core: vm: sqlvm: types: fix encode bug when exponent is negative (#270)

It is possible that the number to encode is produced by arithmetic
operations and has negative exponent even when it is an integer.
Properly handle this case and modify test cases to check it.

2 files changed, 10 insertions, 4 deletions

diff --git a/core/vm/sqlvm/ast/types.go b/core/vm/sqlvm/ast/types.go
index 1928d2338..c006086e9 100644
--- a/core/vm/sqlvm/ast/types.go
+++ b/core/vm/sqlvm/ast/types.go
@@ -163,8 +163,14 @@ func decimalEncode(size int, d decimal.Decimal) []byte {
 		return ret
 	}
 
-	exp := new(big.Int).Exp(bigIntTen, big.NewInt(int64(d.Exponent())), nil)
-	b := new(big.Int).Mul(d.Coefficient(), exp)
+	var b *big.Int
+	if exponent := int64(d.Exponent()); exponent >= 0 {
+		exp := new(big.Int).Exp(bigIntTen, big.NewInt(exponent), nil)
+		b = new(big.Int).Mul(d.Coefficient(), exp)
+	} else {
+		exp := new(big.Int).Exp(bigIntTen, big.NewInt(-exponent), nil)
+		b = new(big.Int).Div(d.Coefficient(), exp)
+	}
 
 	if s > 0 {
 		bs := b.Bytes()
diff --git a/core/vm/sqlvm/ast/types_test.go b/core/vm/sqlvm/ast/types_test.go
index 17378d2bd..fe125ba2a 100644
--- a/core/vm/sqlvm/ast/types_test.go
+++ b/core/vm/sqlvm/ast/types_test.go
@@ -93,9 +93,9 @@ func (s *TypesTestSuite) TestDecodeError() {
 }
 
 func (s *TypesTestSuite) TestEncodeAndDecodeDecimal() {
-	pos := decimal.New(15, 0)
+	pos := decimal.New(15, 1)
 	zero := decimal.Zero
-	neg := decimal.New(-15, 0)
+	neg := decimal.New(-150, -1)
 
 	s.requireEncodeAndDecodeDecimalNoError(
 		ComposeDataType(DataTypeMajorInt, 2),