Fix error in string comparisons with CHAR(31) against the space-padding

of strings of unequal length. (Bug #8134)

mysql-test/r/compare.result

@@ -36,3 +36,6 @@ hex(a)	STRCMP(a,'a')	STRCMP(a,'a ')
 6109	-1	-1
 61	0	0
 DROP TABLE t1;
+SELECT CHAR(31) = '', '' = CHAR(31);
+CHAR(31) = ''	'' = CHAR(31)
+0	0

mysql-test/t/compare.test

@@ -30,3 +30,6 @@ CREATE TABLE t1 (a char(10) not null);
 INSERT INTO t1 VALUES ('a'),('a\0'),('a\t'),('a ');
 SELECT hex(a),STRCMP(a,'a'), STRCMP(a,'a ') FROM t1;
 DROP TABLE t1;
+
+# Bug #8134: Comparison against CHAR(31) at end of string
+SELECT CHAR(31) = '', '' = CHAR(31);

strings/ctype-simple.c

@@ -153,7 +153,7 @@ int my_strnncollsp_simple(CHARSET_INFO * cs, const uchar *a, uint a_length,
       /* put shorter key in s */
       a_length= b_length;
       a= b;
-      swap= -1;					/* swap sign of result */
+      swap= -1^1;				/* swap sign of result */
     }
     for (end= a + a_length-length; a < end ; a++)
     {