Solidity-Contracts-Full-Tutorials-A-Z/44MostSignificantBitFunction.sol at master · BlockChain-Creativity/Solidity-Contracts-Full-Tutorials-A-Z · GitHub

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/*

# Bitwise Operators
Most significant bit in assembly

*/

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.17;

contract MostSignificantBitAssembly {
    function mostSignificantBit(uint x) external pure returns (uint msb) {
        assembly {
            let f := shl(7, gt(x, 0xFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF))
            x := shr(f, x)
            // or can be replaced with add
            msb := or(msb, f)
        }
        assembly {
            let f := shl(6, gt(x, 0xFFFFFFFFFFFFFFFF))
            x := shr(f, x)
            msb := or(msb, f)
        }
        assembly {
            let f := shl(5, gt(x, 0xFFFFFFFF))
            x := shr(f, x)
            msb := or(msb, f)
        }
        assembly {
            let f := shl(4, gt(x, 0xFFFF))
            x := shr(f, x)
            msb := or(msb, f)
        }
        assembly {
            let f := shl(3, gt(x, 0xFF))
            x := shr(f, x)
            msb := or(msb, f)
        }
        assembly {
            let f := shl(2, gt(x, 0xF))
            x := shr(f, x)
            msb := or(msb, f)
        }
        assembly {
            let f := shl(1, gt(x, 0x3))
            x := shr(f, x)
            msb := or(msb, f)
        }
        assembly {
            let f := gt(x, 0x1)
            msb := or(msb, f)
        }
    }
}