Index: lucene/src/java/org/apache/lucene/util/ArrayUtil.java
===================================================================
--- lucene/src/java/org/apache/lucene/util/ArrayUtil.java	(revision 1097776)
+++ lucene/src/java/org/apache/lucene/util/ArrayUtil.java	(working copy)
@@ -17,8 +17,12 @@
  * limitations under the License.
  */
 
+import java.lang.reflect.Array;
+import java.util.Arrays;
 import java.util.Collection;
+import java.util.Collections;
 import java.util.Comparator;
+import java.util.List;
 
 /**
  * Methods for manipulating arrays.
@@ -584,6 +588,7 @@
   public static <T extends Comparable<? super T>> void quickSort(T[] a, int fromIndex, int toIndex) {
     if (toIndex-fromIndex <= 1) return;
     getSorter(a).quickSort(fromIndex, toIndex-1);
+    assert saneComparator(a, fromIndex, toIndex);
   }
   
   /**
@@ -594,6 +599,33 @@
     quickSort(a, 0, a.length);
   }
 
+  private static <T extends Comparable<? super T>> boolean saneComparator(T[] a, int fromIndex, int toIndex) {
+    T[] a2 = copyOfRange(a, fromIndex, toIndex);
+    List<T> a2l = Arrays.asList(a2);
+    Collections.reverse(a2l);
+    a2 = a2l.toArray(a2);
+    Arrays.sort(a2, 0, a2.length);
+    for (int i = 0; i < a2.length; i++) {
+      assert a2[i].equals(a[fromIndex+i]) : "insane comparator for: " + a.getClass().getComponentType().getName();
+    }
+    return true;
+  }
+  
+  // apache harmony copyfRange
+  @SuppressWarnings("unchecked")
+  public static <T> T[] copyOfRange(T[] original, int start, int end) {
+    if (original.length >= start && 0 <= start) {
+      if (start <= end) {
+        int length = end - start;
+        int copyLength = Math.min(length, original.length - start);
+        T[] copy = (T[]) Array.newInstance(original.getClass().getComponentType(), length);
+        System.arraycopy(original, start, copy, 0, copyLength);
+        return copy;
+      }
+      throw new IllegalArgumentException();
+    }
+    throw new ArrayIndexOutOfBoundsException();
+  }
   // mergeSorts:
   
   /**