From ded5bc966345e063c9a125a232952d1994e29425 Mon Sep 17 00:00:00 2001
From: Todd White <todd.white@thalion.global>
Date: Sun, 28 Jun 2026 15:32:33 -0400
Subject: [PATCH] CFString: fix range in
 CFStringGetSurrogatePairForLongCharacter

The function rejected characters greater than U+10000 (returning false)
and produced a surrogate pair for everything up to and including U+10000,
including BMP characters.  The comparison was inverted: a surrogate pair
is needed for supplementary-plane characters (>= U+10000), while BMP
characters (< U+10000) need none, so nearly the whole supplementary
plane (U+10001..U+10FFFF) was wrongly rejected.

Use "character < 0x10000".

Add Tests/CFString/surrogate.m.
---
 Source/CFString.c          |  2 +-
 Tests/CFString/surrogate.m | 24 ++++++++++++++++++++++++
 2 files changed, 25 insertions(+), 1 deletion(-)
 create mode 100644 Tests/CFString/surrogate.m

diff --git a/Source/CFString.c b/Source/CFString.c
index cbd67b8c..6d012cdc 100644
--- a/Source/CFString.c
+++ b/Source/CFString.c
@@ -935,7 +935,7 @@ Boolean
 CFStringGetSurrogatePairForLongCharacter (UTF32Char character,
                                           UniChar * surrogates)
 {
-  if (character > 0x10000)
+  if (character < 0x10000)
     return false;
 
   surrogates[0] = U16_LEAD (character);
diff --git a/Tests/CFString/surrogate.m b/Tests/CFString/surrogate.m
new file mode 100644
index 00000000..dec2cece
--- /dev/null
+++ b/Tests/CFString/surrogate.m
@@ -0,0 +1,24 @@
+#include "CoreFoundation/CFString.h"
+#include "../CFTesting.h"
+
+/* CFStringGetSurrogatePairForLongCharacter for supplementary-plane and BMP characters. */
+
+int main (void)
+{
+  UniChar pair[2];
+
+  PASS_CF(CFStringGetSurrogatePairForLongCharacter(0x1F600, pair) == true,
+    "Supplementary character U+1F600 yields a surrogate pair.");
+  PASS_CF(pair[0] == 0xD83D && pair[1] == 0xDE00,
+    "Surrogate pair for U+1F600 is D83D DE00.");
+  PASS_CF(CFStringGetLongCharacterForSurrogatePair(pair[0], pair[1]) == 0x1F600,
+    "Surrogate pair round-trips back to U+1F600.");
+
+  PASS_CF(CFStringGetSurrogatePairForLongCharacter(0x10000, pair) == true,
+    "The first supplementary character U+10000 yields a pair.");
+
+  PASS_CF(CFStringGetSurrogatePairForLongCharacter(0x0041, pair) == false,
+    "A BMP character (U+0041) yields no surrogate pair.");
+
+  return 0;
+}