Merge pull request #7 from stasundr/wei_converter

Wei converter with overflow checks

decimal.go

@@ -244,6 +244,34 @@ func (d *Decimal) FromString(value string) bool {
 	return true
 }
 
+func (d *Decimal) RescaleOverflow(mantissa uint8) (value *Decimal, overflow bool) {
+	if d == nil {
+		return nil, false
+	}
+
+	if mantissa == d.mantissa {
+		return d, false
+	}
+
+	if mantissa > d.mantissa {
+		_, isOverflow := d.value.MulOverflow(d.value, ExpScale(int16(mantissa-d.mantissa)))
+		if isOverflow {
+			return nil, isOverflow
+		}
+
+		d.mantissa = mantissa
+		return d, false
+	}
+
+	if mantissa < d.mantissa {
+		d.value.Div(d.value, ExpScale(int16(d.mantissa-mantissa)))
+		d.mantissa = mantissa
+		return d, false
+	}
+
+	return d, false
+}
+
 func (d *Decimal) Rescale(mantissa uint8) *Decimal {
 	if d == nil {
 		return nil

wei.go

@@ -11,3 +11,16 @@ func ConvertToWei(dec *Decimal, mantissa uint8) *big.Int {
 
 	return NewDecimal(dec).Rescale(mantissa).ToBig()
 }
+
+func ConvertToWeiOverflow(dec *Decimal, mantissa uint8) (wei *big.Int, overflow bool) {
+	if dec == nil || dec.value == nil {
+		return new(big.Int).SetUint64(0), false
+	}
+
+	value, isOverflow := NewDecimal(dec).RescaleOverflow(mantissa)
+	if isOverflow {
+		return nil, isOverflow
+	}
+
+	return value.ToBig(), false
+}

wei_test.go

@@ -56,4 +56,24 @@ func TestConvertToWei(t *testing.T) {
 	expected, ok = new(big.Int).SetString("ffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff", 16)
 	assert.True(t, ok)
 	assert.Equal(t, expected, ConvertToWei(actual, 18))
+
+	actual, ok = NewDecimalFromString("115792089237316195423570985008687907853269984665640564039457584007913129639935")
+	assert.True(t, ok)
+	expected, ok = new(big.Int).SetString("ffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff", 16)
+	assert.True(t, ok)
+	actualWei, overflow := ConvertToWeiOverflow(actual, 18)
+	assert.True(t, overflow)
+	assert.Nil(t, actualWei)
+
+	actual, ok = NewDecimalFromString("115792089237316195423570985008687907853269984665640564039457.584007913129639936")
+	assert.False(t, ok)
+	assert.Nil(t, actual)
+
+	actual, ok = NewDecimalFromString("115792089237316195423570985008687907853269984665640564039457.584007913129639935")
+	assert.True(t, ok)
+	expected, ok = new(big.Int).SetString("ffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff", 16)
+	assert.True(t, ok)
+	actualWei, overflow = ConvertToWeiOverflow(actual, 18)
+	assert.False(t, overflow)
+	assert.Equal(t, expected, actualWei)
 }