1 // Copyright 2014 The PDFium Authors
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_ArithIntDecoder.h"
8
9 #include <vector>
10
11 #include "core/fxcrt/fx_safe_types.h"
12
13 namespace {
14
ShiftOr(int val,int bitwise_or_val)15 int ShiftOr(int val, int bitwise_or_val) {
16 return (val << 1) | bitwise_or_val;
17 }
18
19 struct ArithIntDecodeData {
20 int nNeedBits;
21 int nValue;
22 };
23
24 constexpr ArithIntDecodeData kArithIntDecodeData[] = {
25 {2, 0}, {4, 4}, {6, 20}, {8, 84}, {12, 340}, {32, 4436},
26 };
27
RecursiveDecode(CJBig2_ArithDecoder * decoder,std::vector<JBig2ArithCtx> * context,int * prev,size_t depth)28 size_t RecursiveDecode(CJBig2_ArithDecoder* decoder,
29 std::vector<JBig2ArithCtx>* context,
30 int* prev,
31 size_t depth) {
32 static const size_t kDepthEnd = std::size(kArithIntDecodeData) - 1;
33 if (depth == kDepthEnd)
34 return kDepthEnd;
35
36 JBig2ArithCtx* pCX = &(*context)[*prev];
37 int D = decoder->Decode(pCX);
38 *prev = ShiftOr(*prev, D);
39 if (!D)
40 return depth;
41 return RecursiveDecode(decoder, context, prev, depth + 1);
42 }
43
44 } // namespace
45
CJBig2_ArithIntDecoder()46 CJBig2_ArithIntDecoder::CJBig2_ArithIntDecoder() {
47 m_IAx.resize(512);
48 }
49
50 CJBig2_ArithIntDecoder::~CJBig2_ArithIntDecoder() = default;
51
Decode(CJBig2_ArithDecoder * pArithDecoder,int * nResult)52 bool CJBig2_ArithIntDecoder::Decode(CJBig2_ArithDecoder* pArithDecoder,
53 int* nResult) {
54 // This decoding algorithm is explained in "Annex A - Arithmetic Integer
55 // Decoding Procedure" on page 113 of the JBIG2 specification (ISO/IEC FCD
56 // 14492).
57 int PREV = 1;
58 const int S = pArithDecoder->Decode(&m_IAx[PREV]);
59 PREV = ShiftOr(PREV, S);
60
61 const size_t nDecodeDataIndex =
62 RecursiveDecode(pArithDecoder, &m_IAx, &PREV, 0);
63
64 int nTemp = 0;
65 for (int i = 0; i < kArithIntDecodeData[nDecodeDataIndex].nNeedBits; ++i) {
66 int D = pArithDecoder->Decode(&m_IAx[PREV]);
67 PREV = ShiftOr(PREV, D);
68 if (PREV >= 256)
69 PREV = (PREV & 511) | 256;
70 nTemp = ShiftOr(nTemp, D);
71 }
72 FX_SAFE_INT32 safeValue = kArithIntDecodeData[nDecodeDataIndex].nValue;
73 safeValue += nTemp;
74
75 // Value does not fit in int.
76 if (!safeValue.IsValid()) {
77 *nResult = 0;
78 return false;
79 }
80
81 int nValue = safeValue.ValueOrDie();
82 if (S == 1 && nValue > 0)
83 nValue = -nValue;
84
85 *nResult = nValue;
86 return S != 1 || nValue != 0;
87 }
88
CJBig2_ArithIaidDecoder(unsigned char SBSYMCODELENA)89 CJBig2_ArithIaidDecoder::CJBig2_ArithIaidDecoder(unsigned char SBSYMCODELENA)
90 : SBSYMCODELEN(SBSYMCODELENA) {
91 m_IAID.resize(static_cast<size_t>(1) << SBSYMCODELEN);
92 }
93
94 CJBig2_ArithIaidDecoder::~CJBig2_ArithIaidDecoder() = default;
95
Decode(CJBig2_ArithDecoder * pArithDecoder,uint32_t * nResult)96 void CJBig2_ArithIaidDecoder::Decode(CJBig2_ArithDecoder* pArithDecoder,
97 uint32_t* nResult) {
98 int PREV = 1;
99 for (unsigned char i = 0; i < SBSYMCODELEN; ++i) {
100 JBig2ArithCtx* pCX = &m_IAID[PREV];
101 int D = pArithDecoder->Decode(pCX);
102 PREV = ShiftOr(PREV, D);
103 }
104 *nResult = PREV - (1 << SBSYMCODELEN);
105 }
106