Checklist

• I have searched the existing issues and pull requests for duplicates.

Type of Issue

• New vulnerability addition
• Feature request
• Update existing vulnerability

Description

Division before multiplication

Solidity's integer division truncates. Thus, performing division before multiplication can lead to precision loss.

contract A {
	function func(uint n) public {
        coins = (oldSupply / n) * interest; // causes precision loss
    }
}

If n is greater than oldSupply, coins will be zero. Also, the fractional part is truncated due to integer division in solidity.

1 / 3 = 0 // rounding to 0
3 / 2 = 1 // 0.5 is truncated

Let's expand further,
When oldSupply = 5; n = 10, interest = 2,
if (oldSupply / n) * interest is used, coins value will round to zero.
and If (oldSupply * interest / n) is used, coins value will be 1.

Similarly for larger values,
When oldSupply = 119, n = 10, interest = 10,
if (oldSupply / n) * interest is used, coins value will be 110
and if (oldSupply * interest / n) is used, coins value will be 119.

Here, 9 coins were lost due to division before multiplication but following multiplication before division gave the exact value of coins. Thus, multiplication before division can prevent loss of precision due to truncation.