Fix for bug #12938 (decimal arithmetic in the loop fails)

mysql-test/r/type_newdecimal.result:
  test result fixed
mysql-test/t/type_newdecimal.test:
  test case added
strings/decimal.c:
  code to cut heading zeroes off the result of the multiplication added

mysql-test/r/type_newdecimal.result

@@ -984,3 +984,35 @@ t1	CREATE TABLE `t1` (
   `f1` decimal(10,0) unsigned zerofill NOT NULL default '0000000000'
 ) ENGINE=MyISAM DEFAULT CHARSET=latin1
 drop table t1;
+drop procedure if exists wg2;
+Warnings:
+Note	1305	PROCEDURE wg2 does not exist
+create procedure wg2()
+begin
+declare v int default 1;
+declare tdec decimal(5) default 0;
+while v <= 9 do set tdec =tdec * 10;
+select v, tdec;
+set v = v + 1;
+end while;
+end//
+call wg2()//
+v	tdec
+1	0
+v	tdec
+2	0
+v	tdec
+3	0
+v	tdec
+4	0
+v	tdec
+5	0
+v	tdec
+6	0
+v	tdec
+7	0
+v	tdec
+8	0
+v	tdec
+9	0
+drop procedure wg2;

mysql-test/t/type_newdecimal.test

@@ -1015,3 +1015,25 @@ create table t1 (
         f1 decimal (0,0) zerofill not null default 0);
 show create table t1;
 drop table t1;
+
+#
+# Bug 12938 (arithmetic loop's zero)
+#
+--disable-warnings
+drop procedure if exists wg2;
+--enable-warnings
+delimiter //;
+create procedure wg2()
+begin
+  declare v int default 1;
+  declare tdec decimal(5) default 0;
+  while v <= 9 do set tdec =tdec * 10;
+    select v, tdec;
+    set v = v + 1;
+  end while;
+end//
+
+call wg2()//
+
+delimiter ;//
+drop procedure wg2;

strings/decimal.c

@@ -1933,7 +1933,7 @@ int decimal_mul(decimal_t *from1, decimal_t *from2, decimal_t *to)
   int intg1=ROUND_UP(from1->intg), intg2=ROUND_UP(from2->intg),
       frac1=ROUND_UP(from1->frac), frac2=ROUND_UP(from2->frac),
       intg0=ROUND_UP(from1->intg+from2->intg),
-      frac0=frac1+frac2, error, i, j;
+      frac0=frac1+frac2, error, i, j, d_to_move;
   dec1 *buf1=from1->buf+intg1, *buf2=from2->buf+intg2, *buf0,
        *start2, *stop2, *stop1, *start0, carry;
 
@@ -2007,6 +2007,20 @@ int decimal_mul(decimal_t *from1, decimal_t *from2, decimal_t *to)
       }
     }
   }
+  buf1= to->buf;
+  d_to_move= intg0 + ROUND_UP(to->frac);
+  while (!*buf1 && (to->intg > DIG_PER_DEC1))
+  {
+    buf1++;
+    to->intg-= DIG_PER_DEC1;
+    d_to_move--;
+  }
+  if (to->buf < buf1)
+  {
+    dec1 *cur_d= to->buf;
+    for (; d_to_move; d_to_move--, cur_d++, buf1++)
+      *cur_d= *buf1;
+  }
   return error;
 }