    function _borrowLimit(
        address _bathToken,
        address _asset,
        uint256 _assetAmount,
        uint256 _leverage
    ) internal returns (uint256 _limit, uint256 _lastBorrow) {
        (, uint256 _collateralFactor, ) = comptroller.markets(_bathToken);
        // how much is needed to borrow in asset form
        uint256 _desiredAmount = wmul(_assetAmount, _leverage);


        // check if collateral was already supplied
        uint256 _minted = IERC20(_bathToken).balanceOf(address(this));
	// how much is borrowed on a current loop
        uint256 _loopBorrowed;


        while (_assetAmount <= _desiredAmount) {
            if (_limit == 0) {
		// if collateral already provided
                if (_minted != 0) {
                    uint256 _max = _maxBorrow(_bathToken);


		    // take into account previous collateral
                    _loopBorrowed = wmul(_assetAmount, _collateralFactor).add(
                        _max
                    );
                } else {
                    _loopBorrowed = wmul(_assetAmount, _collateralFactor);
                }
            } else {
                _loopBorrowed = wmul(_loopBorrowed, _collateralFactor);
            }


            // here _assetAmount refers to the
            // TOTAL asset amount in the position
            _assetAmount += _loopBorrowed;


            if (_assetAmount > _desiredAmount) {
                // in case we've borrowed more than needed
                // return excess and calculate how much is
                // needed to borrow on the last loop
                // to not overflow _desiredAmount
                uint256 _borrowDelta = _desiredAmount.sub(
                    _assetAmount.sub(_loopBorrowed)
                );
                _lastBorrow = _borrowDelta.mul(WAD).div(_loopBorrowed);


                _limit++;
                break;
            } else if (_assetAmount == _desiredAmount) {
                // 1x short or perfect matching
                _limit++;
                break;
            } else {
                // default case
                _limit++;
            }
        }
    }
