expression/types: fix decimal minus/round/multiple result

expression/aggregation/avg.go

@@ -14,6 +14,7 @@
 package aggregation
 
 import (
+	"github.com/cznic/mathutil"
 	"github.com/juju/errors"
 	"github.com/pingcap/tidb/mysql"
 	"github.com/pingcap/tidb/sessionctx/stmtctx"
@@ -84,7 +85,7 @@ func (af *avgFunction) GetResult(evalCtx *AggEvaluateContext) (d types.Datum) {
 		if frac == -1 {
 			frac = mysql.MaxDecimalScale
 		}
-		err = to.Round(to, frac, types.ModeHalfEven)
+		err = to.Round(to, mathutil.Min(frac, mysql.MaxDecimalScale), types.ModeHalfEven)
 		terror.Log(errors.Trace(err))
 		d.SetMysqlDecimal(to)
 	}

expression/builtin_arithmetic.go

@@ -21,6 +21,7 @@ import (
 	"github.com/juju/errors"
 	"github.com/pingcap/tidb/mysql"
 	"github.com/pingcap/tidb/sessionctx"
+	"github.com/pingcap/tidb/terror"
 	"github.com/pingcap/tidb/types"
 	"github.com/pingcap/tipb/go-tipb"
 )
@@ -523,7 +524,7 @@ func (s *builtinArithmeticMultiplyDecimalSig) evalDecimal(row types.Row) (*types
 	}
 	c := &types.MyDecimal{}
 	err = types.DecimalMul(a, b, c)
-	if err != nil {
+	if err != nil && !terror.ErrorEqual(err, types.ErrTruncated) {
 		return nil, true, errors.Trace(err)
 	}
 	return c, false, nil

expression/builtin_math.go

@@ -26,6 +26,7 @@ import (
 	"strings"
 	"time"
 
+	"github.com/cznic/mathutil"
 	"github.com/juju/errors"
 	"github.com/pingcap/tidb/mysql"
 	"github.com/pingcap/tidb/sessionctx"
@@ -263,8 +264,10 @@ func (c *roundFunctionClass) getFunction(ctx sessionctx.Context, args []Expressi
 	if mysql.HasUnsignedFlag(argFieldTp.Flag) {
 		bf.tp.Flag |= mysql.UnsignedFlag
 	}
+
 	bf.tp.Flen = argFieldTp.Flen
-	bf.tp.Decimal = 0
+	bf.tp.Decimal = calculateDecimal4RoundAndTruncate(ctx, args, argTp)
+
 	var sig builtinFunc
 	if len(args) > 1 {
 		switch argTp {
@@ -292,6 +295,25 @@ func (c *roundFunctionClass) getFunction(ctx sessionctx.Context, args []Expressi
 	return sig, nil
 }
 
+// calculateDecimal4RoundAndTruncate calculates tp.decimals of round/truncate func.
+func calculateDecimal4RoundAndTruncate(ctx sessionctx.Context, args []Expression, retType types.EvalType) int {
+	if retType == types.ETInt || len(args) <= 1 {
+		return 0
+	}
+	secondConst, secondIsConst := args[1].(*Constant)
+	if !secondIsConst {
+		return args[0].GetType().Decimal
+	}
+	argDec, isNull, err := secondConst.EvalInt(ctx, nil)
+	if err != nil || isNull || argDec < 0 {
+		return 0
+	}
+	if argDec > mysql.MaxDecimalScale {
+		return mysql.MaxDecimalScale
+	}
+	return int(argDec)
+}
+
 type builtinRoundRealSig struct {
 	baseBuiltinFunc
 }
@@ -422,7 +444,7 @@ func (b *builtinRoundWithFracDecSig) evalDecimal(row types.Row) (*types.MyDecima
 		return nil, isNull, errors.Trace(err)
 	}
 	to := new(types.MyDecimal)
-	if err = val.Round(to, int(frac), types.ModeHalfEven); err != nil {
+	if err = val.Round(to, mathutil.Min(int(frac), b.tp.Decimal), types.ModeHalfEven); err != nil {
 		return nil, true, errors.Trace(err)
 	}
 	return to, false, nil
@@ -1695,22 +1717,6 @@ type truncateFunctionClass struct {
 	baseFunctionClass
 }
 
-// getDecimal returns the `Decimal` value of return type for function `TRUNCATE`.
-func (c *truncateFunctionClass) getDecimal(ctx sessionctx.Context, arg Expression) int {
-	if constant, ok := arg.(*Constant); ok {
-		decimal, isNull, err := constant.EvalInt(ctx, nil)
-		if isNull || err != nil {
-			return 0
-		} else if decimal > 30 {
-			return 30
-		} else if decimal < 0 {
-			return 0
-		}
-		return int(decimal)
-	}
-	return 3
-}
-
 func (c *truncateFunctionClass) getFunction(ctx sessionctx.Context, args []Expression) (builtinFunc, error) {
 	if err := c.verifyArgs(args); err != nil {
 		return nil, errors.Trace(err)
@@ -1723,11 +1729,7 @@ func (c *truncateFunctionClass) getFunction(ctx sessionctx.Context, args []Expre
 
 	bf := newBaseBuiltinFuncWithTp(ctx, args, argTp, argTp, types.ETInt)
 
-	if argTp == types.ETInt {
-		bf.tp.Decimal = 0
-	} else {
-		bf.tp.Decimal = c.getDecimal(bf.ctx, args[1])
-	}
+	bf.tp.Decimal = calculateDecimal4RoundAndTruncate(ctx, args, argTp)
 	bf.tp.Flen = args[0].GetType().Flen - args[0].GetType().Decimal + bf.tp.Decimal
 	bf.tp.Flag |= args[0].GetType().Flag
 
@@ -1768,7 +1770,7 @@ func (b *builtinTruncateDecimalSig) evalDecimal(row types.Row) (*types.MyDecimal
 	}
 
 	result := new(types.MyDecimal)
-	if err := x.Round(result, int(d), types.ModeTruncate); err != nil {
+	if err := x.Round(result, mathutil.Min(int(d), b.getRetTp().Decimal), types.ModeTruncate); err != nil {
 		return nil, true, errors.Trace(err)
 	}
 	return result, false, nil

expression/builtin_op.go

@@ -749,15 +749,11 @@ func (b *builtinUnaryMinusDecimalSig) Clone() builtinFunc {
 }
 
 func (b *builtinUnaryMinusDecimalSig) evalDecimal(row types.Row) (*types.MyDecimal, bool, error) {
-	var dec *types.MyDecimal
 	dec, isNull, err := b.args[0].EvalDecimal(b.ctx, row)
 	if err != nil || isNull {
 		return dec, isNull, errors.Trace(err)
 	}
-
-	to := new(types.MyDecimal)
-	err = types.DecimalSub(new(types.MyDecimal), dec, to)
-	return to, err != nil, errors.Trace(err)
+	return types.DecimalNeg(dec), false, nil
 }
 
 type builtinUnaryMinusRealSig struct {

expression/integration_test.go

@@ -3352,7 +3352,7 @@ func newStoreWithBootstrap() (kv.Storage, *domain.Domain, error) {
 	return store, dom, errors.Trace(err)
 }
 
-func (s *testIntegrationSuite) TestTwoDecimalAssignTruncate(c *C) {
+func (s *testIntegrationSuite) TestTwoDecimalTruncate(c *C) {
 	tk := testkit.NewTestKit(c, s.store)
 	defer s.cleanEnv(c)
 	tk.MustExec("use test")
@@ -3363,4 +3363,6 @@ func (s *testIntegrationSuite) TestTwoDecimalAssignTruncate(c *C) {
 	tk.MustExec("update t1 set b = a")
 	res := tk.MustQuery("select a, b from t1")
 	res.Check(testkit.Rows("123.12345 123.1"))
+	res = tk.MustQuery("select 2.00000000000000000000000000000001 * 1.000000000000000000000000000000000000000000002")
+	res.Check(testkit.Rows("2.000000000000000000000000000000"))
 }

expression/typeinfer_test.go

@@ -591,9 +591,9 @@ func (s *testInferTypeSuite) createTestCase4MathFuncs() []typeInferTestCase {
 
 		{"round(c_int_d      )", mysql.TypeLonglong, charset.CharsetBin, mysql.BinaryFlag, 11, 0},
 		{"round(c_bigint_d   )", mysql.TypeLonglong, charset.CharsetBin, mysql.BinaryFlag, 20, 0},
-		{"round(c_float_d    )", mysql.TypeDouble, charset.CharsetBin, mysql.BinaryFlag, 12, 0},    // Should be 17.
-		{"round(c_double_d   )", mysql.TypeDouble, charset.CharsetBin, mysql.BinaryFlag, 22, 0},    // Should be 17.
-		{"round(c_decimal    )", mysql.TypeNewDecimal, charset.CharsetBin, mysql.BinaryFlag, 6, 0}, // Should be 5.
+		{"round(c_float_d    )", mysql.TypeDouble, charset.CharsetBin, mysql.BinaryFlag, 12, 0},    // flen Should be 17.
+		{"round(c_double_d   )", mysql.TypeDouble, charset.CharsetBin, mysql.BinaryFlag, 22, 0},    // flen Should be 17.
+		{"round(c_decimal    )", mysql.TypeNewDecimal, charset.CharsetBin, mysql.BinaryFlag, 6, 0}, // flen Should be 5.
 		{"round(c_datetime   )", mysql.TypeDouble, charset.CharsetBin, mysql.BinaryFlag, mysql.MaxRealWidth, 0},
 		{"round(c_time_d     )", mysql.TypeDouble, charset.CharsetBin, mysql.BinaryFlag, mysql.MaxRealWidth, 0},
 		{"round(c_timestamp_d)", mysql.TypeDouble, charset.CharsetBin, mysql.BinaryFlag, mysql.MaxRealWidth, 0},

types/mydecimal.go

@@ -713,9 +713,6 @@ func (d *MyDecimal) doMiniRightShift(shift, beg, end int) {
 // RETURN VALUE
 //  eDecOK/eDecTruncated
 func (d *MyDecimal) Round(to *MyDecimal, frac int, roundMode RoundMode) (err error) {
-	if frac > mysql.MaxDecimalScale {
-		frac = mysql.MaxDecimalScale
-	}
 	// wordsFracTo is the number of fraction words in buffer.
 	wordsFracTo := (frac + 1) / digitsPerWord
 	if frac > 0 {
@@ -1383,6 +1380,16 @@ func (d *MyDecimal) Compare(to *MyDecimal) int {
 	return 1
 }
 
+// DecimalNeg reverses decimal's sign.
+func DecimalNeg(from *MyDecimal) *MyDecimal {
+	to := *from
+	if from.IsZero() {
+		return &to
+	}
+	to.negative = !from.negative
+	return &to
+}
+
 // DecimalAdd adds two decimals, sets the result to 'to'.
 func DecimalAdd(from1, from2, to *MyDecimal) error {
 	to.resultFrac = myMaxInt8(from1.resultFrac, from2.resultFrac)
@@ -1753,7 +1760,7 @@ func DecimalMul(from1, from2, to *MyDecimal) error {
 			to.digitsFrac = int8(wordsFracTo * digitsPerWord)
 		}
 		if to.digitsInt > int8(wordsIntTo*digitsPerWord) {
-			to.digitsInt = int8(wordsFracTo * digitsPerWord)
+			to.digitsInt = int8(wordsIntTo * digitsPerWord)
 		}
 		if tmp1 > wordsIntTo {
 			tmp1 -= wordsIntTo
@@ -1762,7 +1769,7 @@ func DecimalMul(from1, from2, to *MyDecimal) error {
 			wordsFrac1 = 0
 			wordsFrac2 = 0
 		} else {
-			tmp2 -= wordsIntTo
+			tmp2 -= wordsFracTo
 			tmp1 = tmp2 >> 1
 			if wordsFrac1 <= wordsFrac2 {
 				wordsFrac1 -= tmp1
@@ -1774,9 +1781,9 @@ func DecimalMul(from1, from2, to *MyDecimal) error {
 		}
 	}
 	startTo := wordsIntTo + wordsFracTo - 1
-	start2 := wordsInt2 + wordsFrac2 - 1
-	stop1 := 0
-	stop2 := 0
+	start2 := idx2 + wordsFrac2 - 1
+	stop1 := idx1 - wordsInt1
+	stop2 := idx2 - wordsInt2
 	to.wordBuf = zeroMyDecimal.wordBuf
 
 	for idx1 += wordsFrac1 - 1; idx1 >= stop1; idx1-- {

types/mydecimal_test.go

@@ -543,6 +543,25 @@ func (s *testMyDecimalSuite) TestMaxDecimal(c *C) {
 	}
 }
 
+func (s *testMyDecimalSuite) TestNeg(c *C) {
+	type testCase struct {
+		a      string
+		result string
+		err    error
+	}
+	tests := []testCase{
+		{"-0.0000000000000000000000000000000000000000000000000017382578996420603", "0.0000000000000000000000000000000000000000000000000017382578996420603", nil},
+		{"-13890436710184412000000000000000000000000000000000000000000000000000000000000", "13890436710184412000000000000000000000000000000000000000000000000000000000000", nil},
+		{"0", "0", nil},
+	}
+	for _, tt := range tests {
+		a := NewDecFromStringForTest(tt.a)
+		negResult := DecimalNeg(a)
+		result := negResult.ToString()
+		c.Assert(string(result), Equals, tt.result)
+	}
+}
+
 func (s *testMyDecimalSuite) TestAdd(c *C) {
 	type testCase struct {
 		a      string
@@ -627,6 +646,7 @@ func (s *testMyDecimalSuite) TestMul(c *C) {
 		{"123456", "9876543210", "1219318518533760", nil},
 		{"123", "0.01", "1.23", nil},
 		{"123", "0", "0", nil},
+		{"-0.0000000000000000000000000000000000000000000000000017382578996420603", "-13890436710184412000000000000000000000000000000000000000000000000000000000000", "0.000000000000000000000000000000", ErrTruncated},
 		{"1" + strings.Repeat("0", 60), "1" + strings.Repeat("0", 60), "0", ErrOverflow},
 	}
 	for _, tt := range tests {
@@ -635,8 +655,8 @@ func (s *testMyDecimalSuite) TestMul(c *C) {
 		b.FromString([]byte(tt.b))
 		err := DecimalMul(&a, &b, &product)
 		c.Check(err, Equals, tt.err)
-		result := product.ToString()
-		c.Assert(string(result), Equals, tt.result)
+		result := product.String()
+		c.Assert(result, Equals, tt.result)
 	}
 }