# HG changeset patch
# User Bruno Haible <bruno@clisp.org>
# Date 1552073902 -3600
# Node ID 5f58d2ac35ea2fc31ccc90cb6d21b8327ce30986
# Parent  44073ad4207fa948b0465c2133820d26ee8b604b
unistr/u8-cmp: Fix undefined behaviour.

Reported by Jeffrey Walton <noloader@gmail.com>.

* lib/unistr/u8-cmp.c (u8_cmp): Don't invoke memcmp if n is zero.

diff -r 44073ad4207f -r 5f58d2ac35ea ChangeLog
--- a/ChangeLog	Fri Mar 08 19:17:37 2019 +0100
+++ b/ChangeLog	Fri Mar 08 20:38:22 2019 +0100
@@ -1,3 +1,9 @@
+2019-03-08  Bruno Haible  <bruno@clisp.org>
+
+	unistr/u8-cmp: Fix undefined behaviour.
+	Reported by Jeffrey Walton <noloader@gmail.com>.
+	* lib/unistr/u8-cmp.c (u8_cmp): Don't invoke memcmp if n is zero.
+
 2019-03-08  Bruno Haible  <bruno@clisp.org>
 
 	unictype/numeric: Fix undefined behaviour.
diff -r 44073ad4207f -r 5f58d2ac35ea lib/unistr/u8-cmp.c
--- a/lib/unistr/u8-cmp.c	Fri Mar 08 19:17:37 2019 +0100
+++ b/lib/unistr/u8-cmp.c	Fri Mar 08 20:38:22 2019 +0100
@@ -26,5 +26,5 @@
 u8_cmp (const uint8_t *s1, const uint8_t *s2, size_t n)
 {
   /* Use the fact that the UTF-8 encoding preserves lexicographic order.  */
-  return memcmp ((const char *) s1, (const char *) s2, n);
+  return n == 0 ? 0 : memcmp ((const char *) s1, (const char *) s2, n);
 }