diff --git a/runtime/string_reference.h b/runtime/string_reference.h
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+/*
+ * Copyright (C) 2016 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef ART_RUNTIME_STRING_REFERENCE_H_
+#define ART_RUNTIME_STRING_REFERENCE_H_
+
+#include <stdint.h>
+
+#include "base/logging.h"
+#include "dex_file-inl.h"
+#include "utf-inl.h"
+
+namespace art {
+
+// A string is located by its DexFile and the string_ids_ table index into that DexFile.
+struct StringReference {
+  StringReference(const DexFile* file, uint32_t index) : dex_file(file), string_index(index) { }
+
+  const char* GetStringData() const {
+    return dex_file->GetStringData(dex_file->GetStringId(string_index));
+  }
+
+  const DexFile* dex_file;
+  uint32_t string_index;
+};
+
+// Compare only the reference and not the string contents.
+struct StringReferenceComparator {
+  bool operator()(const StringReference& a, const StringReference& b) {
+    if (a.dex_file != b.dex_file) {
+      return a.dex_file < b.dex_file;
+    }
+    return a.string_index < b.string_index;
+  }
+};
+
+// Compare the actual referenced string values. Used for string reference deduplication.
+struct StringReferenceValueComparator {
+  bool operator()(StringReference sr1, StringReference sr2) const {
+    // Note that we want to deduplicate identical strings even if they are referenced
+    // by different dex files, so we need some (any) total ordering of strings, rather
+    // than references. However, the references should usually be from the same dex file,
+    // so we choose the dex file string ordering so that we can simply compare indexes
+    // and avoid the costly string comparison in the most common case.
+    if (sr1.dex_file == sr2.dex_file) {
+      // Use the string order enforced by the dex file verifier.
+      DCHECK_EQ(
+          sr1.string_index < sr2.string_index,
+          CompareModifiedUtf8ToModifiedUtf8AsUtf16CodePointValues(sr1.GetStringData(),
+                                                                  sr2.GetStringData()) < 0);
+      return sr1.string_index < sr2.string_index;
+    } else {
+      // Cannot compare indexes, so do the string comparison.
+      return CompareModifiedUtf8ToModifiedUtf8AsUtf16CodePointValues(sr1.GetStringData(),
+                                                                     sr2.GetStringData()) < 0;
+    }
+  }
+};
+
+}  // namespace art
+
+#endif  // ART_RUNTIME_STRING_REFERENCE_H_