Memory Operations Demo

contract MemoryOperationsDemo {
    function normalSumOfArray(uint[] arr) public view returns (uint sum) {
        for (uint i = 0; i < arr.length; i++) {
            sum = arr[i] + sum;
        }
    }

    function asmSumOfArray(uint[] arr) public view returns (uint sum) {
        assembly {
            let len := mload(arr)
            let elAddress := add(arr, 0x20)
            let i := 0

            loop:
                sum := add(sum, mload(elAddress))
                elAddress := add(elAddress, 0x20)

                i := add(i, 1)
                jumpi(loop, lt(i, len))
        }
    }

    function normalScaleArray(uint[] arr) public view returns (uint[] result) {
        for (uint i = 0; i < arr.length; i++) {
            arr[i] = arr[i] * 2;
        }

        return arr;
    }

    function asmScaleArray(uint[] arr) public view returns (uint[] result) {
        assembly {
            let len := mload(arr)
            let elAddress := add(arr, 0x20)
            let i := 0
            let element := 0

            let offset := add(msize, 1)
            mstore(offset, 0x20) // store the data type in mem[0]. 0x20 means one-dimensional dynamic array
            mstore(add(offset, 0x20), len) // store the length in mem[1]

            loop:
                element := mload(elAddress)
                element := mul(element, 2)

                // store element i in mem[2 + i]
                mstore(add(add(offset, 0x40), mul(i, 0x20)), element)

                elAddress := add(elAddress, 0x20)

                i := add(i, 1)
                jumpi(loop, lt(i, len))

            // return mem[0..len+2]
            return(offset, add(add(offset, 0x40), mul(len, 0x20)))
        }
    }
}