From 28ccc0645c4a0d0c50128fadbaccec051b8e556e Mon Sep 17 00:00:00 2001
From: al <al@addthis.com>
Date: Fri, 9 Jun 2017 00:16:19 -0400
Subject: [PATCH 1/3] Add intersect method to bloom filter

---
 .../stream/membership/BloomFilter.java          | 17 +++++++++++++++++
 .../stream/membership/BloomFilterTest.java      | 12 ++++++++++++
 2 files changed, 29 insertions(+)

diff --git a/src/main/java/com/clearspring/analytics/stream/membership/BloomFilter.java b/src/main/java/com/clearspring/analytics/stream/membership/BloomFilter.java
index a374b088a..eeb8995ad 100644
--- a/src/main/java/com/clearspring/analytics/stream/membership/BloomFilter.java
+++ b/src/main/java/com/clearspring/analytics/stream/membership/BloomFilter.java
@@ -144,6 +144,23 @@ public Filter merge(Filter... filters) {
         return merged;
     }
 
+    /**
+     * Intersect a Bloom Filter with a number of other bloom filters.
+     * @param filters
+     * @return a new Bloom Filter that has each filter bit set if and only if all the input bloom filters had that bit set
+     */
+    public Filter intersect(Filter... filters) {
+        BitSet intersection = (BitSet) this.filter().clone();
+        BloomFilter intersectionBloomFilter = new BloomFilter(this.getHashCount(), intersection);
+        for (Filter otherFilter : filters) {
+            if (!(otherFilter instanceof BloomFilter || this.hashCount != otherFilter.hashCount)) {
+                throw new IllegalArgumentException(("Cannot merge filters of different class or size"));
+            }
+            intersection.and(((BloomFilter) otherFilter).filter());
+        }
+        return intersectionBloomFilter;
+    }
+
     /**
      * @return a BloomFilter that always returns a positive match, for testing
      */
diff --git a/src/test/java/com/clearspring/analytics/stream/membership/BloomFilterTest.java b/src/test/java/com/clearspring/analytics/stream/membership/BloomFilterTest.java
index 178d53c6a..04734c89f 100644
--- a/src/test/java/com/clearspring/analytics/stream/membership/BloomFilterTest.java
+++ b/src/test/java/com/clearspring/analytics/stream/membership/BloomFilterTest.java
@@ -76,6 +76,18 @@ public void testMerge() {
         assertTrue(mergeBf.isPresent("c"));
     }
 
+    @Test
+    public void testIntersect() {
+        bf.add("a");
+        bf.add("b");
+        bf2.add("a");
+        bf2.add("c");
+        BloomFilter intersectionBf = (BloomFilter) bf.intersect(bf2);
+        assertTrue(intersectionBf.isPresent("a"));
+        assertFalse(intersectionBf.isPresent("b"));
+        assertFalse(intersectionBf.isPresent("c"));
+    }
+
     @Test(expected=IllegalArgumentException.class)
     public void testMergeException() {
         BloomFilter bf3 = new BloomFilter(ELEMENTS*10, 1);

From 6e557c8f14ee4ab53a23c9c55db28c68467be381 Mon Sep 17 00:00:00 2001
From: al <al@addthis.com>
Date: Fri, 9 Jun 2017 00:26:11 -0400
Subject: [PATCH 2/3] Minor tweak - ensure unit test blooms are reset with each
 test

---
 .../clearspring/analytics/stream/membership/BloomFilterTest.java | 1 +
 1 file changed, 1 insertion(+)

diff --git a/src/test/java/com/clearspring/analytics/stream/membership/BloomFilterTest.java b/src/test/java/com/clearspring/analytics/stream/membership/BloomFilterTest.java
index 04734c89f..59a59a1b6 100644
--- a/src/test/java/com/clearspring/analytics/stream/membership/BloomFilterTest.java
+++ b/src/test/java/com/clearspring/analytics/stream/membership/BloomFilterTest.java
@@ -55,6 +55,7 @@ public BloomFilterTest() {
     @Before
     public void clear() {
         bf.clear();
+        bf2.clear();
     }
 
     @Test

From 3c4978311594ea3fc9ea016efb56f0c8c3915da0 Mon Sep 17 00:00:00 2001
From: al <al@addthis.com>
Date: Fri, 9 Jun 2017 00:29:04 -0400
Subject: [PATCH 3/3] Fix bloom filter compatibility check

---
 .../clearspring/analytics/stream/membership/BloomFilter.java    | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/main/java/com/clearspring/analytics/stream/membership/BloomFilter.java b/src/main/java/com/clearspring/analytics/stream/membership/BloomFilter.java
index eeb8995ad..9fc5561ab 100644
--- a/src/main/java/com/clearspring/analytics/stream/membership/BloomFilter.java
+++ b/src/main/java/com/clearspring/analytics/stream/membership/BloomFilter.java
@@ -153,7 +153,7 @@ public Filter intersect(Filter... filters) {
         BitSet intersection = (BitSet) this.filter().clone();
         BloomFilter intersectionBloomFilter = new BloomFilter(this.getHashCount(), intersection);
         for (Filter otherFilter : filters) {
-            if (!(otherFilter instanceof BloomFilter || this.hashCount != otherFilter.hashCount)) {
+            if (!(otherFilter instanceof BloomFilter) || this.hashCount != otherFilter.hashCount) {
                 throw new IllegalArgumentException(("Cannot merge filters of different class or size"));
             }
             intersection.and(((BloomFilter) otherFilter).filter());