function tradeCore(uint amount, Order memory o) private constant returns(Trade t) {
        var m = matches[o.matchId];

        if (block.timestamp >= o.expiry) {
            t.status = Status.ORDER_EXPIRED;
            return;
        }

        if (m.finalized) {
            t.status = Status.MATCH_FINALIZED;
            return;
        }

        if (msg.sender == o.addr) {
            t.status = Status.SELF_TRADE;
            return;
        }

        if (amount > MAX_SANE_AMOUNT) {
            t.status = Status.AMOUNT_MALFORMED;
            return;
        }

        t.status = Status.OK;


        uint longAmount;
        uint shortAmount;

        if (o.direction == 0) {
            
            t.longAddr = msg.sender;
            longAmount = amount;

            t.shortAddr = o.addr;
            shortAmount = safeSub(o.amount, filledAmounts[o.orderHash]);
        } else {
            
            t.longAddr = o.addr;
            longAmount = safeSub(o.amount, filledAmounts[o.orderHash]);

            t.shortAddr = msg.sender;
            shortAmount = amount;
        }

        int oldLongPosition = m.positions[t.longAddr];
        int oldShortPosition = m.positions[t.shortAddr];

        longAmount = minu256(longAmount, computeEffectiveBalance(balances[t.longAddr], oldLongPosition, o.price, true));
        shortAmount = minu256(shortAmount, computeEffectiveBalance(balances[t.shortAddr], oldShortPosition, o.price, false));

        (longAmount, shortAmount) = computePriceWeightedAmounts(longAmount, shortAmount, o.price);

        if (longAmount == 0 || shortAmount == 0) {
            t.status = Status.ZERO_VALUE_TRADE;
            return;
        }


        int newLongPosition = oldLongPosition + (int(longAmount) + int(shortAmount));
        int newShortPosition = oldShortPosition - (int(longAmount) + int(shortAmount));


        t.longBalanceDelta = 0;
        t.shortBalanceDelta = 0;

        if (oldLongPosition < 0) t.longBalanceDelta += priceDivide(-oldLongPosition + min256(0, newLongPosition), 100 - o.price);
        if (newLongPosition > 0) t.longBalanceDelta -= priceDivide(newLongPosition - max256(0, oldLongPosition), o.price);

        if (oldShortPosition > 0) t.shortBalanceDelta += priceDivide(oldShortPosition - max256(0, newShortPosition), o.price);
        if (newShortPosition < 0) t.shortBalanceDelta -= priceDivide(-newShortPosition + min256(0, oldShortPosition), 100 - o.price);

        int exposureDelta = computeExposureDelta(t.longBalanceDelta, t.shortBalanceDelta, oldLongPosition, newLongPosition, oldShortPosition, newShortPosition);

        if (exposureDelta != 0) {
            if (exposureDelta == 1) {
                newLongPosition--;
                newShortPosition++;
            } else if (exposureDelta == -1) {
                t.longBalanceDelta++; 
            } else {
                assert(false);
            }

            exposureDelta = computeExposureDelta(t.longBalanceDelta, t.shortBalanceDelta, oldLongPosition, newLongPosition, oldShortPosition, newShortPosition);
            assert(exposureDelta == 0);
        }


        t.newLongPosition = newLongPosition;
        t.newShortPosition = newShortPosition;
        t.shortAmount = shortAmount;
        t.longAmount = longAmount;
    }