Sweet sweet overflow checking in Yul (almost assembly)

fmulfdiv

// SPDX-License-Identifier: GPL-3.0

pragma solidity >=0.7.0 <0.9.0;

contract Test {
    function fmul(
       uint256 x,
       uint256 y,
       uint256 baseUnit
    ) public pure returns (uint256 z) {
        assembly {
            let a := mul(x, y) // 
            switch eq(div(a, x), y) // multiplication overflow check
                case 1 { z := div(a, baseUnit) }
                case 0 { revert(0, 0) }
        }
    }
    
    function fdiv(
        uint256 x,
        uint256 y,
        uint256 baseUnit
    ) public pure returns (uint256 z) {
        assembly {
            let a := mul(x, baseUnit) 
            switch eq(div(a, x), baseUnit) // multiplication overflow check
                case 1 { z := div(a, y) }
                case 0 { revert(0, 0) }
        }
    }
    
    
    // Primative tests - call through remix
    
    function testFmulThrowsOnOverflow() public pure {
        uint256 x = type(uint256).max;
        uint256 y = 2; // needs to be > 1
        uint256 baseUnit = 10;
        
        fmul(x, y, baseUnit);
        
        revert("fmul() did not throw");
    }
    
    function testFmulHappyPath() public pure returns(uint256 result) {
        uint256 x = 5;
        uint256 y = 2; // needs to be > 1
        uint256 baseUnit = 10;
        
        result = fmul(x, y, baseUnit);
        
        require(result == 1, "Unexpected result from fmul()!");
    }
    
    function testFdivThrowsOnOverflow() public pure {
        uint256 x = type(uint256).max;
        uint256 y = 10; 
        uint256 baseUnit = 2; // needs to be > 1
        
        fdiv(x, y, baseUnit);
        
        revert("fmul() did not throw");
    }
    
    function testFdivHappyPath() public pure returns(uint256 result) {
        uint256 x = 5;
        uint256 y = 10; 
        uint256 baseUnit = 2; // needs to be > 1
        
        result = fdiv(x, y, baseUnit);
        
        require(result == 1, "Unexpected result from fmul()!");
    }
}