Clean up CPDF_HintTables::LoadHintStream a little.

core/fpdfapi/fpdf_parser/cpdf_hint_tables.cpp

 // Copyright 2016 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/fpdfapi/fpdf_parser/cpdf_hint_tables.h"
 
 #include "core/fpdfapi/fpdf_parser/include/cpdf_data_avail.h"
 #include "core/fpdfapi/fpdf_parser/include/cpdf_array.h"
@@ skipping 410 matching lines @@
 FX_BOOL CPDF_HintTables::LoadHintStream(CPDF_Stream* pHintStream) {
   if (!pHintStream || !m_pLinearizedDict)
     return FALSE;
 
   CPDF_Dictionary* pDict = pHintStream->GetDict();
   CPDF_Object* pOffset = pDict ? pDict->GetObjectBy("S") : nullptr;
   if (!pOffset || !pOffset->IsNumber())
     return FALSE;
 
   int shared_hint_table_offset = pOffset->GetInteger();
+  if (shared_hint_table_offset <= 0)
+    return FALSE;
+
   CPDF_StreamAcc acc;
   acc.LoadAllData(pHintStream);
 
   uint32_t size = acc.GetSize();
   // The header section of page offset hint table is 36 bytes.
   // The header section of shared object hint table is 24 bytes.
   // Hint table has at least 60 bytes.
-  const uint32_t MIN_STREAM_LEN = 60;
-  if (size < MIN_STREAM_LEN || shared_hint_table_offset <= 0 ||
-      size < static_cast<uint32_t>(shared_hint_table_offset)) {
+  const uint32_t kMinStreamLength = 60;
+  if (size < kMinStreamLength)
+    return FALSE;
+
+  FX_SAFE_UINT32 safe_shared_hint_table_offset = shared_hint_table_offset;
+  if (!safe_shared_hint_table_offset.IsValid() ||
+      size < safe_shared_hint_table_offset.ValueOrDie()) {
     return FALSE;
   }
 
   CFX_BitStream bs;
   bs.Init(acc.GetData(), size);
   return ReadPageHintTable(&bs) &&
-         ReadSharedObjHintTable(&bs, pdfium::base::checked_cast<uint32_t>(
-                                         shared_hint_table_offset));
+         ReadSharedObjHintTable(&bs, shared_hint_table_offset);
 }
 
 int CPDF_HintTables::ReadPrimaryHintStreamOffset() const {
   if (!m_pLinearizedDict)
     return -1;
 
   CPDF_Array* pRange = m_pLinearizedDict->GetArrayBy("H");
   if (!pRange)
     return -1;
 
@@ skipping 11 matching lines @@
   CPDF_Array* pRange = m_pLinearizedDict->GetArrayBy("H");
   if (!pRange)
     return -1;
 
   CPDF_Object* pStreamLen = pRange->GetDirectObjectAt(1);
   if (!pStreamLen)
     return -1;
 
   return pStreamLen->GetInteger();
 }