LUCENE-2771: add MultiNorms (forgot to svn add)

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/trunk@1055243 13f79535-47bb-0310-9956-ffa450edef68

lucene/src/java/org/apache/lucene/index/MultiNorms.java

@@ -0,0 +1,86 @@
+package org.apache.lucene.index;
+
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You 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.
+ */
+
+import java.io.IOException;
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.List;
+
+import org.apache.lucene.search.Similarity;
+import org.apache.lucene.util.ReaderUtil;
+
+/**
+ * Exposes flex API, merged from flex API of sub-segments.
+ * This is useful when you're interacting with an {@link
+ * IndexReader} implementation that consists of sequential
+ * sub-readers (eg DirectoryReader or {@link
+ * MultiReader}).
+ *
+ * <p><b>NOTE</b>: for multi readers, you'll get better
+ * performance by gathering the sub readers using {@link
+ * ReaderUtil#gatherSubReaders} and then operate per-reader,
+ * instead of using this class.
+ *
+ * @lucene.experimental
+ */
+public class MultiNorms {
+  /**
+   * Warning: this is heavy! Do not use in a loop, or implement norms()
+   * in your own reader with this (you should likely cache the result).
+   */
+  public static byte[] norms(IndexReader r, String field) throws IOException {
+    final IndexReader[] subs = r.getSequentialSubReaders();
+    if (subs == null) {
+      // already an atomic reader
+      return r.norms(field);
+    } else if (subs.length == 0 || !r.hasNorms(field)) {
+      // no norms
+      return null;
+    } else if (subs.length == 1) {
+      return norms(subs[0], field);
+    } else {
+      // TODO: optimize more maybe
+      byte norms[] = new byte[r.maxDoc()];
+      final List<IndexReader> leaves = new ArrayList<IndexReader>();
+      ReaderUtil.gatherSubReaders(leaves, r);
+      int end = 0;
+      for (IndexReader leaf : leaves) {
+        int start = end;
+        leaf.norms(field, norms, start);
+        end += leaf.maxDoc();
+      }
+      return norms;
+    }
+  }
+  
+  /**
+   * Warning: this is heavy! Do not use in a loop, or implement norms()
+   * in your own reader with this (you should likely cache the result).
+   */
+  public static void norms(IndexReader r, String field, byte[] bytes, int offset)
+      throws IOException {
+    // TODO: optimize more maybe
+    byte[] norms = norms(r, field);
+    if (norms == null) {
+      Arrays.fill(bytes, offset, bytes.length, Similarity.getDefault().encodeNormValue(1.0f));
+    } else {
+      System.arraycopy(norms, 0, bytes, offset, r.maxDoc());
+    }
+  }
+}