class NormalImpliedVolatilityFormula {

  public double getImpliedVolatility(final NormalFunctionData data, final EuropeanVanillaOption option, final double optionPrice) {
    final double numeraire = data.getNumeraire();
    final boolean isCall = option.isCall();
    final double f = data.getForward();
    final double k = option.getStrike();
    final double intrinsicPrice = numeraire * Math.max(0, (isCall ? 1 : -1) * (f - k));
    Validate.isTrue(optionPrice > intrinsicPrice || CompareUtils.closeEquals(optionPrice, intrinsicPrice, 1e-6), "option price (" + optionPrice + ") less than intrinsic value (" + intrinsicPrice
        + ")");
    if (Double.doubleToLongBits(optionPrice) == Double.doubleToLongBits(intrinsicPrice)) {
      return 0.0;
    }
    double sigma = (Math.abs(data.getNormalVolatility()) < 1E-10 ? 0.3 * f : data.getNormalVolatility());
    NormalFunctionData newData = new NormalFunctionData(f, numeraire, sigma);
    final double maxChange = 0.5 * f;
    double[] priceDerivative = new double[3];
    double price = NORMAL_PRICE_FUNCTION.getPriceAdjoint(option, newData, priceDerivative);
    double vega = priceDerivative[1];
    double change = (price - optionPrice) / vega;
    double sign = Math.signum(change);
    change = sign * Math.min(maxChange, Math.abs(change));
    if (change > 0 && change > sigma) {
      change = sigma;
    }
    int count = 0;
    while (Math.abs(change) > EPS) {
      sigma -= change;
      newData = new NormalFunctionData(f, numeraire, sigma);
      price = NORMAL_PRICE_FUNCTION.getPriceAdjoint(option, newData, priceDerivative);
      vega = priceDerivative[1];
      change = (price - optionPrice) / vega;
      sign = Math.signum(change);
      change = sign * Math.min(maxChange, Math.abs(change));
      if (change > 0 && change > sigma) {
        change = sigma;
      }
      if (count++ > MAX_ITERATIONS) {
        final BracketRoot bracketer = new BracketRoot();
        final BisectionSingleRootFinder rootFinder = new BisectionSingleRootFinder(EPS);
        final Function1D<Double, Double> func = new Function1D<Double, Double>() {
          @SuppressWarnings({"synthetic-access" })
          @Override
          public Double evaluate(final Double volatility) {
            final NormalFunctionData myData = new NormalFunctionData(data.getForward(), data.getNumeraire(), volatility);
            return NORMAL_PRICE_FUNCTION.getPriceFunction(option).evaluate(myData) - optionPrice;
          }
        };
        final double[] range = bracketer.getBracketedPoints(func, 0.0, 10.0);
        return rootFinder.getRoot(func, range[0], range[1]);
      }
    }
    return sigma;
  }

}