From 89b6abf93bcccf0a04c480b98b840fa07a4d00fd Mon Sep 17 00:00:00 2001
From: PHJ2000 <105151063+PHJ2000@users.noreply.github.com>
Date: Mon, 5 Oct 2026 00:35:14 +0900
Subject: [PATCH] Fix long overflow in CosineSimilarity dot product

Accumulate products in double so identical vectors with large integer
components retain a cosine similarity of one. Individual products still
use long arithmetic before being added to the accumulator.

Add regression coverage for identical vectors with ordinary, maximum,
and minimum integer components. The two large-component cases fail
without the accumulator change.

Generated-by: OpenAI Codex
---
 .../commons/text/similarity/CosineSimilarity.java    |  2 +-
 .../text/similarity/CosineSimilarityTest.java        | 12 ++++++++++++
 2 files changed, 13 insertions(+), 1 deletion(-)

diff --git a/src/main/java/org/apache/commons/text/similarity/CosineSimilarity.java b/src/main/java/org/apache/commons/text/similarity/CosineSimilarity.java
index 2c5a123b72..73fff3077b 100644
--- a/src/main/java/org/apache/commons/text/similarity/CosineSimilarity.java
+++ b/src/main/java/org/apache/commons/text/similarity/CosineSimilarity.java
@@ -86,7 +86,7 @@ public Double cosineSimilarity(final Map<CharSequence, Integer> leftVector, fina
      * @return The dot product.
      */
     private double dot(final Map<CharSequence, Integer> leftVector, final Map<CharSequence, Integer> rightVector, final Set<CharSequence> intersection) {
-        long dotProduct = 0;
+        double dotProduct = 0;
         for (final CharSequence key : intersection) {
             dotProduct += leftVector.get(key) * (long) rightVector.get(key);
         }
diff --git a/src/test/java/org/apache/commons/text/similarity/CosineSimilarityTest.java b/src/test/java/org/apache/commons/text/similarity/CosineSimilarityTest.java
index 0f95908748..87769405de 100644
--- a/src/test/java/org/apache/commons/text/similarity/CosineSimilarityTest.java
+++ b/src/test/java/org/apache/commons/text/similarity/CosineSimilarityTest.java
@@ -24,9 +24,21 @@
 import java.util.Map;
 
 import org.junit.jupiter.api.Test;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.ValueSource;
 
 class CosineSimilarityTest {
 
+    @ParameterizedTest
+    @ValueSource(ints = {1, Integer.MAX_VALUE, Integer.MIN_VALUE})
+    void testCosineSimilarityOfIdenticalVectors(final int value) {
+        final Map<CharSequence, Integer> vector = new HashMap<>();
+        vector.put("a", value);
+        vector.put("b", value);
+        vector.put("c", value);
+        assertEquals(1.0, CosineSimilarity.INSTANCE.cosineSimilarity(vector, vector), 1e-12);
+    }
+
     @Test
     void testCosineSimilarityReturningDoubleWhereByteValueIsZero() {
         final Map<CharSequence, Integer> hashMap = new HashMap<>();