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I'm kinda struggling here to find a solution.

I have a code where user can deposit token like USDC, DAI etc...

For example USDC had 6 decimals and DAI has 18 decimals.

How can I have a generic fee calculation in my function so it handle all different case when decimals are differents and also avoid rounding by 0 ?

I have something like this for the calculation :

uint256 feeToCollect = (amount * feeBps * 10**18) / BPS; 

uint256 amountWithFee = amount + fee; 

IERC20(token).transferFrom(msg.sender, address(this), amountWithFee;

amount = amount that the user deposit

feeBps = 10 so it's 0.1%

BPS = 10000

10**18 is a scale to avoid rounding by 0.

Thank you for your help !

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  • Don't hardcode the decimal value, get it dynamically from IERC20(token).decimals(); Feb 29 at 16:48
  • Correct thanks but I have the following issue when I increment the deposited amount and the fees : Let say I deposit 100 tokens and have 2 mapping that keep track of the deposit and fees : mapping(address => uint256) public totalDeposited; mapping(address => uint256) public feeCollected; uint256 feeToCollect = (amount * feeBps * 10**18) / BPS; uint256 amountWithFee = amount + fee; IERC20(token).transferFrom(msg.sender, address(this), amountWithFee; totalDeposited += amount; feeCollected += fee; Mappings return : 100 -> totalDeposit 100000000000000000 -> feeCollected
    – 0xAurora
    Feb 29 at 22:15

1 Answer 1

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If I understand the math problem correctly, the code should look something like that:

uint decimalFactor = IERC20(token).decimals(); //should return 18 or 6 in your case.

uint256 feeToCollect = (amount * feeBps * 10**decimalFactor) / BPS;

2
  • Correct thanks but I have the following issue when I increment the deposited amount and the fees : Let say I deposit 100 tokens and have 2 mapping that keep track of the deposit and fees : mapping(address => uint256) public totalDeposited; mapping(address => uint256) public feeCollected; uint256 feeToCollect = (amount * feeBps * 10**18) / BPS; uint256 amountWithFee = amount + fee; IERC20(token).transferFrom(msg.sender, address(this), amountWithFee; totalDeposited += amount; feeCollected += fee; Mappings return : 100 -> totalDeposit 100000000000000000 -> feeCollected
    – 0xAurora
    Feb 29 at 22:20
  • Add explanation for readers on how calculation works.
    – DevCrypto
    Mar 5 at 12:20

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