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      1 /*
      2  * Copyright (C) 2016 The Android Open Source Project
      3  *
      4  * Licensed under the Apache License, Version 2.0 (the "License");
      5  * you may not use this file except in compliance with the License.
      6  * You may obtain a copy of the License at
      7  *
      8  *      http://www.apache.org/licenses/LICENSE-2.0
      9  *
     10  * Unless required by applicable law or agreed to in writing, software
     11  * distributed under the License is distributed on an "AS IS" BASIS,
     12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
     13  * See the License for the specific language governing permissions and
     14  * limitations under the License.
     15  */
     16 
     17 #ifndef ART_LIBDEXFILE_DEX_STRING_REFERENCE_H_
     18 #define ART_LIBDEXFILE_DEX_STRING_REFERENCE_H_
     19 
     20 #include <stdint.h>
     21 
     22 #include <android-base/logging.h>
     23 
     24 #include "dex/dex_file-inl.h"
     25 #include "dex/dex_file_reference.h"
     26 #include "dex/dex_file_types.h"
     27 #include "dex/utf-inl.h"
     28 
     29 namespace art {
     30 
     31 // A string is located by its DexFile and the string_ids_ table index into that DexFile.
     32 class StringReference : public DexFileReference {
     33  public:
     34   StringReference(const DexFile* file, dex::StringIndex index)
     35      : DexFileReference(file, index.index_) {}
     36 
     37   dex::StringIndex StringIndex() const {
     38     return dex::StringIndex(index);
     39   }
     40 
     41   const char* GetStringData() const {
     42     return dex_file->GetStringData(dex_file->GetStringId(StringIndex()));
     43   }
     44 };
     45 
     46 // Compare the actual referenced string values. Used for string reference deduplication.
     47 struct StringReferenceValueComparator {
     48   bool operator()(const StringReference& sr1, const StringReference& sr2) const {
     49     // Note that we want to deduplicate identical strings even if they are referenced
     50     // by different dex files, so we need some (any) total ordering of strings, rather
     51     // than references. However, the references should usually be from the same dex file,
     52     // so we choose the dex file string ordering so that we can simply compare indexes
     53     // and avoid the costly string comparison in the most common case.
     54     if (sr1.dex_file == sr2.dex_file) {
     55       // Use the string order enforced by the dex file verifier.
     56       DCHECK_EQ(
     57           sr1.index < sr2.index,
     58           CompareModifiedUtf8ToModifiedUtf8AsUtf16CodePointValues(sr1.GetStringData(),
     59                                                                   sr2.GetStringData()) < 0);
     60       return sr1.index < sr2.index;
     61     } else {
     62       // Cannot compare indexes, so do the string comparison.
     63       return CompareModifiedUtf8ToModifiedUtf8AsUtf16CodePointValues(sr1.GetStringData(),
     64                                                                      sr2.GetStringData()) < 0;
     65     }
     66   }
     67 };
     68 
     69 }  // namespace art
     70 
     71 #endif  // ART_LIBDEXFILE_DEX_STRING_REFERENCE_H_
     72