From 7574f33abe6da0045dc1b6b23aa6d09c83f539e9 Mon Sep 17 00:00:00 2001
From: Uwe Schindler <uschindler@apache.org>
Date: Fri, 24 Jun 2011 20:43:46 +0000
Subject: [PATCH] LUCENE-3179: Fix bug in handling of indexes >= size in
 OpenBitSet.prevSetBit()

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/trunk@1139431 13f79535-47bb-0310-9956-ffa450edef68
---
 .../java/org/apache/lucene/util/OpenBitSet.java  | 16 ++++++++++------
 .../org/apache/lucene/util/TestOpenBitSet.java   |  4 ++--
 2 files changed, 12 insertions(+), 8 deletions(-)

diff --git a/lucene/src/java/org/apache/lucene/util/OpenBitSet.java b/lucene/src/java/org/apache/lucene/util/OpenBitSet.java
index 89a40dc1bf4..281faaa317c 100644
--- a/lucene/src/java/org/apache/lucene/util/OpenBitSet.java
+++ b/lucene/src/java/org/apache/lucene/util/OpenBitSet.java
@@ -664,15 +664,19 @@ public class OpenBitSet extends DocIdSet implements Bits, Cloneable {
    *  -1 is returned if there are no more set bits.
    */
   public int prevSetBit(int index) {
-    if (index < 0) {
-      return -1;
-    }
-    int i = index>>6;
+    int i = index >> 6;
+    final int subIndex;
+    long word;
     if (i >= wlen) {
       i = wlen - 1;
+      if (i < 0) return -1;
+      subIndex = 63;  // last possible bit
+      word = bits[i];
+    } else {
+      if (i < 0) return -1;
+      subIndex = index & 0x3f;  // index within the word
+      word = (bits[i] << (63-subIndex));  // skip all the bits to the left of index
     }
-    final int subIndex = index & 0x3f;      // index within the word
-    long word = (bits[i] << (63-subIndex));  // skip all the bits to the left of index
 
     if (word != 0) {
       return (i << 6) + subIndex - Long.numberOfLeadingZeros(word); // See LUCENE-3197
diff --git a/lucene/src/test/org/apache/lucene/util/TestOpenBitSet.java b/lucene/src/test/org/apache/lucene/util/TestOpenBitSet.java
index 34f6ba9eecf..61322fe67c2 100644
--- a/lucene/src/test/org/apache/lucene/util/TestOpenBitSet.java
+++ b/lucene/src/test/org/apache/lucene/util/TestOpenBitSet.java
@@ -42,8 +42,8 @@ public class TestOpenBitSet extends LuceneTestCase {
   }
 
   void doPrevSetBit(BitSet a, OpenBitSet b) {
-    int aa=a.length();
-    int bb=aa;
+    int aa = a.size() + random.nextInt(100);
+    int bb = aa;
     do {
       // aa = a.prevSetBit(aa-1);
       aa--;