MDEV-17256 Decimal field multiplication bug.bb-5.5-hf

We should clear trailing zeroes in frac part. Otherwise
that tail is growing quickly and forces unnecessary truncating of
arguments.

3 files changed, 105 insertions, 16 deletions

diff --git a/mysql-test/r/type_newdecimal.result b/mysql-test/r/type_newdecimal.result
index 3cd5028f858..81d1637947c 100644
--- a/mysql-test/r/type_newdecimal.result
+++ b/mysql-test/r/type_newdecimal.result
@@ -1997,3 +1997,45 @@ select 0.0000000001 mod 1;
 select 0.01 mod 1;
 0.01 mod 1
 0.01
+CREATE TABLE t1 (
+`FLD1` decimal(7,4) unsigned zerofill NOT NULL DEFAULT 001.0000,
+`FLD2` decimal(7,4) unsigned zerofill NOT NULL DEFAULT 001.0000,
+`FLD3` decimal(7,4) unsigned zerofill NOT NULL DEFAULT 001.0000,
+`FLD4` decimal(7,4) unsigned zerofill NOT NULL DEFAULT 001.0000,
+`FLD5` decimal(7,4) unsigned zerofill NOT NULL DEFAULT 001.0000,
+`FLD6` decimal(7,4) unsigned zerofill NOT NULL DEFAULT 001.0000,
+`FLD7` decimal(7,4) unsigned zerofill NOT NULL DEFAULT 001.0000,
+`FLD8` decimal(7,4) unsigned zerofill NOT NULL DEFAULT 001.0000,
+`FLD9` decimal(7,4) unsigned zerofill NOT NULL DEFAULT 001.0000,
+`FLD10` decimal(7,4) unsigned zerofill NOT NULL DEFAULT 001.0000,
+`FLD11` decimal(7,4) unsigned zerofill NOT NULL DEFAULT 001.0000,
+`FLD12` decimal(7,4) unsigned zerofill NOT NULL DEFAULT 001.0000,
+`FLD13` decimal(7,4) unsigned zerofill NOT NULL DEFAULT 001.0000,
+`FLD14` decimal(7,4) unsigned zerofill NOT NULL DEFAULT 001.0000,
+`FLD15` decimal(7,4) unsigned zerofill NOT NULL DEFAULT 001.0000,
+`FLD16` decimal(7,4) unsigned zerofill NOT NULL DEFAULT 001.0000,
+`FLD17` decimal(7,4) unsigned zerofill NOT NULL DEFAULT 001.0000,
+`FLD18` decimal(7,4) unsigned zerofill NOT NULL DEFAULT 001.0000,
+`FLD19` decimal(7,4) unsigned zerofill NOT NULL DEFAULT 001.0000,
+`FLD20` decimal(7,4) unsigned zerofill NOT NULL DEFAULT 001.0000,
+`FLD21` decimal(7,4) unsigned zerofill NOT NULL DEFAULT 001.0000,
+`FLD22` decimal(7,4) unsigned zerofill NOT NULL DEFAULT 001.0000,
+`FLD23` decimal(7,4) unsigned zerofill NOT NULL DEFAULT 001.0000
+);
+INSERT INTO t1 VALUES (001.0760,000.9500,001.0000,001.0000,001.0000,
+001.0000,001.0000,001.0000,001.0000,001.0000,001.0000,000.5949,001.0194,
+001.0000,001.0000,001.0000,001.0000,001.0000,001.0000,000.9220,001.1890,001.2130,327.2690);
+select FLD1*FLD2*FLD3*FLD4*FLD5*FLD6*FLD7*FLD8*FLD9*FLD10*FLD11*FLD12*FLD13*FLD14*FLD15*FLD16*FLD17*FLD18*FLD19*FLD20*FLD21*FLD22*FLD23 as calc1 from t1;
+calc1
+269.775757576440530322187032000000
+select FLD23*FLD2*FLD1*FLD4*FLD5*FLD11*FLD12*FLD13*FLD3*FLD15*FLD16*FLD17*FLD18*FLD19*FLD20*FLD21*FLD22*FLD14*FLD6*FLD7*FLD8*FLD9*FLD10 as calc2 from t1;
+calc2
+269.775757576440530322187032000000
+DROP TABLE t1;
+CREATE TABLE t1 AS SELECT 1.0 * 2.000;
+SHOW CREATE TABLE t1;
+Table	Create Table
+t1	CREATE TABLE `t1` (
+  `1.0 * 2.000` decimal(6,4) NOT NULL DEFAULT '0.0000'
+) ENGINE=MyISAM DEFAULT CHARSET=latin1
+DROP TABLE t1;
diff --git a/mysql-test/t/type_newdecimal.test b/mysql-test/t/type_newdecimal.test
index bb5a61d84ec..adc8eb77198 100644
--- a/mysql-test/t/type_newdecimal.test
+++ b/mysql-test/t/type_newdecimal.test
@@ -1581,3 +1581,47 @@ select 0.000000000000000000000000000000000000000000000000001 mod 1;
 select 0.0000000001 mod 1;
 select 0.01 mod 1;
 
+#
+# MDEV-17256 Decimal field multiplication bug
+#
+
+CREATE TABLE t1 (
+    `FLD1` decimal(7,4) unsigned zerofill NOT NULL DEFAULT 001.0000,
+    `FLD2` decimal(7,4) unsigned zerofill NOT NULL DEFAULT 001.0000,
+    `FLD3` decimal(7,4) unsigned zerofill NOT NULL DEFAULT 001.0000,
+    `FLD4` decimal(7,4) unsigned zerofill NOT NULL DEFAULT 001.0000,
+    `FLD5` decimal(7,4) unsigned zerofill NOT NULL DEFAULT 001.0000,
+    `FLD6` decimal(7,4) unsigned zerofill NOT NULL DEFAULT 001.0000,
+    `FLD7` decimal(7,4) unsigned zerofill NOT NULL DEFAULT 001.0000,
+    `FLD8` decimal(7,4) unsigned zerofill NOT NULL DEFAULT 001.0000,
+    `FLD9` decimal(7,4) unsigned zerofill NOT NULL DEFAULT 001.0000,
+    `FLD10` decimal(7,4) unsigned zerofill NOT NULL DEFAULT 001.0000,
+    `FLD11` decimal(7,4) unsigned zerofill NOT NULL DEFAULT 001.0000,
+    `FLD12` decimal(7,4) unsigned zerofill NOT NULL DEFAULT 001.0000,
+    `FLD13` decimal(7,4) unsigned zerofill NOT NULL DEFAULT 001.0000,
+    `FLD14` decimal(7,4) unsigned zerofill NOT NULL DEFAULT 001.0000,
+    `FLD15` decimal(7,4) unsigned zerofill NOT NULL DEFAULT 001.0000,
+    `FLD16` decimal(7,4) unsigned zerofill NOT NULL DEFAULT 001.0000,
+    `FLD17` decimal(7,4) unsigned zerofill NOT NULL DEFAULT 001.0000,
+    `FLD18` decimal(7,4) unsigned zerofill NOT NULL DEFAULT 001.0000,
+    `FLD19` decimal(7,4) unsigned zerofill NOT NULL DEFAULT 001.0000,
+    `FLD20` decimal(7,4) unsigned zerofill NOT NULL DEFAULT 001.0000,
+    `FLD21` decimal(7,4) unsigned zerofill NOT NULL DEFAULT 001.0000,
+    `FLD22` decimal(7,4) unsigned zerofill NOT NULL DEFAULT 001.0000,
+    `FLD23` decimal(7,4) unsigned zerofill NOT NULL DEFAULT 001.0000
+);
+     
+INSERT INTO t1 VALUES (001.0760,000.9500,001.0000,001.0000,001.0000,
+    001.0000,001.0000,001.0000,001.0000,001.0000,001.0000,000.5949,001.0194,
+    001.0000,001.0000,001.0000,001.0000,001.0000,001.0000,000.9220,001.1890,001.2130,327.2690);
+     
+select FLD1*FLD2*FLD3*FLD4*FLD5*FLD6*FLD7*FLD8*FLD9*FLD10*FLD11*FLD12*FLD13*FLD14*FLD15*FLD16*FLD17*FLD18*FLD19*FLD20*FLD21*FLD22*FLD23 as calc1 from t1;
+select FLD23*FLD2*FLD1*FLD4*FLD5*FLD11*FLD12*FLD13*FLD3*FLD15*FLD16*FLD17*FLD18*FLD19*FLD20*FLD21*FLD22*FLD14*FLD6*FLD7*FLD8*FLD9*FLD10 as calc2 from t1;
+     
+DROP TABLE t1;
+
+CREATE TABLE t1 AS SELECT 1.0 * 2.000;
+SHOW CREATE TABLE t1;
+DROP TABLE t1;
+
+
diff --git a/strings/decimal.c b/strings/decimal.c
index 3d90a58ea8a..05546aa77a3 100644
--- a/strings/decimal.c
+++ b/strings/decimal.c
@@ -2077,26 +2077,21 @@ int decimal_mul(const decimal_t *from1, const decimal_t *from2, decimal_t *to)
     }
   }
 
-  /* Now we have to check for -0.000 case */
-  if (to->sign)
+  /* Remove trailing zero words in frac part */
+  frac0= ROUND_UP(to->frac);
+
+  if (frac0 > 0 && to->buf[intg0 + frac0 - 1] == 0)
   {
-    dec1 *buf= to->buf;
-    dec1 *end= to->buf + intg0 + frac0;
-    DBUG_ASSERT(buf != end);
-    for (;;)
+    do
     {
-      if (*buf)
-        break;
-      if (++buf == end)
-      {
-        /* We got decimal zero */
-        decimal_make_zero(to);
-        break;
-      }
-    }
+      frac0--;
+    } while (frac0 > 0 && to->buf[intg0 + frac0 - 1] == 0);
+    to->frac= DIG_PER_DEC1 * frac0;
   }
+
+  /* Remove heading zero words in intg part */
   buf1= to->buf;
-  d_to_move= intg0 + ROUND_UP(to->frac);
+  d_to_move= intg0 + frac0;
   while (!*buf1 && (to->intg > DIG_PER_DEC1))
   {
     buf1++;
@@ -2109,6 +2104,14 @@ int decimal_mul(const decimal_t *from1, const decimal_t *from2, decimal_t *to)
     for (; d_to_move--; cur_d++, buf1++)
       *cur_d= *buf1;
   }
+
+  /* Now we have to check for -0.000 case */
+  if (to->sign && to->frac == 0 && to->buf[0] == 0)
+  {
+    DBUG_ASSERT(to->intg <= DIG_PER_DEC1);
+    /* We got decimal zero */
+    decimal_make_zero(to);
+  }
   return error;
 }