Add new helper methods: BigInt, BigFloat (#171)

* Add new helper methods: BigInt, BigFloat
* Add few tests cases showing loss of precision after casting

decimal.go

@@ -695,6 +695,22 @@ func (d Decimal) IntPart() int64 {
 	return scaledD.value.Int64()
 }
 
+// BigInt returns integer component of the decimal as a BigInt.
+func (d Decimal) BigInt() *big.Int {
+	scaledD := d.rescale(0)
+	i := &big.Int{}
+	i.SetString(scaledD.String(), 10)
+	return i
+}
+
+// BigFloat returns decimal as BigFloat.
+// Be aware that casting decimal to BigFloat might cause a loss of precision.
+func (d Decimal) BigFloat() *big.Float {
+	f := &big.Float{}
+	f.SetString(d.String())
+	return f
+}
+
 // Rat returns a rational number representation of the decimal.
 func (d Decimal) Rat() *big.Rat {
 	d.ensureInitialized()

decimal_test.go

@@ -1724,6 +1724,59 @@ func TestIntPart(t *testing.T) {
 	}
 }
 
+func TestBigInt(t *testing.T) {
+	testCases := []struct {
+		Dec       string
+		BigIntRep string
+	}{
+		{"0.0", "0"},
+		{"0.00000", "0"},
+		{"0.01", "0"},
+		{"12.1", "12"},
+		{"9999.999", "9999"},
+		{"-32768.01234", "-32768"},
+		{"-572372.0000000001", "-572372"},
+	}
+
+	for _, testCase := range testCases {
+		d, err := NewFromString(testCase.Dec)
+		if err != nil {
+			t.Fatal(err)
+		}
+		if d.BigInt().String() != testCase.BigIntRep {
+			t.Errorf("expect %s, got %s", testCase.BigIntRep, d.BigInt())
+		}
+	}
+}
+
+func TestBigFloat(t *testing.T) {
+	testCases := []struct {
+		Dec         string
+		BigFloatRep string
+	}{
+		{"0.0", "0"},
+		{"0.00000", "0"},
+		{"0.01", "0.01"},
+		{"12.1", "12.1"},
+		{"9999.999", "9999.999"},
+		{"-32768.01234", "-32768.01234"},
+		{"-572372.0000000001", "-572372"},
+		{"512.012345123451234512345", "512.0123451"},
+		{"1.010101010101010101010101010101", "1.01010101"},
+		{"55555555.555555555555555555555", "55555555.56"},
+	}
+
+	for _, testCase := range testCases {
+		d, err := NewFromString(testCase.Dec)
+		if err != nil {
+			t.Fatal(err)
+		}
+		if d.BigFloat().String() != testCase.BigFloatRep {
+			t.Errorf("expect %s, got %s", testCase.BigFloatRep, d.BigFloat())
+		}
+	}
+}
+
 func TestDecimal_Min(t *testing.T) {
 	// the first element in the array is the expected answer, rest are inputs
 	testCases := [][]float64{