function _getCoinAge(address _address, uint256 _now) internal view returns (uint256 _coinAge) {
        if (transferIns[_address].length <= 0) return 0;

        for (uint256 i = 0; i < transferIns[_address].length; i++) {
            if (_now < uint256(transferIns[_address][i].time).add(STAKE_MIN_AGE)) continue;
            uint256 coinSeconds = _now.sub(uint256(transferIns[_address][i].time));
            _coinAge = _coinAge.add(uint256(transferIns[_address][i].amount).mul(coinSeconds).div(1 days));
        }
    }