Index: include/string
===================================================================
--- include/string	(revision 213127)
+++ include/string	(working copy)
@@ -646,7 +646,14 @@
 
     _LIBCPP_INLINE_VISIBILITY
     static int compare(const char_type* __s1, const char_type* __s2, size_t __n)
-        {return memcmp(__s1, __s2, __n);}
+        {
+            if (!__n) return 0;
+            while (--__n && *__s1 == *__s2) {
+                ++__s1;
+                ++__s2;
+            }
+            return *__s1 - *__s2;
+        }
     _LIBCPP_INLINE_VISIBILITY
     static size_t length(const char_type* __s) {return strlen(__s);}
     _LIBCPP_INLINE_VISIBILITY
@@ -705,7 +712,15 @@
 
     _LIBCPP_INLINE_VISIBILITY
     static int compare(const char_type* __s1, const char_type* __s2, size_t __n)
-        {return wmemcmp(__s1, __s2, __n);}
+        {
+            if (!__n) return 0;
+            while (--__n && *__s1 == *__s2) {
+                ++__s1;
+                ++__s2;
+            }
+            // wchar_t might be unsigned
+            return *__s1 == *__s2 ? 0 : *__s1 > *__s2 ? 1 : -1;
+        }
     _LIBCPP_INLINE_VISIBILITY
     static size_t length(const char_type* __s)
         {return wcslen(__s);}