presto-spi/src/main/java/io/prestosql/spi/type/Decimals.java/Decimals/rescale
class Decimals:    public static BigInteger rescale(BigInteger value, int fromScale, int toScale)
    {
        if (toScale < fromScale) {
            throw new IllegalArgumentException("target scale must be larger than source scale");
        }
        return value.multiply(bigIntegerTenToNth(toScale - fromScale));
    }