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I'm trying to compose a formula in Solidity that has a combination of unsigned integers, signed and exponents, however having a hard time figuring out how to do so.

The formula would look something like f(x)=15-2^(-0.1x+3.5) where 15, -0.1 and 3.5 are constants, and x is a uint256 with an ERC20 Token Balance (with 18 decimals).

The function signature has to be something like function calculate(uint256 price) public view returns (uint256)

I've looked at using OpenZeppelin SafeCast, ABDKMath64x64 and other libraries, but whatever I've tried has failed.

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Basically if you check that price is smaller than max_int256, you can cast it into a signed number and work from there.

Your token is probably using some precision, i.e. has decimal set to 18, so price received is an int that represents a 18 precision real number.

All you have to do is convert your numbers to the same precision level (multiply by 1e18) and do the rest as usual.

    uint256 constant DECIMALS = 18;

    function calculate(uint256 _price) public pure returns (uint256) {
        require(_price < 0x8FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF, "input too big");
        int256 price = int256(_price);
        int256 power = 1e18*0.1 * price + 1e18*3.5;
        int256 y = 15 - 2 ^ power;
        return uint256(y);
    }

Make sure you use solidity ^0.8.0 or alternatively use SafeMath library to avoid arithmetic overflow issues.

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  • I was under the impression exponentiation is done using ** rather than ^ and can only be done using uint256. I've tried following your code by doing this instead: uint256 y = 15 - 2 ** uint256(power); but that "Transaction reverted without a reason string". The input I'm trying is 1e18
    – teh0wner
    May 4, 2022 at 15:01

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