*: fix issue#1089 and add tests (pingcap#1106)

session_test.go

@@ -604,6 +604,24 @@ func (s *testSessionSuite) TestIssue986(c *C) {
 	c.Assert(err, IsNil)
 }
 
+func (s *testSessionSuite) TestIssue1089(c *C) {
+	defer testleak.AfterTest(c)()
+	store := newStore(c, s.dbName)
+	se := newSession(c, store, s.dbName)
+
+	r := mustExecSQL(c, se, "select cast(0.5 as unsigned)")
+	row, err := r.Next()
+	c.Assert(err, IsNil)
+	match(c, row.Data, 1)
+	r = mustExecSQL(c, se, "select cast(-0.5 as signed)")
+	row, err = r.Next()
+	c.Assert(err, IsNil)
+	match(c, row.Data, -1)
+
+	err = store.Close()
+	c.Assert(err, IsNil)
+}
+
 func (s *testSessionSuite) TestSelectForUpdate(c *C) {
 	defer testleak.AfterTest(c)()
 	store := newStore(c, s.dbName)

util/types/etc_test.go

@@ -258,12 +258,14 @@ func (s *testTypeEtcSuite) TestRoundFloat(c *C) {
 		Input  float64
 		Expect float64
 	}{
-		{2.5, 2},
+		{2.5, 3},
 		{1.5, 2},
-		{0.5, 0},
+		{0.5, 1},
+		{0.49999999999999997, 0},
 		{0, 0},
-		{-0.5, 0},
-		{-2.5, -2},
+		{-0.49999999999999997, 0},
+		{-0.5, -1},
+		{-2.5, -3},
 		{-1.5, -2},
 	}
 

util/types/helper.go

@@ -20,15 +20,16 @@ import (
 	"github.com/pingcap/tidb/mysql"
 )
 
-// RoundFloat rounds float val to the nearest integer value with float64 format, like GNU rint function.
-// RoundFloat uses default rounding mode, see http://www.gnu.org/software/libc/manual/html_node/Rounding.html
-// so we will choose the even number if the result is midway between two representable value.
-// e.g, 1.5 -> 2, 2.5 -> 2.
+// RoundFloat rounds float val to the nearest integer value with float64 format, like MySQL Round function.
+// RoundFloat uses default rounding mode, see https://dev.mysql.com/doc/refman/5.7/en/precision-math-rounding.html
+// so rounding use "round half away from zero".
+// e.g, 1.5 -> 2, -1.5 -> -2.
 func RoundFloat(f float64) float64 {
-	if math.Remainder(f, 1.0) < 0 {
-		return math.Ceil(f)
+	if math.Abs(f) < 0.5 {
+		return 0
 	}
-	return math.Floor(f)
+
+	return math.Trunc(f + math.Copysign(0.5, f))
 }
 
 func getMaxFloat(flen int, decimal int) float64 {