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 "core/fxcodec/jbig2/JBig2_ArithDecoder.h"
8
9 #include "core/fxcodec/jbig2/JBig2_BitStream.h"
10 #include "core/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}, {0x3401, 2, 6, 0}, {0x1801, 3, 9, 0},
24 {0x0AC1, 4, 12, 0}, {0x0521, 5, 29, 0}, {0x0221, 38, 33, 0},
25 {0x5601, 7, 6, 1}, {0x5401, 8, 14, 0}, {0x4801, 9, 14, 0},
26 {0x3801, 10, 14, 0}, {0x3001, 11, 17, 0}, {0x2401, 12, 18, 0},
27 {0x1C01, 13, 20, 0}, {0x1601, 29, 21, 0}, {0x5601, 15, 14, 1},
28 {0x5401, 16, 14, 0}, {0x5101, 17, 15, 0}, {0x4801, 18, 16, 0},
29 {0x3801, 19, 17, 0}, {0x3401, 20, 18, 0}, {0x3001, 21, 19, 0},
30 {0x2801, 22, 19, 0}, {0x2401, 23, 20, 0}, {0x2201, 24, 21, 0},
31 {0x1C01, 25, 22, 0}, {0x1801, 26, 23, 0}, {0x1601, 27, 24, 0},
32 {0x1401, 28, 25, 0}, {0x1201, 29, 26, 0}, {0x1101, 30, 27, 0},
33 {0x0AC1, 31, 28, 0}, {0x09C1, 32, 29, 0}, {0x08A1, 33, 30, 0},
34 {0x0521, 34, 31, 0}, {0x0441, 35, 32, 0}, {0x02A1, 36, 33, 0},
35 {0x0221, 37, 34, 0}, {0x0141, 38, 35, 0}, {0x0111, 39, 36, 0},
36 {0x0085, 40, 37, 0}, {0x0049, 41, 38, 0}, {0x0025, 42, 39, 0},
37 {0x0015, 43, 40, 0}, {0x0009, 44, 41, 0}, {0x0005, 45, 42, 0},
38 {0x0001, 45, 43, 0}, {0x5601, 46, 46, 0}};
39
40 const unsigned int kDefaultAValue = 0x8000;
41
DecodeNMPS(JBig2ArithCtx * pCX,const JBig2ArithQe & qe)42 int DecodeNMPS(JBig2ArithCtx* pCX, const JBig2ArithQe& qe) {
43 pCX->I = qe.NMPS;
44 return pCX->MPS;
45 }
46
DecodeNLPS(JBig2ArithCtx * pCX,const JBig2ArithQe & qe)47 int DecodeNLPS(JBig2ArithCtx* pCX, const JBig2ArithQe& qe) {
48 // TODO(thestig): |D|, |MPS| and friends probably should be booleans.
49 int D = 1 - pCX->MPS;
50 if (qe.nSwitch == 1)
51 pCX->MPS = 1 - pCX->MPS;
52 pCX->I = qe.NLPS;
53 return D;
54 }
55
56 } // namespace
57
CJBig2_ArithDecoder(CJBig2_BitStream * pStream)58 CJBig2_ArithDecoder::CJBig2_ArithDecoder(CJBig2_BitStream* pStream)
59 : m_pStream(pStream) {
60 m_B = m_pStream->getCurByte_arith();
61 m_C = (m_B ^ 0xff) << 16;
62 BYTEIN();
63 m_C = m_C << 7;
64 m_CT = m_CT - 7;
65 m_A = kDefaultAValue;
66 }
67
~CJBig2_ArithDecoder()68 CJBig2_ArithDecoder::~CJBig2_ArithDecoder() {}
69
DECODE(JBig2ArithCtx * pCX)70 int CJBig2_ArithDecoder::DECODE(JBig2ArithCtx* pCX) {
71 if (!pCX || pCX->I >= FX_ArraySize(kQeTable))
72 return 0;
73
74 const JBig2ArithQe& qe = kQeTable[pCX->I];
75 m_A -= qe.Qe;
76 if ((m_C >> 16) < m_A) {
77 if (m_A & kDefaultAValue)
78 return pCX->MPS;
79
80 const int D = m_A < qe.Qe ? DecodeNLPS(pCX, qe) : DecodeNMPS(pCX, qe);
81 ReadValueA();
82 return D;
83 }
84
85 m_C -= m_A << 16;
86 const int D = m_A < qe.Qe ? DecodeNMPS(pCX, qe) : DecodeNLPS(pCX, qe);
87 m_A = qe.Qe;
88 ReadValueA();
89 return D;
90 }
91
BYTEIN()92 void CJBig2_ArithDecoder::BYTEIN() {
93 unsigned char B1;
94 if (m_B == 0xff) {
95 B1 = m_pStream->getNextByte_arith();
96 if (B1 > 0x8f) {
97 m_CT = 8;
98 } else {
99 m_pStream->incByteIdx();
100 m_B = B1;
101 m_C = m_C + 0xfe00 - (m_B << 9);
102 m_CT = 7;
103 }
104 } else {
105 m_pStream->incByteIdx();
106 m_B = m_pStream->getCurByte_arith();
107 m_C = m_C + 0xff00 - (m_B << 8);
108 m_CT = 8;
109 }
110 }
111
ReadValueA()112 void CJBig2_ArithDecoder::ReadValueA() {
113 do {
114 if (m_CT == 0)
115 BYTEIN();
116 m_A <<= 1;
117 m_C <<= 1;
118 --m_CT;
119 } while ((m_A & kDefaultAValue) == 0);
120 }
121