[commons-math] 03/03: Fix overflow bug in stirlingS2 when n > 64, k = 2

[aherbert]

This is an automated email from the ASF dual-hosted git repository.

aherbert pushed a commit to branch master
in repository https://gitbox.apache.org/repos/asf/commons-math.git

commit fc239a64be75066a1ab07bfae273ffcc5902fa7e
Author: aherbert <aherb...@apache.org>
AuthorDate: Mon Oct 31 11:08:52 2022 +0000

    Fix overflow bug in stirlingS2 when n > 64, k = 2
---
 .../java/org/apache/commons/math4/legacy/util/CombinatoricsUtils.java | 4 ++++
 .../org/apache/commons/math4/legacy/util/CombinatoricsUtilsTest.java  | 3 +++
 2 files changed, 7 insertions(+)

diff --git 
a/commons-math-legacy/src/main/java/org/apache/commons/math4/legacy/util/CombinatoricsUtils.java
 
b/commons-math-legacy/src/main/java/org/apache/commons/math4/legacy/util/CombinatoricsUtils.java
index 7e07fa034..e4e9c679b 100644
--- 
a/commons-math-legacy/src/main/java/org/apache/commons/math4/legacy/util/CombinatoricsUtils.java
+++ 
b/commons-math-legacy/src/main/java/org/apache/commons/math4/legacy/util/CombinatoricsUtils.java
@@ -101,6 +101,10 @@ public final class CombinatoricsUtils {
             } else if (k == 1 || k == n) {
                 return 1;
             } else if (k == 2) {
+                if (n > 64) {
+                    throw new 
MathArithmeticException(LocalizedFormats.ARGUMENT_OUTSIDE_DOMAIN,
+                        n, 0, stirlingS2.length - 1);
+                }
                 return (1L << (n - 1)) - 1L;
             } else if (k == n - 1) {
                 return BinomialCoefficient.value(n, 2);
diff --git 
a/commons-math-legacy/src/test/java/org/apache/commons/math4/legacy/util/CombinatoricsUtilsTest.java
 
b/commons-math-legacy/src/test/java/org/apache/commons/math4/legacy/util/CombinatoricsUtilsTest.java
index e1fbe8880..19e5d8a59 100644
--- 
a/commons-math-legacy/src/test/java/org/apache/commons/math4/legacy/util/CombinatoricsUtilsTest.java
+++ 
b/commons-math-legacy/src/test/java/org/apache/commons/math4/legacy/util/CombinatoricsUtilsTest.java
@@ -82,5 +82,8 @@ public class CombinatoricsUtilsTest {
     @Test
     public void testStirlingS2Overflow() {
         Assertions.assertThrows(MathArithmeticException.class, () -> 
CombinatoricsUtils.stirlingS2(26, 9));
+
+        Assertions.assertEquals(9223372036854775807L, 
CombinatoricsUtils.stirlingS2(64, 2));
+        Assertions.assertThrows(MathArithmeticException.class, () -> 
CombinatoricsUtils.stirlingS2(65, 2));
     }
 }