Merge pull request #41 from FastFilter/dlemire/issue40

Fixing issue 40.
FastFilter · Oct 10, 2023 · 18dd1a7 · 18dd1a7
2 parents 7947763 + 746ea5b
commit 18dd1a7
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Showing 3 changed files with 9 additions and 4 deletions.
diff --git a/fastfilter/src/main/java/org/fastfilter/utils/Hash.java b/fastfilter/src/main/java/org/fastfilter/utils/Hash.java
@@ -32,7 +32,7 @@ public static long randomSeed() {
      */
     public static int reduce(int hash, int n) {
         // http://lemire.me/blog/2016/06/27/a-fast-alternative-to-the-modulo-reduction/
-        return (int) (((hash & 0xffffffffL) * n) >>> 32);
+        return (int) (((hash & 0xffffffffL) * (n & 0xffffffffL)) >>> 32);
     }
 
     /**

diff --git a/fastfilter/src/test/java/org/fastfilter/RegressionTests.java b/fastfilter/src/test/java/org/fastfilter/RegressionTests.java
@@ -79,4 +79,12 @@ public void regressionTest() {
             assertTrue(filter.mayContain(key));
         }
     }
+
+    @Test
+    public void issue40() {
+        long hash = 4282432426L;
+        long n = 2400000016L; // important: exceeds 2147483647
+        long r = (long)(Hash.reduce((int)hash, (int)n) & 0xffffffffL);
+        assertTrue(r < n);
+    }
 }
diff --git a/fastfilter/src/test/java/org/fastfilter/TestAllFilters.java b/fastfilter/src/test/java/org/fastfilter/TestAllFilters.java
@@ -183,9 +183,6 @@ private static void test(TestFilterType type, int len, int seed, boolean log) {
             }
             time = System.nanoTime() - time;
             nanosPerRemove = time / len;
-if (f.cardinality() != 0) {
-    System.out.println(f.cardinality());
-}
             assertEquals(f.toString(), 0, f.cardinality());
         }
         if (log) {