I want to implement 4.pow(0.5)

[GalaxySciTech]

Can you help me, I want to implement 4.pow(0.5)
This calculation
What should I do

[PaulRBerg]

Hey @lailaibtc! You can do that calculation like this:

// SPDX-License-Identifier: Unlicense
pragma solidity >=0.8.4;

import "prb-math/contracts/PRBMathUD60x18.sol";

contract UnsignedConsumer {
    using PRBMathUD60x18 for uint256;

    function foo() external returns (uint256 result) {
        const base = 4e18;
        const exp = 5e17;
        result = base.pow(exp);
    } 
}

You can try this on Remix. The result you get be should be 2000000000000000000, which is 2e18.

Make sure to read the NatSpec documentation for the pow function so that you understand how it works more precisely. Also check out this convertor tool that will help you convert between 18-decimals number (wads) and normal numbers.

[PaulRBerg]

Update: Actually, to use a sub-unitary base like 0.5, you have to switch to using the signed flavour of the library PRBMathSD59x18. I shall refer you to the README again, but also to this forum post that explains how the log2 function works, among other things:

https://www.smartcontractresearch.org/t/deep-diving-into-prbmath-a-library-for-advanced-fixed-point-math/686

[GalaxySciTech]

hello,If I use this way, will there be any safety hazards? If so, how do I solve it?

using PRBMathSD59x18 for int256;

    function pow(uint256 x, uint256 y) internal view returns (uint256) {
        return uint256(int256(x).pow(int256(y)));
 }

[PaulRBerg]

There is one issue with that code, yes. You have to check that the uint256 values fit within int256, like I am doing here.

[GalaxySciTech]

thank u very much,i get it

[PaulRBerg]

No worries