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 #include "JBig2_ArithDecoder.h"
8
9 #include "JBig2_BitStream.h"
10 #include "core/include/fxcrt/fx_basic.h"
11
12 namespace {
13
14 struct JBig2ArithQe {
15 unsigned int Qe;
16 unsigned int NMPS;
17 unsigned int NLPS;
18 unsigned int nSwitch;
19 };
20
21 const JBig2ArithQe kQeTable[] = {
22 // Stupid hack to keep clang-format from reformatting this badly.
23 {0x5601, 1, 1, 1},
24 {0x3401, 2, 6, 0},
25 {0x1801, 3, 9, 0},
26 {0x0AC1, 4, 12, 0},
27 {0x0521, 5, 29, 0},
28 {0x0221, 38, 33, 0},
29 {0x5601, 7, 6, 1},
30 {0x5401, 8, 14, 0},
31 {0x4801, 9, 14, 0},
32 {0x3801, 10, 14, 0},
33 {0x3001, 11, 17, 0},
34 {0x2401, 12, 18, 0},
35 {0x1C01, 13, 20, 0},
36 {0x1601, 29, 21, 0},
37 {0x5601, 15, 14, 1},
38 {0x5401, 16, 14, 0},
39 {0x5101, 17, 15, 0},
40 {0x4801, 18, 16, 0},
41 {0x3801, 19, 17, 0},
42 {0x3401, 20, 18, 0},
43 {0x3001, 21, 19, 0},
44 {0x2801, 22, 19, 0},
45 {0x2401, 23, 20, 0},
46 {0x2201, 24, 21, 0},
47 {0x1C01, 25, 22, 0},
48 {0x1801, 26, 23, 0},
49 {0x1601, 27, 24, 0},
50 {0x1401, 28, 25, 0},
51 {0x1201, 29, 26, 0},
52 {0x1101, 30, 27, 0},
53 {0x0AC1, 31, 28, 0},
54 {0x09C1, 32, 29, 0},
55 {0x08A1, 33, 30, 0},
56 {0x0521, 34, 31, 0},
57 {0x0441, 35, 32, 0},
58 {0x02A1, 36, 33, 0},
59 {0x0221, 37, 34, 0},
60 {0x0141, 38, 35, 0},
61 {0x0111, 39, 36, 0},
62 {0x0085, 40, 37, 0},
63 {0x0049, 41, 38, 0},
64 {0x0025, 42, 39, 0},
65 {0x0015, 43, 40, 0},
66 {0x0009, 44, 41, 0},
67 {0x0005, 45, 42, 0},
68 {0x0001, 45, 43, 0},
69 {0x5601, 46, 46, 0}};
70
71 const unsigned int kDefaultAValue = 0x8000;
72
DecodeNMPS(JBig2ArithCtx * pCX,const JBig2ArithQe & qe)73 int DecodeNMPS(JBig2ArithCtx* pCX, const JBig2ArithQe& qe) {
74 pCX->I = qe.NMPS;
75 return pCX->MPS;
76 }
77
DecodeNLPS(JBig2ArithCtx * pCX,const JBig2ArithQe & qe)78 int DecodeNLPS(JBig2ArithCtx* pCX, const JBig2ArithQe& qe) {
79 // TODO(thestig): |D|, |MPS| and friends probably should be booleans.
80 int D = 1 - pCX->MPS;
81 if (qe.nSwitch == 1)
82 pCX->MPS = 1 - pCX->MPS;
83 pCX->I = qe.NLPS;
84 return D;
85 }
86
87 } // namespace
88
CJBig2_ArithDecoder(CJBig2_BitStream * pStream)89 CJBig2_ArithDecoder::CJBig2_ArithDecoder(CJBig2_BitStream* pStream)
90 : m_pStream(pStream) {
91 m_B = m_pStream->getCurByte_arith();
92 m_C = (m_B ^ 0xff) << 16;
93 BYTEIN();
94 m_C = m_C << 7;
95 m_CT = m_CT - 7;
96 m_A = kDefaultAValue;
97 }
98
~CJBig2_ArithDecoder()99 CJBig2_ArithDecoder::~CJBig2_ArithDecoder() {
100 }
101
DECODE(JBig2ArithCtx * pCX)102 int CJBig2_ArithDecoder::DECODE(JBig2ArithCtx* pCX) {
103 if (!pCX || pCX->I >= FX_ArraySize(kQeTable))
104 return 0;
105
106 const JBig2ArithQe& qe = kQeTable[pCX->I];
107 m_A -= qe.Qe;
108 if ((m_C >> 16) < m_A) {
109 if (m_A & kDefaultAValue)
110 return pCX->MPS;
111
112 const int D = m_A < qe.Qe ? DecodeNLPS(pCX, qe) : DecodeNMPS(pCX, qe);
113 ReadValueA();
114 return D;
115 }
116
117 m_C -= m_A << 16;
118 const int D = m_A < qe.Qe ? DecodeNMPS(pCX, qe) : DecodeNLPS(pCX, qe);
119 m_A = qe.Qe;
120 ReadValueA();
121 return D;
122 }
123
BYTEIN()124 void CJBig2_ArithDecoder::BYTEIN() {
125 unsigned char B1;
126 if (m_B == 0xff) {
127 B1 = m_pStream->getNextByte_arith();
128 if (B1 > 0x8f) {
129 m_CT = 8;
130 } else {
131 m_pStream->incByteIdx();
132 m_B = B1;
133 m_C = m_C + 0xfe00 - (m_B << 9);
134 m_CT = 7;
135 }
136 } else {
137 m_pStream->incByteIdx();
138 m_B = m_pStream->getCurByte_arith();
139 m_C = m_C + 0xff00 - (m_B << 8);
140 m_CT = 8;
141 }
142 }
143
ReadValueA()144 void CJBig2_ArithDecoder::ReadValueA() {
145 do {
146 if (m_CT == 0)
147 BYTEIN();
148 m_A <<= 1;
149 m_C <<= 1;
150 --m_CT;
151 } while ((m_A & kDefaultAValue) == 0);
152 }
153