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// Copyright 2014 PDFium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
// Original code copyright 2014 Foxit Software Inc. http://www.foxitsoftware.com
#include "core/fxcodec/jbig2/JBig2_ArithIntDecoder.h"
#include <vector>
#include "core/fxcrt/fx_memory.h"
namespace {
int ShiftOr(int val, int bitwise_or_val) {
return (val << 1) | bitwise_or_val;
}
const struct ArithIntDecodeData {
int nNeedBits;
int nValue;
} g_ArithIntDecodeData[] = {
{2, 0}, {4, 4}, {6, 20}, {8, 84}, {12, 340}, {32, 4436},
};
size_t RecursiveDecode(CJBig2_ArithDecoder* decoder,
std::vector<JBig2ArithCtx>* context,
int* prev,
size_t depth) {
static const size_t kDepthEnd = FX_ArraySize(g_ArithIntDecodeData) - 1;
if (depth == kDepthEnd)
return kDepthEnd;
JBig2ArithCtx* pCX = &(*context)[*prev];
int D = decoder->Decode(pCX);
*prev = ShiftOr(*prev, D);
if (!D)
return depth;
return RecursiveDecode(decoder, context, prev, depth + 1);
}
} // namespace
CJBig2_ArithIntDecoder::CJBig2_ArithIntDecoder() {
m_IAx.resize(512);
}
CJBig2_ArithIntDecoder::~CJBig2_ArithIntDecoder() {}
bool CJBig2_ArithIntDecoder::Decode(CJBig2_ArithDecoder* pArithDecoder,
int* nResult) {
// This decoding algorithm is explained in "Annex A - Arithmetic Integer
// Decoding Procedure" on page 113 of the JBIG2 specification (ISO/IEC FCD
// 14492).
int PREV = 1;
const int S = pArithDecoder->Decode(&m_IAx[PREV]);
PREV = ShiftOr(PREV, S);
const size_t nDecodeDataIndex =
RecursiveDecode(pArithDecoder, &m_IAx, &PREV, 0);
int nTemp = 0;
for (int i = 0; i < g_ArithIntDecodeData[nDecodeDataIndex].nNeedBits; ++i) {
int D = pArithDecoder->Decode(&m_IAx[PREV]);
PREV = ShiftOr(PREV, D);
if (PREV >= 256)
PREV = (PREV & 511) | 256;
nTemp = ShiftOr(nTemp, D);
}
pdfium::base::CheckedNumeric<int> safeValue =
g_ArithIntDecodeData[nDecodeDataIndex].nValue;
safeValue += nTemp;
// Value does not fit in int.
if (!safeValue.IsValid()) {
*nResult = 0;
return false;
}
int nValue = safeValue.ValueOrDie();
if (S == 1 && nValue > 0)
nValue = -nValue;
*nResult = nValue;
return S != 1 || nValue != 0;
}
CJBig2_ArithIaidDecoder::CJBig2_ArithIaidDecoder(unsigned char SBSYMCODELENA)
: SBSYMCODELEN(SBSYMCODELENA) {
m_IAID.resize(static_cast<size_t>(1) << SBSYMCODELEN);
}
CJBig2_ArithIaidDecoder::~CJBig2_ArithIaidDecoder() {}
void CJBig2_ArithIaidDecoder::Decode(CJBig2_ArithDecoder* pArithDecoder,
uint32_t* nResult) {
int PREV = 1;
for (unsigned char i = 0; i < SBSYMCODELEN; ++i) {
JBig2ArithCtx* pCX = &m_IAID[PREV];
int D = pArithDecoder->Decode(pCX);
PREV = ShiftOr(PREV, D);
}
*nResult = PREV - (1 << SBSYMCODELEN);
}
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