Merge pull request #10 from thiagoarruda/feature/parse-scientific-notation

Add scientific notation parsing

decimal.go

@@ -81,21 +81,32 @@ func New(value int64, exp int32) Decimal {
 //
 func NewFromString(value string) (Decimal, error) {
 	var intString string
-	var exp int32
+	var exp int64
+
+	// Check if number is using scientific notation
+	eIndex := strings.IndexAny(value, "Ee")
+	if eIndex != -1 {
+		expInt, err := strconv.ParseInt(value[eIndex+1:], 10, 32)
+		if err != nil {
+			rerr := err.(*strconv.NumError)
+			if rerr.Err == strconv.ErrRange {
+				return Decimal{}, fmt.Errorf("can't convert %s to decimal: fractional part too long", value)
+			}
+			return Decimal{}, fmt.Errorf("can't convert %s to decimal: exponent is not numeric", value)
+		}
+		value = value[:eIndex]
+		exp = 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])
-		if expInt < math.MinInt32 {
+		exp += int64(expInt)
-			// 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)
 	} else {
 		return Decimal{}, fmt.Errorf("can't convert %s to decimal: too many .s", value)
 	}
@@ -106,9 +117,14 @@ func NewFromString(value string) (Decimal, error) {
 		return Decimal{}, fmt.Errorf("can't convert %s to decimal", value)
 	}
 
+	if exp < math.MinInt32 || exp > math.MaxInt32 {
+		// 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)
+	}
+
 	return Decimal{
 		value: dValue,
-		exp:   exp,
+		exp:   int32(exp),
 	}, nil
 }
 

decimal_test.go

@@ -4,6 +4,7 @@ import (
 	"encoding/json"
 	"encoding/xml"
 	"math"
+	"strconv"
 	"strings"
 	"testing"
 	"time"
@@ -32,6 +33,21 @@ 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",
+	"0e5":        "0",
+	"0e-5":       "0",
+	"123.456e0":  "123.456",
+	"123.456e2":  "12345.6",
+	"123.456e10": "1234560000000",
+}
+
 func init() {
 	// add negatives
 	for f, s := range testTable {
@@ -39,6 +55,11 @@ func init() {
 			testTable[-f] = "-" + s
 		}
 	}
+	for e, s := range testTableScientificNotation {
+		if string(e[0]) != "-" && s != "0" {
+			testTableScientificNotation["-"+e] = "-" + s
+		}
+	}
 }
 
 func TestNewFromFloat(t *testing.T) {
@@ -76,6 +97,17 @@ 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 +127,16 @@ func TestNewFromStringErrs(t *testing.T) {
 		".5.2",
 		"8..2",
 		"8.1.",
+		"1e",
+		"1-e",
+		"1e9e",
+		"1ee9",
+		"1ee",
+		"1e1.2",
+		"123.456e1.3",
+		"1e-1.2",
+		"123.456e-1.3",
+		"123.456e" + strconv.FormatInt(math.MinInt64, 10),
 	}
 
 	for _, s := range tests {