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 };
CJBig2_ArithDecoder(CJBig2_BitStream * pStream)36 inline CJBig2_ArithDecoder::CJBig2_ArithDecoder(CJBig2_BitStream *pStream)
37 {
38     m_pStream = pStream;
39     INITDEC();
40 }
~CJBig2_ArithDecoder()41 inline CJBig2_ArithDecoder::~CJBig2_ArithDecoder()
42 {
43 }
INITDEC()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 }
BYTEIN()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 }
DECODE(JBig2ArithCtx * pCX)73 inline int CJBig2_ArithDecoder::DECODE(JBig2ArithCtx *pCX)
74 {
75     if (!pCX || pCX->I >= JBIG2_QE_NUM) {
76         return 0;
77     }
78 
79     int D;
80     const JBig2ArithQe * qe = &QeTable[pCX->I];
81     A = A - qe->Qe;
82     if((C >> 16) < A) {
83         if(A & 0x8000) {
84             D = pCX->MPS;
85         } else {
86             if(A < qe->Qe) {
87                 D = 1 - pCX->MPS;
88                 if(qe->nSwitch == 1) {
89                     pCX->MPS = 1 - pCX->MPS;
90                 }
91                 pCX->I = qe->NLPS;
92             } else {
93                 D = pCX->MPS;
94                 pCX->I = qe->NMPS;
95             }
96             do {
97                 if (CT == 0) {
98                     BYTEIN();
99                 }
100                 A <<= 1;
101                 C <<= 1;
102                 CT--;
103             } while ((A & 0x8000) == 0);
104         }
105     } else {
106         C -= A << 16;
107         if(A < qe->Qe) {
108             A = qe->Qe;
109             D = pCX->MPS;
110             pCX->I = qe->NMPS;
111         } else {
112             A = qe->Qe;
113             D = 1 - pCX->MPS;
114             if(qe->nSwitch == 1) {
115                 pCX->MPS = 1 - pCX->MPS;
116             }
117             pCX->I = qe->NLPS;
118         }
119         do {
120             if (CT == 0) {
121                 BYTEIN();
122             }
123             A <<= 1;
124             C <<= 1;
125             CT--;
126         } while ((A & 0x8000) == 0);
127     }
128     return D;
129 }
130 #endif
131