double normsdist(double x);

double normsinv(double x);

double ScInterpreter::normsdist(double x)

{

	return 0.5 + gauss(x);

}

double ScInterpreter::normsinv(double x)

{

    double y;

	if (x < 0.0 || x > 1.0)

    {

	    SetError(errIllegalArgument);

        y = 0.0;

    }

	else if (x == 0.0 || x == 1.0)

    {

        SetError(errNoValue);

        y = 0.0;

    }

	else

    {

        // Algorithm of #i32833#

        //

        // We have

        // normsdist(-5.99) =~= 0,000000001049

        // normsdist(5,99)  =~= 0,999999998951

        /* Outside the external borders of our searching segment, we use the

         * old method. We know the result will be with an accuracy better than

         * 1.10E-8. Inside, we use the new approach.

         */

        if (x <= 0.000000001049 || x >= 0.999999998951)

		    y = gaussinv(x);

        else

        {

            const double fEps = 1.10E-12;

            // set the searching segment

            double fMin = -5.99;

            double fMax =  5.99;

            double fMid;

            do

            {

                fMid = (fMin + fMax) / 2;

                double my_y = normsdist( fMid);

                if (::rtl::math::approxEqual( x, my_y))

                {

                    // jackpot, we're lucky, stop the algorithm

                    // y = fMid;   is done below after the loop

                    break;  // while

                }

                else

                {

                    if (x < my_y )

                        fMax = fMid;

                    else

                        fMin = fMid;

                }

            } while (fabs( fMin - fMax) > fEps);

            /* End of loop --> we know that  y  is in the segment

             * [ y - fMin-fEps, y + fMin-fEps] (with our definition of

             * the normal standard law normsdist, not the real law). It means

             * that we're sure that normsdist(norminv(x)) and x have the same 7

             * decimals, and probably more.

             */

            y = fMid;

        }

    }

	return y;

}