Summary

In Solidity division can result in rounding down errors, hence to minimize any rounding errors we always want to perform multiplication before division.

Vulnerability Details

In above code we can see the priceEurUsd will divides afterwards it will multiplied by _hundredPC this will make less precision than expected.

Take a scenario :-

price = 8965

rate = 20

Output

DivBefore = 1780

multiplyBef = 1793

We can observe multiplyBef gives accurate output but DivBefore gives -13. Solidity doesn't support floating points.

Impact

By doing the division before multiplication leads to rounding issues.

Tools Used

Manual View

Recommendations

We can make division after multiplication which can mitigate rounding related issues as much as possible. The computations can be much more complex and forming them into a multiplication first formula can be challenging at times