fix: large floating point wei conversion (#32)

* Fix invalid conversion on decimal numbers

* Fix floating unit point wei conversion

* Improve error

util/convert.go

@@ -6,6 +6,7 @@ package util
 import (
 	"bytes"
 	"errors"
+	"fmt"
 	"math/big"
 	"strings"
 )
@@ -21,20 +22,21 @@ func Str2BigInt(small string) (*big.Int, error) {
 }
 
 func Large2SmallUnitConverter(large string, decimal uint) (*big.Int, error) {
-	curFloat, ok := zero().SetString(large)
+	a := strings.Split(large, ".")
+	for i := 0; i < int(decimal); i++ {
+		if len(a) > 1 && len(a[1]) > i {
+			a[0] += string(a[1][i])
+		} else {
+			a[0] += "0"
+		}
+	}
+
+	b, ok := new(big.Int).SetString(a[0], 10)
 	if !ok {
-		return big.NewInt(0), errors.New("failed to convert on the given decimal")
+		return nil, fmt.Errorf("failed to convert string to big int")
 	}
-	exp, _ := zero().SetString("1" + strings.Repeat("0", int(decimal)) + ".0")
-	weiFloat := zero().Mul(curFloat, exp)
-	weiInt, _ := weiFloat.Int(nil)
-	return weiInt, nil
-}
 
-func zero() *big.Float {
-	r := big.NewFloat(0.0)
-	r.SetPrec(512)
-	return r
+	return b, nil
 }
 
 func PaddingZero(data []byte, length int) []byte {

util/convert_test.go

@@ -4,8 +4,6 @@
 package util_test
 
 import (
-	"errors"
-
 	"github.com/ChainSafe/sygma-fee-oracle/util"
 
 	"math/big"
@@ -97,20 +95,41 @@ func TestLarge2SmallUnitConverter(t *testing.T) {
 		output:    big.NewInt(1000000000),
 		outputErr: nil,
 	})
-	testcases = append(testcases, large2SmallUnitConverterTest{
-		name:      "invalid string as input",
-		input1:    "1a2b3c",
-		input2:    9,
-		output:    big.NewInt(0),
-		outputErr: errors.New("failed to convert on the given decimal"),
-	})
 	testcases = append(testcases, large2SmallUnitConverterTest{
 		name:      "valid string as input 4",
 		input1:    "100",
 		input2:    0,
 		output:    big.NewInt(100),
 		outputErr: nil,
 	})
+	testcases = append(testcases, large2SmallUnitConverterTest{
+		name:      "short decimal number",
+		input1:    "0.12",
+		input2:    18,
+		output:    big.NewInt(120000000000000000),
+		outputErr: nil,
+	})
+	testcases = append(testcases, large2SmallUnitConverterTest{
+		name:      "long decimal number",
+		input1:    "0.00000012512521",
+		input2:    18,
+		output:    big.NewInt(125125210000),
+		outputErr: nil,
+	})
+	testcases = append(testcases, large2SmallUnitConverterTest{
+		name:      "large exponent",
+		input1:    "0.000000000000000012512521",
+		input2:    32,
+		output:    big.NewInt(1251252100000000),
+		outputErr: nil,
+	})
+	testcases = append(testcases, large2SmallUnitConverterTest{
+		name:      "huge exponent",
+		input1:    "0.0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000012512521",
+		input2:    128,
+		output:    big.NewInt(125125210000000000),
+		outputErr: nil,
+	})
 
 	for _, testcase := range testcases {
 		re, err := util.Large2SmallUnitConverter(testcase.input1, testcase.input2)