From db40730ff05ea6cd491db3cbce7d6fccc61e7c45 Mon Sep 17 00:00:00 2001
From: Sabith Saheb <shabi7204192361@gmail.com>
Date: Wed, 14 Oct 2026 12:40:02 +0530
Subject: [PATCH] Fix != to return true when either operand is NaN

XPath 1.0 section 3.4 compares numbers per IEEE 754, where NaN is not
equal to anything, including itself: '=' with a NaN operand is false
and '!=' is true. CoreOperationCompare.equal returned false early for
NaN before the 'result ^ invert' step that implements '!=', so both
operators answered false. Java's == on doubles already follows
IEEE 754, so the early returns are removed and the comparison result
flows through the inversion. Completes JXPATH-95.
---
 .../jxpath/ri/compiler/CoreOperationCompare.java    | 13 +++----------
 .../jxpath/ri/compiler/CoreOperationTest.java       |  9 ++++++---
 2 files changed, 9 insertions(+), 13 deletions(-)

diff --git a/src/main/java/org/apache/commons/jxpath/ri/compiler/CoreOperationCompare.java b/src/main/java/org/apache/commons/jxpath/ri/compiler/CoreOperationCompare.java
index ba0b9ea2e..0248c38d4 100644
--- a/src/main/java/org/apache/commons/jxpath/ri/compiler/CoreOperationCompare.java
+++ b/src/main/java/org/apache/commons/jxpath/ri/compiler/CoreOperationCompare.java
@@ -137,16 +137,9 @@ protected boolean equal(Object l, Object r) {
         if (l instanceof Boolean || r instanceof Boolean) {
             result = l == r || InfoSetUtil.booleanValue(l) == InfoSetUtil.booleanValue(r);
         } else if (l instanceof Number || r instanceof Number) {
-            // if either side is NaN, no comparison returns true:
-            final double ld = InfoSetUtil.doubleValue(l);
-            if (Double.isNaN(ld)) {
-                return false;
-            }
-            final double rd = InfoSetUtil.doubleValue(r);
-            if (Double.isNaN(rd)) {
-                return false;
-            }
-            result = ld == rd;
+            // Numbers are compared per IEEE 754 (XPath 1.0 section 3.4): NaN is not
+            // equal to anything, including itself, so "=" is false and "!=" is true.
+            result = InfoSetUtil.doubleValue(l) == InfoSetUtil.doubleValue(r);
         } else {
             if (l instanceof String || r instanceof String) {
                 l = InfoSetUtil.stringValue(l);
diff --git a/src/test/java/org/apache/commons/jxpath/ri/compiler/CoreOperationTest.java b/src/test/java/org/apache/commons/jxpath/ri/compiler/CoreOperationTest.java
index 7c47790b3..7e960ca87 100644
--- a/src/test/java/org/apache/commons/jxpath/ri/compiler/CoreOperationTest.java
+++ b/src/test/java/org/apache/commons/jxpath/ri/compiler/CoreOperationTest.java
@@ -105,21 +105,24 @@ void testNan() {
         assertXPathValue(context, "$nan <= $nan", Boolean.FALSE, Boolean.class);
         assertXPathValue(context, "$nan >= $nan and $nan <= $nan", Boolean.FALSE, Boolean.class);
         assertXPathValue(context, "$nan = $nan", Boolean.FALSE, Boolean.class);
-        assertXPathValue(context, "$nan != $nan", Boolean.FALSE, Boolean.class);
+        assertXPathValue(context, "$nan != $nan", Boolean.TRUE, Boolean.class);
         assertXPathValue(context, "$nan > 0", Boolean.FALSE, Boolean.class);
         assertXPathValue(context, "$nan < 0", Boolean.FALSE, Boolean.class);
         assertXPathValue(context, "$nan >= 0", Boolean.FALSE, Boolean.class);
         assertXPathValue(context, "$nan <= 0", Boolean.FALSE, Boolean.class);
         assertXPathValue(context, "$nan >= 0 and $nan <= 0", Boolean.FALSE, Boolean.class);
         assertXPathValue(context, "$nan = 0", Boolean.FALSE, Boolean.class);
-        assertXPathValue(context, "$nan != 0", Boolean.FALSE, Boolean.class);
+        assertXPathValue(context, "$nan != 0", Boolean.TRUE, Boolean.class);
         assertXPathValue(context, "$nan > 1", Boolean.FALSE, Boolean.class);
         assertXPathValue(context, "$nan < 1", Boolean.FALSE, Boolean.class);
         assertXPathValue(context, "$nan >= 1", Boolean.FALSE, Boolean.class);
         assertXPathValue(context, "$nan <= 1", Boolean.FALSE, Boolean.class);
         assertXPathValue(context, "$nan >= 1 and $nan <= 1", Boolean.FALSE, Boolean.class);
         assertXPathValue(context, "$nan = 1", Boolean.FALSE, Boolean.class);
-        assertXPathValue(context, "$nan != 1", Boolean.FALSE, Boolean.class);
+        assertXPathValue(context, "$nan != 1", Boolean.TRUE, Boolean.class);
+        assertXPathValue(context, "number('foo') = 1", Boolean.FALSE, Boolean.class);
+        assertXPathValue(context, "number('foo') != 1", Boolean.TRUE, Boolean.class);
+        assertXPathValue(context, "number('foo') != number('foo')", Boolean.TRUE, Boolean.class);
     }
 
     @Test