     46     B = m_pStream->getCurByte_arith();
     47     C = (B ^ 0xff) << 16;;
     48     BYTEIN();
     49     C = C << 7;
     50     CT = CT - 7;
     51     A = 0x8000;
     52 }
     53 inline void CJBig2_ArithDecoder::BYTEIN()
     54 {
     55     unsigned char B1;
     56     if(B == 0xff) {
     57         B1 = m_pStream->getNextByte_arith();
     58         if(B1 > 0x8f) {
     59             CT = 8;
     60         } else {
     61             m_pStream->incByteIdx();
     62             B = B1;
     63             C = C + 0xfe00 - (B << 9);
     64             CT = 7;
     65         }
     66     } else {
     67         m_pStream->incByteIdx();
     68         B = m_pStream->getCurByte_arith();
     69         C = C + 0xff00 - (B << 8);
     70         CT = 8;
     71     }
     72 }
     73 inline int CJBig2_ArithDecoder::DECODE(JBig2ArithCtx *pCX)
     74 {
     75     int D;
     76     const JBig2ArithQe * qe = &QeTable[pCX->I];
     77     A = A - qe->Qe;
     78     if((C >> 16) < A) {
     79         if(A & 0x8000) {
     80             D = pCX->MPS;
     81         } else {
     82             if(A < qe->Qe) {
     83                 D = 1 - pCX->MPS;
     84                 if(qe->nSwitch == 1) {
     85                     pCX->MPS = 1 - pCX->MPS;
     86                 }
     87                 pCX->I = qe->NLPS;
     88             } else {
     89                 D = pCX->MPS;
     90                 pCX->I = qe->NMPS;
     91             }
     92             do {
     93                 if (CT == 0) {
     94                     BYTEIN();
     95                 }
     96                 A <<= 1;
     97                 C <<= 1;
     98                 CT--;
     99             } while ((A & 0x8000) == 0);
    100         }
    101     } else {
    102         C -= A << 16;
    103         if(A < qe->Qe) {
    104             A = qe->Qe;
    105             D = pCX->MPS;
    106             pCX->I = qe->NMPS;
    107         } else {
    108             A = qe->Qe;
    109             D = 1 - pCX->MPS;
    110             if(qe->nSwitch == 1) {
    111                 pCX->MPS = 1 - pCX->MPS;
    112             }
    113             pCX->I = qe->NLPS;
    114         }
    115         do {
    116             if (CT == 0) {
    117                 BYTEIN();
    118             }
    119             A <<= 1;
    120             C <<= 1;
    121             CT--;
    122         } while ((A & 0x8000) == 0);
    123     }
    124     return D;
    125 }
    126 #endif
    127