Floating point values rounding

The following code is used in runtime for stake calculation:

let required_stake = Perbill::from_rational_approximation(numerator, denominator) * total_issuance;
let balance: BalanceOf<T> = required_stake.saturated_into();

required_stake is a floating point, and with usage of saturated_into is rounded to the nearest integer. While in the typesript code

new BN((issuance * numerator) / denominator)

If sent using API, the value will be rounded down. This caused the issue when transaction gets rejected because of incorrect stake value provided, eg 101516 vs 101517. With limited information about tx failure reason, such issue can cost time to find and solve. Also, it is important to display the required stake correctly rounded in UI.

The solution used is to use explicit rounding function in typescript:

const stake = (issuance * numerator) / denominator;
const stakeBN = new BN(stake.toFixed(0));

Joystream / joystream

Floating point values rounding #298