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 {
StringReferenceStringReference31   StringReference(const DexFile* file, dex::StringIndex index)
32       : dex_file(file), string_index(index) { }
33 
GetStringDataStringReference34   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 {
operatorStringReferenceComparator44   bool operator()(const StringReference& a, const StringReference& b) {
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 {
operatorStringReferenceValueComparator54   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