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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_RUNTIME_STRING_REFERENCE_H_
     18 #define ART_RUNTIME_STRING_REFERENCE_H_
     19 
     20 #include <stdint.h>
     21 
     22 #include "base/logging.h"
     23 #include "dex_file-inl.h"
     24 #include "dex_file_types.h"
     25 #include "utf-inl.h"
     26 
     27 namespace art {
     28 
     29 // A string is located by its DexFile and the string_ids_ table index into that DexFile.
     30 struct StringReference {
     31   StringReference(const DexFile* file, dex::StringIndex index)
     32       : dex_file(file), string_index(index) { }
     33 
     34   const char* GetStringData() const {
     35     return dex_file->GetStringData(dex_file->GetStringId(string_index));
     36   }
     37 
     38   const DexFile* dex_file;
     39   dex::StringIndex string_index;
     40 };
     41 
     42 // Compare only the reference and not the string contents.
     43 struct StringReferenceComparator {
     44   bool operator()(const StringReference& a, const StringReference& b) const {
     45     if (a.dex_file != b.dex_file) {
     46       return a.dex_file < b.dex_file;
     47     }
     48     return a.string_index < b.string_index;
     49   }
     50 };
     51 
     52 // Compare the actual referenced string values. Used for string reference deduplication.
     53 struct StringReferenceValueComparator {
     54   bool operator()(StringReference sr1, StringReference sr2) const {
     55     // Note that we want to deduplicate identical strings even if they are referenced
     56     // by different dex files, so we need some (any) total ordering of strings, rather
     57     // than references. However, the references should usually be from the same dex file,
     58     // so we choose the dex file string ordering so that we can simply compare indexes
     59     // and avoid the costly string comparison in the most common case.
     60     if (sr1.dex_file == sr2.dex_file) {
     61       // Use the string order enforced by the dex file verifier.
     62       DCHECK_EQ(
     63           sr1.string_index < sr2.string_index,
     64           CompareModifiedUtf8ToModifiedUtf8AsUtf16CodePointValues(sr1.GetStringData(),
     65                                                                   sr2.GetStringData()) < 0);
     66       return sr1.string_index < sr2.string_index;
     67     } else {
     68       // Cannot compare indexes, so do the string comparison.
     69       return CompareModifiedUtf8ToModifiedUtf8AsUtf16CodePointValues(sr1.GetStringData(),
     70                                                                      sr2.GetStringData()) < 0;
     71     }
     72   }
     73 };
     74 
     75 }  // namespace art
     76 
     77 #endif  // ART_RUNTIME_STRING_REFERENCE_H_
     78