From ea86cd59c81b78f2ffe153b7882b5834d36a5db3 Mon Sep 17 00:00:00 2001
From: Willi Ballenthin <wballenthin@hex-rays.com>
Date: Tue, 24 Mar 2026 09:11:35 +0100
Subject: [PATCH] fix Median operation returns incorrect result for unsorted
 odd-length inputs

closes #2239
---
 src/core/lib/Arithmetic.mjs       | 13 +++++++-----
 tests/operations/index.mjs        |  1 +
 tests/operations/tests/Median.mjs | 33 +++++++++++++++++++++++++++++++
 3 files changed, 42 insertions(+), 5 deletions(-)
 create mode 100644 tests/operations/tests/Median.mjs

diff --git a/src/core/lib/Arithmetic.mjs b/src/core/lib/Arithmetic.mjs
index 7c10855f..5fbc5771 100644
--- a/src/core/lib/Arithmetic.mjs
+++ b/src/core/lib/Arithmetic.mjs
@@ -108,14 +108,17 @@ export function mean(data) {
  * @returns {BigNumber}
  */
 export function median(data) {
-    if ((data.length % 2) === 0 && data.length > 0) {
+    if (data.length > 0) {
         data.sort(function(a, b) {
             return a.minus(b);
         });
-        const first = data[Math.floor(data.length / 2)];
-        const second = data[Math.floor(data.length / 2) - 1];
-        return mean([first, second]);
-    } else {
+
+        if ((data.length % 2) === 0) {
+            const first = data[Math.floor(data.length / 2)];
+            const second = data[Math.floor(data.length / 2) - 1];
+            return mean([first, second]);
+        }
+
         return data[Math.floor(data.length / 2)];
     }
 }
diff --git a/tests/operations/index.mjs b/tests/operations/index.mjs
index f030349d..98631405 100644
--- a/tests/operations/index.mjs
+++ b/tests/operations/index.mjs
@@ -111,6 +111,7 @@ import "./tests/LuhnChecksum.mjs";
 import "./tests/LZNT1Decompress.mjs";
 import "./tests/LZString.mjs";
 import "./tests/Magic.mjs";
+import "./tests/Median.mjs";
 import "./tests/Media.mjs";
 import "./tests/MIMEDecoding.mjs";
 import "./tests/Modhex.mjs";
diff --git a/tests/operations/tests/Median.mjs b/tests/operations/tests/Median.mjs
new file mode 100644
index 00000000..555f2edd
--- /dev/null
+++ b/tests/operations/tests/Median.mjs
@@ -0,0 +1,33 @@
+/**
+ * Median operation tests.
+ *
+ * @author copilot-swe-agent[bot]
+ * @copyright Crown Copyright 2018
+ * @license Apache-2.0
+ */
+import TestRegister from "../../lib/TestRegister.mjs";
+
+TestRegister.addTests([
+    {
+        name: "Median: odd-length input",
+        input: "10 1 2",
+        expectedOutput: "2",
+        recipeConfig: [
+            {
+                op: "Median",
+                args: ["Space"],
+            },
+        ],
+    },
+    {
+        name: "Median: even-length input",
+        input: "10 1 2 5",
+        expectedOutput: "3.5",
+        recipeConfig: [
+            {
+                op: "Median",
+                args: ["Space"],
+            },
+        ],
+    },
+]);