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Division before multiplication

Configuration

  • detector id: div-before-mul
  • severity: medium

Description

Find division before multiplication like 3 / 2 * 6 == 6, which has a different result compared with 3 * 6 / 2 == 9. This can result in precision loss.

It is suggested to conduct multiplication before division.

Sample code

Below shows an example. The formula farm.amount / (farm.end_date - farm.start_date) as u128 will be floored and can result in precision loss.

// https://github.com/linear-protocol/LiNEAR/blob/fdbacc68c98205cba9f42c130d464ab3114257b6/contracts/linear/src/farm.rs#L125
let reward_per_session =
    farm.amount / (farm.end_date - farm.start_date) as u128 * SESSION_INTERVAL as u128;

It's recommended to use division after multiplication to mitigate precision loss:

let reward_per_session =
    farm.amount * SESSION_INTERVAL as u128 / (farm.end_date - farm.start_date) as u128;