Loss of Precision in Conversions

[nicolasmattar]

Case:

I have a defined a new currency (BTC with 8 digits precision) and a new Exchange Provider for the Currency.

When I try to convert 1 BTC to USD, even when the exchange rate is 5489.11, the result is 5500.

Expected Result:

The conversion should return 5489.11 USD as the value 1 BTC

Possible Solution:

Maybe I am configuring something wrong, but I think the 'roundFactor' method should use the "precision" and not the "scale" to build the MathContext. (https://docs.oracle.com/javase/8/docs/api/java/math/MathContext.html)
I think this is because the library it's using the scale and MatthContext expect the Precision.

If you use scale (in this case its 2), the factor is rounded to 5.5+e3 and that is generating the wrong value.

jsr354-ri/moneta-core/src/main/java/org/javamoney/moneta/spi/AbstractCurrencyConversion.java

Line 138 in cf8ff2b

protected NumberValue roundFactor(MonetaryAmount amount, NumberValue factor) {

Thanks.