two bugs in ft_update

myisam/ft_update.c:
  two bugfixes
mysql-test/r/fulltext.result:
  new tests
mysql-test/t/fulltext.test:
  new tests

myisam/ft_update.c

@@ -164,41 +164,35 @@ int _mi_ft_update(MI_INFO *info, uint keynr, byte *keybuf,
   int error= -1;
   FT_WORD *oldlist,*newlist, *old_word, *new_word;
   uint key_length;
-  int cmp;
+  int cmp, cmp2;
 
   if (!(old_word=oldlist=_mi_ft_parserecord(info, keynr, keybuf, oldrec)))
     goto err0;
   if (!(new_word=newlist=_mi_ft_parserecord(info, keynr, keybuf, newrec)))
     goto err1;
 
+  error=0;
   while(old_word->pos && new_word->pos)
   {
     cmp=_mi_compare_text(default_charset_info,
 	                 (uchar*) old_word->pos,old_word->len,
 			 (uchar*) new_word->pos,new_word->len,0);
-    if (cmp==0)
-      cmp=sgn(old_word->weight-new_word->weight);
-    else
-      cmp=sgn(cmp);
+    cmp2= cmp ? 0 : (abs(old_word->weight - new_word->weight) > 1.e-5);
 
-    switch (cmp) {
-    case -1:
+    if (cmp < 0 || cmp2)
+    {
       key_length=_ft_make_key(info,keynr,keybuf,old_word,pos);
       if ((error=_mi_ck_delete(info,keynr,(uchar*) keybuf,key_length)))
         goto err2;
-      old_word++;
-      break;
-    case 0:
-      old_word++;
-      new_word++;
-      break;
-    case 1:
+    }
+    if (cmp > 0 || cmp2)
+    {
       key_length=_ft_make_key(info,keynr,keybuf,new_word,pos);
       if ((error=_mi_ck_write(info,keynr,(uchar*) keybuf,key_length)))
         goto err2;
-      new_word++;
-      break;
-   }
+    }
+    if (cmp<=0) old_word++;
+    if (cmp>=0) new_word++;
  }
  if (old_word->pos)
    error=_mi_ft_erase(info,keynr,keybuf,old_word,pos);

mysql-test/r/fulltext.result

@@ -112,3 +112,19 @@ Can't find FULLTEXT index matching the column list
 select * from t2,t3 where MATCH (t2.inhalt,t3.inhalt) AGAINST ('foobar');
 Wrong arguments to MATCH
 drop table t1,t2,t3;
+CREATE TABLE t1 (
+id int(11)  auto_increment,
+title varchar(100)  default '',
+PRIMARY KEY  (id),
+KEY ind5 (title),
+FULLTEXT KEY FT1 (title)
+) TYPE=MyISAM;
+insert into t1 (title) values ('this is a test');
+update t1 set title='this is A test' where id=1;
+check table t1;
+Table	Op	Msg_type	Msg_text
+test.t1	check	status	OK
+update t1 set title='this test once revealed a bug' where id=1;
+select * from t1;
+id	title
+1	this test once revealed a bug

mysql-test/t/fulltext.test

@@ -92,3 +92,22 @@ select * from t2 where MATCH ticket AGAINST ('foobar');
 select * from t2,t3 where MATCH (t2.inhalt,t3.inhalt) AGAINST ('foobar');
 
 drop table t1,t2,t3;
+
+#
+# two more bugtests
+#
+
+CREATE TABLE t1 (
+  id int(11)  auto_increment,
+  title varchar(100)  default '',
+  PRIMARY KEY  (id),
+  KEY ind5 (title),
+  FULLTEXT KEY FT1 (title)
+) TYPE=MyISAM;
+
+insert into t1 (title) values ('this is a test');
+update t1 set title='this is A test' where id=1;
+check table t1;
+update t1 set title='this test once revealed a bug' where id=1;
+select * from t1;
+