Bug#15811: extremely long time for mysql client to execute long INSERT

The problem was in redundant calls to strlen() in string functions,
where we may then return after checking only the small number of characters.

No test case is provided since it's a performance fix.

strings/ctype-mb.c

@@ -24,12 +24,12 @@
 void my_caseup_str_mb(CHARSET_INFO * cs, char *str)
 {
   register uint32 l;
-  register char *end=str+strlen(str); /* BAR TODO: remove strlen() call */
   register uchar *map=cs->to_upper;
   
   while (*str)
   {
-    if ((l=my_ismbchar(cs, str,end)))
+    /* Pointing after the '\0' is safe here. */
+    if ((l=my_ismbchar(cs, str, str + cs->mbmaxlen)))
       str+=l;
     else
     { 
@@ -42,12 +42,12 @@ void my_caseup_str_mb(CHARSET_INFO * cs, char *str)
 void my_casedn_str_mb(CHARSET_INFO * cs, char *str)
 {
   register uint32 l;
-  register char *end=str+strlen(str);
   register uchar *map=cs->to_lower;
   
   while (*str)
   {
-    if ((l=my_ismbchar(cs, str,end)))
+    /* Pointing after the '\0' is safe here. */
+    if ((l=my_ismbchar(cs, str, str + cs->mbmaxlen)))
       str+=l;
     else
     {
@@ -101,15 +101,18 @@ uint my_casedn_mb(CHARSET_INFO * cs, char *src, uint srclen,
   return srclen;
 }
 
+/*
+  my_strcasecmp_mb() returns 0 if strings are equal, non-zero otherwise.
+ */
 int my_strcasecmp_mb(CHARSET_INFO * cs,const char *s, const char *t)
 {
   register uint32 l;
-  register const char *end=s+strlen(s);
   register uchar *map=cs->to_upper;
   
-  while (s<end)
+  while (*s && *t)
   {
-    if ((l=my_ismbchar(cs, s,end)))
+    /* Pointing after the '\0' is safe here. */
+    if ((l=my_ismbchar(cs, s, s + cs->mbmaxlen)))
     {
       while (l--)
         if (*s++ != *t++) 
@@ -120,7 +123,8 @@ int my_strcasecmp_mb(CHARSET_INFO * cs,const char *s, const char *t)
     else if (map[(uchar) *s++] != map[(uchar) *t++])
       return 1;
   }
-  return *t;
+  /* At least one of '*s' and '*t' is zero here. */
+  return (*t != *s);
 }