Add scientific notation parsing

decimal.go

@@ -82,12 +82,23 @@ func New(value int64, exp int32) Decimal {
 func NewFromString(value string) (Decimal, error) {
 	var intString string
 	var exp int32
+
+	// Check if number is using scientific notation
+	eIndex := strings.IndexAny(value, "Ee")
+	if eIndex != -1 {
+		expInt, err := strconv.ParseInt(value[eIndex+1:len(value)], 10, 32)
+		if err != nil {
+			return Decimal{}, fmt.Errorf("can't convert %s to decimal: exponent is not numeric", value)
+		}
+		value = value[0:eIndex]
+		exp = int32(expInt)
+	}
+
 	parts := strings.Split(value, ".")
 	if len(parts) == 1 {
 		// There is no decimal point, we can just parse the original string as
 		// an int
 		intString = value
-		exp = 0
 	} else if len(parts) == 2 {
 		intString = parts[0] + parts[1]
 		expInt := -len(parts[1])
@@ -95,7 +106,7 @@ func NewFromString(value string) (Decimal, error) {
 			// NOTE(vadim): I doubt a string could realistically be this long
 			return Decimal{}, fmt.Errorf("can't convert %s to decimal: fractional part too long", value)
 		}
-		exp = int32(expInt)
+		exp += int32(expInt)
 	} else {
 		return Decimal{}, fmt.Errorf("can't convert %s to decimal: too many .s", value)
 	}

decimal_test.go

@@ -32,6 +32,16 @@ var testTable = map[float64]string{
 	.1000000000000008:   "0.1000000000000008",
 }
 
+var testTableScientificNotation = map[string]string{
+	"1e9":       "1000000000",
+	"2.41E-3":   "0.00241",
+	"24.2E-4":   "0.00242",
+	"243E-5":    "0.00243",
+	"-1e-5":     "-0.00001",
+	"-245E3":    "-245000",
+	"1.2345E-1": "0.12345",
+}
+
 func init() {
 	// add negatives
 	for f, s := range testTable {
@@ -76,6 +86,17 @@ func TestNewFromString(t *testing.T) {
 				d.value.String(), d.exp)
 		}
 	}
+
+	for e, s := range testTableScientificNotation {
+		d, err := NewFromString(e)
+		if err != nil {
+			t.Errorf("error while parsing %s", e)
+		} else if d.String() != s {
+			t.Errorf("expected %s, got %s (%s, %d)",
+				s, d.String(),
+				d.value.String(), d.exp)
+		}
+	}
 }
 
 func TestNewFromStringErrs(t *testing.T) {
@@ -95,6 +116,9 @@ func TestNewFromStringErrs(t *testing.T) {
 		".5.2",
 		"8..2",
 		"8.1.",
+		"1e",
+		"1-e",
+		"1e9e",
 	}
 
 	for _, s := range tests {