expression: fix the truncate function when the first arg is 0 and s…

…econd value is too large (pingcap#58191)

close pingcap#57651

pkg/expression/builtin_math_test.go

@@ -514,6 +514,17 @@ func TestTruncate(t *testing.T) {
 		{[]any{uint64(9223372036854775808), -10}, 9223372030000000000},
 		{[]any{9223372036854775807, -7}, 9223372036850000000},
 		{[]any{uint64(18446744073709551615), -10}, uint64(18446744070000000000)},
+
+		// For issue 57651
+		{[]any{math.NaN(), 400}, math.NaN()},
+		{[]any{math.NaN(), -400}, math.NaN()},
+		{[]any{math.NaN(), 3}, math.NaN()},
+		{[]any{1.1, 400}, 1.1},
+		{[]any{1.1, -400}, 0},
+		{[]any{1.1, 3}, 1.1},
+		{[]any{0, 400}, 0},
+		{[]any{0, -400}, 0},
+		{[]any{0, 3}, 0},
 	}
 
 	Dtbl := tblToDtbl(tbl)

pkg/expression/builtin_math_vec_test.go

@@ -134,6 +134,9 @@ var vecBuiltinMathCases = map[string][]vecExprBenchCase{
 			types.NewFieldTypeBuilder().SetType(mysql.TypeInt24).SetFlag(mysql.UnsignedFlag).BuildP(),
 		}, geners: []dataGenerator{nil, newRangeInt64Gener(-10, 10)}},
 		{retEvalType: types.ETDecimal, childrenTypes: []types.EvalType{types.ETDecimal, types.ETInt}},
+
+		// For issue 57651
+		{retEvalType: types.ETReal, childrenTypes: []types.EvalType{types.ETReal, types.ETInt}, geners: []dataGenerator{newSelectRealGener([]float64{0, -0.1, 0.1, -1.1, 1.1}), newRangeInt64Gener(-1000, 1000)}},
 	},
 	ast.Rand: {
 		{retEvalType: types.ETReal, childrenTypes: []types.EvalType{types.ETInt}, geners: []dataGenerator{newDefaultGener(0, types.ETInt)}},

pkg/types/helper.go

@@ -55,7 +55,10 @@ func Round(f float64, dec int) float64 {
 func Truncate(f float64, dec int) float64 {
 	shift := math.Pow10(dec)
 	tmp := f * shift
-	if math.IsInf(tmp, 0) {
+
+	// When dec is larger than 308, the shift will be inf.
+	// At the same time, if f is 0, tmp will be NaN.
+	if math.IsInf(tmp, 0) || math.IsNaN(tmp) {
 		return f
 	}
 	if shift == 0.0 {