Binary Marshalling Support (#49)

Adds MarshalBinary and UnmarshalBinary methods

decimal.go

@@ -19,6 +19,7 @@ package decimal
 
 import (
 	"database/sql/driver"
+	"encoding/binary"
 	"fmt"
 	"math"
 	"math/big"
@@ -597,6 +598,34 @@ func (d Decimal) MarshalJSON() ([]byte, error) {
 	return []byte(str), nil
 }
 
+// UnmarshalBinary implements the encoding.BinaryUnmarshaler interface. As a string representation
+// is already used when encoding to text, this method stores that string as []byte
+func (d *Decimal) UnmarshalBinary(data []byte) error {
+	// Extract the exponent
+	d.exp = int32(binary.BigEndian.Uint32(data[:4]))
+
+	// Extract the value
+	d.value = new(big.Int)
+	return d.value.GobDecode(data[4:])
+}
+
+// MarshalBinary implements the encoding.BinaryMarshaler interface.
+func (d Decimal) MarshalBinary() (data []byte, err error) {
+	// Write the exponent first since it's a fixed size
+	v1 := make([]byte, 4)
+	binary.BigEndian.PutUint32(v1, uint32(d.exp))
+
+	// Add the value
+	var v2 []byte
+	if v2, err = d.value.GobEncode(); err != nil {
+		return
+	}
+
+	// Return the byte array
+	data = append(v1, v2...)
+	return
+}
+
 // Scan implements the sql.Scanner interface for database deserialization.
 func (d *Decimal) Scan(value interface{}) error {
 	// first try to see if the data is stored in database as a Numeric datatype

decimal_test.go

@@ -1519,3 +1519,29 @@ func TestNullDecimal_Value(t *testing.T) {
 		t.Errorf("%v does not equal %v", a, expected)
 	}
 }
+
+func TestBinary(t *testing.T) {
+	for x, _ := range testTable {
+
+		// Create the decimal
+		d1 := NewFromFloat(x)
+
+		// Encode to binary
+		b, err := d1.MarshalBinary()
+		if err != nil {
+			t.Errorf("error marshalling %v to binary: %v", d1, err)
+		}
+
+		// Restore from binary
+		var d2 Decimal
+		err = (&d2).UnmarshalBinary(b)
+		if err != nil {
+			t.Errorf("error unmarshalling from binary: %v", err)
+		}
+
+		// The restored decimal should equal the original
+		if !d1.Equals(d2) {
+			t.Errorf("expected %v when restoring, got %v", d1, d2)
+		}
+	}
+}