1 files changed, 66 insertions, 0 deletions
diff --git a/generator/src/main/java/com/google/archivepatcher/generator/similarity/Crc32SimilarityFinder.java b/generator/src/main/java/com/google/archivepatcher/generator/similarity/Crc32SimilarityFinder.java
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--- /dev/null
+++ b/generator/src/main/java/com/google/archivepatcher/generator/similarity/Crc32SimilarityFinder.java
@@ -0,0 +1,66 @@
+// Copyright 2016 Google Inc. All rights reserved.
+//
+// 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.
+
+package com.google.archivepatcher.generator.similarity;
+
+import com.google.archivepatcher.generator.MinimalZipEntry;
+
+import java.io.File;
+import java.util.Collection;
+import java.util.Collections;
+import java.util.HashMap;
+import java.util.LinkedList;
+import java.util.List;
+import java.util.Map;
+
+/**
+ * Detects identical files on the basis of the CRC32 of uncompressed content. All entries that have
+ * the same CRC32 will be identified as similar (and presumably are identical, in the absence of
+ * hash collisions).
+ */
+public class Crc32SimilarityFinder extends SimilarityFinder {
+
+  /**
+   * All entries in the base archive, organized by CRC32.
+   */
+  private final Map<Long, List<MinimalZipEntry>> baseEntriesByCrc32 = new HashMap<>();
+
+  /**
+   * Constructs a new similarity finder with the specified parameters.
+   * @param baseArchive the base archive that contains the entries to be searched
+   * @param baseEntries the entries in the base archive that are eligible to be searched
+   */
+  public Crc32SimilarityFinder(File baseArchive, Collection<MinimalZipEntry> baseEntries) {
+    super(baseArchive, baseEntries);
+    for (MinimalZipEntry oldEntry : baseEntries) {
+      long crc32 = oldEntry.getCrc32OfUncompressedData();
+      List<MinimalZipEntry> entriesForCrc32 = baseEntriesByCrc32.get(crc32);
+      if (entriesForCrc32 == null) {
+        entriesForCrc32 = new LinkedList<>();
+        baseEntriesByCrc32.put(crc32, entriesForCrc32);
+      }
+      entriesForCrc32.add(oldEntry);
+    }
+  }
+
+  @Override
+  public List<MinimalZipEntry> findSimilarFiles(File newArchive, MinimalZipEntry newEntry) {
+    List<MinimalZipEntry> matchedEntries =
+        baseEntriesByCrc32.get(newEntry.getCrc32OfUncompressedData());
+    if (matchedEntries == null) {
+      return Collections.emptyList();
+    }
+    return Collections.unmodifiableList(matchedEntries);
+  }
+}