JavaScript IRR 算法

function IRR(cashFlows, estimatedResult) {
    var result = "isNAN";
    if (cashFlows != null && cashFlows.length > 0) {
        // check if business startup costs is not zero:
        if (cashFlows[0] != 0) {
            var noOfCashFlows = cashFlows.length;
            var sumCashFlows = 0;
            // check if at least 1 positive and 1 negative cash flow exists:
            var noOfNegativeCashFlows = 0;
            var noOfPositiveCashFlows = 0;
            for (var i = 0; i < noOfCashFlows; i++) {
                sumCashFlows += cashFlows[i];
                if (cashFlows[i] > 0) {
                    noOfPositiveCashFlows++;
                } else {
                    if (cashFlows[i] < 0) {
                        noOfNegativeCashFlows++;
                    }
                }
            }

            // at least 1 negative and 1 positive cash flow available?
            if (noOfNegativeCashFlows > 0 && noOfPositiveCashFlows > 0) {
                // set estimated result:
                var irrGuess = 0.1; // default: 10%
                if (!isNaN(estimatedResult)) {
                    irrGuess = estimatedResult;
                    if (irrGuess <= 0) {
                        irrGuess = 0.5;
                    }
                }

                // initialize first IRR with estimated result:
                var irr = 0;
                if (sumCashFlows < 0) { // sum of cash flows negative?
                    irr = -irrGuess;
                } else { // sum of cash flows not negative
                    irr = irrGuess;
                }

                // iteration:
                // the smaller the distance, the smaller the interpolation
                // error
                var minDistance = 1e-15;

                // business startup costs
                var cashFlowStart = cashFlows[0];
                var maxIteration = 100;
                var wasHi = false;
                var cashValue = 0;
                for (var i = 0; i <= maxIteration; i++) {
                    // calculate cash value with current irr:
                    cashValue = cashFlowStart; // init with startup costs

                    // for each cash flow
                    for (var j = 1; j < noOfCashFlows; j++) {
                        cashValue += cashFlows[j] / Math.pow(1 + irr, j);
                    }

                    // cash value is nearly zero
                    if (Math.abs(cashValue) < 0.01) {
                        result = irr;
                        break;
                    }

                    // adjust irr for next iteration:
                    // cash value > 0 => next irr > current irr
                    if (cashValue > 0) {
                        if (wasHi) {
                            irrGuess /= 2;
                        }
                        irr += irrGuess;
                        if (wasHi) {
                            irrGuess -= minDistance;
                            wasHi = false;
                        }
                    } else {// cash value < 0 => next irr < current irr
                        irrGuess /= 2;
                        irr -= irrGuess;
                        wasHi = true;
                    }

                    // estimated result too small to continue => end
                    // calculation
                    if (irrGuess <= minDistance) {
                        result = irr;
                        break;
                    }
                }
            }
        }
    }
    return result;
}