Fix mul and minus

pingcap · Jul 16, 2019 · ed7413d · ed7413d
1 parent 39624bf
commit ed7413d
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Showing 2 changed files with 14 additions and 7 deletions.
diff --git a/expression/integration_test.go b/expression/integration_test.go
@@ -2839,7 +2839,10 @@ func (s *testIntegrationSuite) TestArithmeticBuiltin(c *C) {
 	c.Assert(err, NotNil)
 	c.Assert(err.Error(), Equals, "[types:1690]BIGINT UNSIGNED value is out of range in '(18446744073709551615 - -1)'")
 	c.Assert(rs.Close(), IsNil)
+	tk.MustQuery(`select cast(-3 as unsigned) - cast(-1 as signed);`).Check(testkit.Rows("18446744073709551614"))
+	tk.MustQuery("select 1.11 - 1.11;").Check(testkit.Rows("0.00"))
 
+	// for multiply
 	tk.MustQuery("select 1234567890 * 1234567890").Check(testkit.Rows("1524157875019052100"))
 	rs, err = tk.Exec("select 1234567890 * 12345671890")
 	c.Assert(err, IsNil)
@@ -2866,8 +2869,7 @@ func (s *testIntegrationSuite) TestArithmeticBuiltin(c *C) {
 	_, err = session.GetRows4Test(ctx, tk.Se, rs)
 	c.Assert(terror.ErrorEqual(err, types.ErrOverflow), IsTrue)
 	c.Assert(rs.Close(), IsNil)
-	result = tk.MustQuery(`select cast(-3 as unsigned) - cast(-1 as signed);`)
-	result.Check(testkit.Rows("18446744073709551614"))
+	tk.MustQuery("select 0.0 * -1;").Check(testkit.Rows("0.0"))
 
 	tk.MustExec("DROP TABLE IF EXISTS t;")
 	tk.MustExec("CREATE TABLE t(a DECIMAL(4, 2), b DECIMAL(5, 3));")

diff --git a/types/mydecimal.go b/types/mydecimal.go
@@ -107,6 +107,13 @@ var (
 	zeroMyDecimal = MyDecimal{}
 )
 
+// get the zero of MyDecimal with the specified result fraction digits
+func zeroMyDecimalWithFrac(frac int8) MyDecimal {
+	zero := MyDecimal{}
+	zero.resultFrac = frac
+	return zero
+}
+
 // add adds a and b and carry, returns the sum and new carry.
 func add(a, b, carry int32) (int32, int32) {
 	sum := a + b + carry
@@ -1556,7 +1563,7 @@ func doSub(from1, from2, to *MyDecimal) (cmp int, err error) {
 				if to == nil {
 					return 0, nil
 				}
-				*to = zeroMyDecimal
+				*to = zeroMyDecimalWithFrac(to.resultFrac)
 				return 0, nil
 			}
 		}
@@ -1911,7 +1918,7 @@ func DecimalMul(from1, from2, to *MyDecimal) error {
 			idx++
 			/* We got decimal zero */
 			if idx == end {
-				*to = zeroMyDecimal
+				*to = zeroMyDecimalWithFrac(to.resultFrac)
 				break
 			}
 		}
@@ -2010,9 +2017,7 @@ func doDivMod(from1, from2, to, mod *MyDecimal, fracIncr int) error {
 	}
 	if prec1 <= 0 {
 		/* short-circuit everything: from1 == 0 */
-		resultFrac := to.resultFrac
-		*to = zeroMyDecimal
-		to.resultFrac = resultFrac
+		*to = zeroMyDecimalWithFrac(to.resultFrac)
 		return nil
 	}
 	prec1 -= countLeadingZeroes((prec1-1)%digitsPerWord, from1.wordBuf[idx1])