gistfile1.sol

/*
    Simple vesting contract. amount of tokens `owner` can withdraw is
    linear to how far they are in the vesting schedule.
    E.g. if `period` is 4 years then after 2 years 50% can be withdrawn.
    
    The vesting is continous, allowing `owner` to withdraw at any time.
*/

pragma solidity ^0.4.2;

contract Vested {
    address owner;
    uint original_amount;
    uint created;
    uint cliff;
    uint fully_vested;
    function Vested(address _owner, uint period, uint _cliff) payable {
        owner           = _owner;
        original_amount = msg.value;
        created         = now;
        cliff           = _cliff;
        fully_vested    = now + period;
    }
    
    function withdraw(uint amount) {
        if (msg.sender != owner)     { throw; }
        if (now < (created + cliff)) { throw; }
        
        uint allowed;
        if (now >= fully_vested) {
            allowed = this.balance;
        } else {
            // improve precision by mul with constant factor before div
            uint mul = ((fully_vested - created) * 1000) / (now - created);
            uint vested = (original_amount * mul) / 1000;
            allowed = vested - (original_amount - this.balance);
        }
        if (amount > allowed)    { throw; }
        
        if (!owner.send(amount)) { throw; }
    }
}