library BytesLib {
    function concat(bytes memory _preBytes, bytes memory _postBytes)
        internal
        pure
        returns (bytes memory)
    {
        bytes memory tempBytes;
        assembly {
            // Get a location of some free memory and store it in tempBytes as
            // Solidity does for memory variables.
            tempBytes := mload(0x40)

            // Store the length of the first bytes array at the beginning of
            // the memory for tempBytes.
            let length := mload(_preBytes)
            mstore(tempBytes, length)

            // Maintain a memory counter for the current write location in the
            // temp bytes array by adding the 32 bytes for the array length to
            // the starting location.
            let mc := add(tempBytes, 0x20)
            // Stop copying when the memory counter reaches the length of the
            // first bytes array.
            let end := add(mc, length)

            for {
                // Initialize a copy counter to the start of the _preBytes data,
                // 32 bytes into its memory.
                let cc := add(_preBytes, 0x20)
            } lt(mc, end) {
                // Increase both counters by 32 bytes each iteration.
                mc := add(mc, 0x20)
                cc := add(cc, 0x20)
            } {
                // Write the _preBytes data into the tempBytes memory 32 bytes
                // at a time.
                mstore(mc, mload(cc))
            }

            // Add the length of _postBytes to the current length of tempBytes
            // and store it as the new length in the first 32 bytes of the
            // tempBytes memory.
            length := mload(_postBytes)
            mstore(tempBytes, add(length, mload(tempBytes)))

            // Move the memory counter back from a multiple of 0x20 to the
            // actual end of the _preBytes data.
            mc := end
            // Stop copying when the memory counter reaches the new combined
            // length of the arrays.
            end := add(mc, length)

            for {
                let cc := add(_postBytes, 0x20)
            } lt(mc, end) {
                mc := add(mc, 0x20)
                cc := add(cc, 0x20)
            } {
                mstore(mc, mload(cc))
            }

            // Update the free-memory pointer by padding our last write location
            // to 32 bytes: add 31 bytes to the end of tempBytes to move to the
            // next 32 byte block, then round down to the nearest multiple of
            // 32. If the sum of the length of the two arrays is zero then add
            // one before rounding down to leave a blank 32 bytes (the length block with 0).
            mstore(
                0x40,
                and(
                    add(add(end, iszero(add(length, mload(_preBytes)))), 31),
                    not(31) // Round down to the nearest 32 bytes.
                )
            )
        }
        return tempBytes;
    }

    function slice(bytes memory _bytes, uint256 _start, uint256 _length)
        internal
        pure
        returns (bytes memory)
    {
        require(_bytes.length >= (_start + _length));
        bytes memory tempBytes;
        assembly {
            switch iszero(_length)
                case 0 {
                    // Get a location of some free memory and store it in tempBytes as
                    // Solidity does for memory variables.
                    tempBytes := mload(0x40)

                    // The first word of the slice result is potentially a partial
                    // word read from the original array. To read it, we calculate
                    // the length of that partial word and start copying that many
                    // bytes into the array. The first word we copy will start with
                    // data we don't care about, but the last `lengthmod` bytes will
                    // land at the beginning of the contents of the new array. When
                    // we're done copying, we overwrite the full first word with
                    // the actual length of the slice.
                    let lengthmod := and(_length, 31)

                    // The multiplication in the next line is necessary
                    // because when slicing multiples of 32 bytes (lengthmod == 0)
                    // the following copy loop was copying the origin's length
                    // and then ending prematurely not copying everything it should.
                    let mc := add(
                        add(tempBytes, lengthmod),
                        mul(0x20, iszero(lengthmod))
                    )
                    let end := add(mc, _length)

                    for {
                        // The multiplication in the next line has the same exact purpose
                        // as the one above.
                        let cc := add(
                            add(
                                add(_bytes, lengthmod),
                                mul(0x20, iszero(lengthmod))
                            ),
                            _start
                        )
                    } lt(mc, end) {
                        mc := add(mc, 0x20)
                        cc := add(cc, 0x20)
                    } {
                        mstore(mc, mload(cc))
                    }

                    mstore(tempBytes, _length)

                    //update free-memory pointer
                    //allocating the array padded to 32 bytes like the compiler does now
                    mstore(0x40, and(add(mc, 31), not(31)))
                }
                //if we want a zero-length slice let's just return a zero-length array
                default {
                    tempBytes := mload(0x40)
                    mstore(0x40, add(tempBytes, 0x20))
                }
        }

        return tempBytes;
    }

    // Pad a bytes array to 32 bytes
    function leftPad(bytes memory _bytes) internal pure returns (bytes memory) {
        // may underflow if bytes.length < 32. Hence using SafeMath.sub
        bytes memory newBytes = new bytes(SafeMath.sub(32, _bytes.length));
        return concat(newBytes, _bytes);
    }

    function toBytes32(bytes memory b) internal pure returns (bytes32) {
        require(b.length >= 32, "Bytes array should atleast be 32 bytes");
        bytes32 out;
        for (uint256 i = 0; i < 32; i++) {
            out |= bytes32(b[i] & 0xFF) >> (i * 8);
        }
        return out;
    }

    function toBytes4(bytes memory b) internal pure returns (bytes4 result) {
        assembly {
            result := mload(add(b, 32))
        }
    }

    function fromBytes32(bytes32 x) internal pure returns (bytes memory) {
        bytes memory b = new bytes(32);
        for (uint256 i = 0; i < 32; i++) {
            b[i] = bytes1(uint8(uint256(x) / (2**(8 * (31 - i)))));
        }
        return b;
    }

    function fromUint(uint256 _num) internal pure returns (bytes memory _ret) {
        _ret = new bytes(32);
        assembly {
            mstore(add(_ret, 32), _num)
        }
    }

    function toUint(bytes memory _bytes, uint256 _start)
        internal
        pure
        returns (uint256)
    {
        require(_bytes.length >= (_start + 32));
        uint256 tempUint;
        assembly {
            tempUint := mload(add(add(_bytes, 0x20), _start))
        }
        return tempUint;
    }

    function toAddress(bytes memory _bytes, uint256 _start)
        internal
        pure
        returns (address)
    {
        require(_bytes.length >= (_start + 20));
        address tempAddress;
        assembly {
            tempAddress := div(
                mload(add(add(_bytes, 0x20), _start)),
                0x1000000000000000000000000
            )
        }

        return tempAddress;
    }
}
function leftPad(bytes memory _bytes) internal pure returns (bytes memory) {
    // may underflow if bytes.length < 32. Hence using SafeMath.sub
    bytes memory newBytes = new bytes(SafeMath.sub(32, _bytes.length));
    return concat(newBytes, _bytes);
}

// Pad a bytes array to 32 bytes