算术运算会溢出是否有可能导致算术溢出？

Question

我想要一些有关以下合同功能的建议。断言或需要输入吐痰回来“ parsererror：预期''，但有标识符 断言（uint i = 0; i＆lt; _index+1; i ++）{“

我倾向于要求实施，给出安全的数学库在合同开始时已经进口。我看到了许多不同的合同，实现了一些问题，以确定正确的

方法

。整数算术

。

操作

contract FreezableToken is StandardToken {
    // freezing chains
    mapping (bytes32 => uint64) internal chains;
    // freezing amounts for each chain
    mapping (bytes32 => uint) internal freezings;
    // total freezing balance per address
    mapping (address => uint) internal freezingBalance;

    event Freezed(address indexed to, uint64 release, uint amount);
    event Released(address indexed owner, uint amount);

    /**
     * @dev Gets the balance of the specified address include freezing tokens.
     * @param _owner The address to query the the balance of.
     * @return An uint256 representing the amount owned by the passed address.
     */
    function balanceOf(address _owner) public view returns (uint256 balance) {
        return super.balanceOf(_owner) + freezingBalance[_owner];
    }

    /**
     * @dev Gets the balance of the specified address without freezing tokens.
     * @param _owner The address to query the the balance of.
     * @return An uint256 representing the amount owned by the passed address.
     */
    function actualBalanceOf(address _owner) public view returns (uint256 balance) {
        return super.balanceOf(_owner);
    }

    function freezingBalanceOf(address _owner) public view returns (uint256 balance) {
        return freezingBalance[_owner];
    }

    /**
     * @dev gets freezing count
     * @param _addr Address of freeze tokens owner.
     */
    function freezingCount(address _addr) public view returns (uint count) {
        uint64 release = chains[toKey(_addr, 0)];
        while (release != 0) {
            count++;
            release = chains[toKey(_addr, release)];
        }
    }

    /**
     * @dev gets freezing end date and freezing balance for the freezing portion specified by index.
     * @param _addr Address of freeze tokens owner.
     * @param _index Freezing portion index. It ordered by release date descending.
     */
    function getFreezing(address _addr, uint _index) public view returns (uint64 _release, uint _balance) {
        for (uint i = 0; i < _index + 1; i++) { **<- Error Here ``< _index + 1; i++)``**
            _release = chains[toKey(_addr, _release)];
            if (_release == 0) {
                return;
            }
        }
        _balance = freezings[toKey(_addr, _release)];
    }

    /**
     * @dev freeze your tokens to the specified address.
     *      Be careful, gas usage is not deterministic,
     *      and depends on how many freezes _to address already has.
     * @param _to Address to which token will be freeze.
     * @param _amount Amount of token to freeze.
     * @param _until Release date, must be in future.
     */
    function freezeTo(address _to, uint _amount, uint64 _until) public {
        require(_to != address(0));
        require(_amount <= balances[msg.sender]);

        balances[msg.sender] = balances[msg.sender].sub(_amount);

        bytes32 currentKey = toKey(_to, _until);
        freezings[currentKey] = freezings[currentKey].add(_amount);
        freezingBalance[_to] = freezingBalance[_to].add(_amount);

        freeze(_to, _until);
        emit Transfer(msg.sender, _to, _amount);
        emit Freezed(_to, _until, _amount);
    }

    /**
     * @dev release first available freezing tokens.
     */
    function releaseOnce() public {
        bytes32 headKey = toKey(msg.sender, 0);
        uint64 head = chains[headKey];
        require(head != 0);
        require(uint64(block.timestamp) > head);
        bytes32 currentKey = toKey(msg.sender, head);

        uint64 next = chains[currentKey];

        uint amount = freezings[currentKey];

        balances[msg.sender] = balances[msg.sender].add(amount);
        freezingBalance[msg.sender] = freezingBalance[msg.sender].sub(amount);

        if (next == 0) {
        } else {
            chains[headKey] = next;
        }
        emit Released(msg.sender, amount);
    }

    /**
     * @dev release all available for release freezing tokens. Gas usage is not deterministic!
     * @return how many tokens was released
     */
    function releaseAll() public returns (uint tokens) {
        uint release;
        uint balance;
        (release, balance) = getFreezing(msg.sender, 0);
        while (release != 0 && block.timestamp > release) {
            releaseOnce();
            tokens += balance;
            (release, balance) = getFreezing(msg.sender, 0);
        }
    }

    function toKey(address _addr, uint _release) internal pure returns (bytes32 result) {
        // WISH masc to increase entropy
        result = 0x5749534800000000000000000000000000000000000000000000000000000000;
        assembly {
         result := or(result, mul(_addr, 0x10000000000000000))
         result := or(result, and(_release, 0xffffffffffffffff))
        }
    }

    function freeze(address _to, uint64 _until) internal {
        require (_until > block.timestamp);
        bytes32 key = toKey(_to, _until);
        bytes32 parentKey = toKey(_to, uint64(0));
        uint64 next = chains[parentKey];

        if (next == 0) {
            chains[parentKey] = _until;
            return;
        }

        bytes32 nextKey = toKey(_to, next);
        uint parent;

        while (next != 0 && _until > next) {
            parent = next;
            parentKey = nextKey;

            next = chains[nextKey];
            nextKey = toKey(_to, next);
        }

        if (_until == next) {
            return;
        }

        if (next != 0) {
            chains[key] = next;
        }

        chains[parentKey] = _until;
    }
}```


  [1]: https://i.sstatic.net/ayg2D.png

Answer 1

基于上下文，我假设错误消息“算术操作会溢出”。来自静态分析工具。

假设您使用的固体版本低于0.8.0，则for循环定义在理论上很容易受到整数溢出的影响。但是，只有当_index为2^256时，uint的最大值。此值将使_index + 1表达式溢出。

仅导入Safemath库是不够的。您还需要使用其功能而不是本机算术操作来防止溢出。

contract FreezableToken is StandardToken {
    // allows to use functions of the library on `uint` type
    using SafeMath for uint;

    function getFreezing() public {
        // use the `add()` function of the library instead of the `+` operation
        for (uint i = 0; i < _index.add(1); i = i.add(1)) {

或升级到Solidity版本0.8+，该版本在语言级别上检查溢出，因此您不必使用Safemath库。