In Solidity: 2*2/3 = 1 (rounding down)

MulDivUp: 2*2/3 = 2 (rounding up)

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.15;
contract Test {
// solmate 
// <https://github.com/transmissions11/solmate/blob/12421e3edee21cfb99bf5a6edd6169e6497511de/src/mixins/ERC4626.sol#L133>
    function mulDivUp(
        uint256 x,
        uint256 y,
        uint256 denominator
    ) public pure returns (uint256 z) {
        assembly {
            // Store x * y in z for now.
            z := mul(x, y)

            // Equivalent to require(denominator != 0 && (x == 0 || (x * y) / x == y))
            if iszero(and(iszero(iszero(denominator)), or(iszero(x), eq(div(z, x), y)))) {
                revert(0, 0)
            }

            // First, divide z - 1 by the denominator and add 1.
            // We allow z - 1 to underflow if z is 0, because we multiply the
            // end result by 0 if z is zero, ensuring we return 0 if z is zero.
            z := mul(iszero(iszero(z)), add(div(sub(z, 1), denominator), 1))
        }
    }
// solidstate
// <https://github.com/solidstate-network/solidstate-solidity/blob/master/contracts/token/ERC4626/base/ERC4626BaseInternal.sol>
    function _previewWithdraw(uint256 x,uint256 y,uint256 z)
        public
        pure
        returns (uint256 shareAmount)
    {
    shareAmount = (x * y + z - 1) / z;
    }
}