internal GenericGFPoly[] Divide(GenericGFPoly other)
        {
            if (field.Equals(other.field) == false)
            {
                throw new ArgumentException("GenericGFPolys do not have same GenericGF field");
            }

            if (other.IsZero)
            {
                throw new ArgumentException("Divide by 0");
            }

            GenericGFPoly quotient  = field.Zero;
            GenericGFPoly remainder = this;

            int denominatorLeadingTerm        = other.GetCoefficient(other.Degree);
            int inverseDenominatorLeadingTerm = field.Inverse(denominatorLeadingTerm);

            while (remainder.Degree >= other.Degree && !remainder.IsZero)
            {
                int           degreeDifference  = remainder.Degree - other.Degree;
                int           scale             = field.Multiply(remainder.GetCoefficient(remainder.Degree), inverseDenominatorLeadingTerm);
                GenericGFPoly term              = other.MultiplyByMonomial(degreeDifference, scale);
                GenericGFPoly iterationQuotient = field.BuildMonomial(degreeDifference, scale);

                quotient  = quotient.AddOrSubtract(iterationQuotient);
                remainder = remainder.AddOrSubtract(term);
            }

            return(new GenericGFPoly[] { quotient, remainder });
        }
Exemplo n.º 2
0
        internal GenericGFPoly[] RunEuclideanAlgorithm(GenericGFPoly a, GenericGFPoly b, int R)
        {
            // Assume a's degree is >= b's
            if (a.Degree < b.Degree)
            {
                GenericGFPoly temp = a;
                a = b;
                b = temp;
            }

            GenericGFPoly rLast = a;
            GenericGFPoly r     = b;
            GenericGFPoly tLast = field.Zero;
            GenericGFPoly t     = field.One;

            int halfR = R / 2;

            // Run Euclidean algorithm until r's degree is less than R/2
            while (r.Degree >= halfR)
            {
                GenericGFPoly rLastLast = rLast;
                GenericGFPoly tLastLast = tLast;

                rLast = r;
                tLast = t;

                // Divide rLastLast by rLast, with quotient in q and remainder in r
                if (rLast.IsZero)
                {
                    // Oops, Euclidean algorithm already terminated?
                    // throw new ReedSolomonException("r_{i-1} was zero");
                    return(null);
                }

                r = rLastLast;

                GenericGFPoly q = field.Zero;
                int           denominatorLeadingTerm = rLast.GetCoefficient(rLast.Degree);
                int           dltInverse             = field.Inverse(denominatorLeadingTerm);

                while (r.Degree >= rLast.Degree && !r.IsZero)
                {
                    int degreeDiff = r.Degree - rLast.Degree;
                    int scale      = field.Multiply(r.GetCoefficient(r.Degree), dltInverse);
                    q = q.AddOrSubtract(field.BuildMonomial(degreeDiff, scale));
                    r = r.AddOrSubtract(rLast.MultiplyByMonomial(degreeDiff, scale));
                }

                t = q.Multiply(tLast).AddOrSubtract(tLastLast);

                if (r.Degree >= rLast.Degree)
                {
                    // throw new IllegalStateException("Division algorithm failed to reduce polynomial?");
                    return(null);
                }
            }

            int sigmaTildeAtZero = t.GetCoefficient(0);

            if (sigmaTildeAtZero == 0)
            {
                // throw new ReedSolomonException("sigmaTilde(0) was zero");
                return(null);
            }

            int           inverse = field.Inverse(sigmaTildeAtZero);
            GenericGFPoly sigma   = t.Multiply(inverse);
            GenericGFPoly omega   = r.Multiply(inverse);

            return(new GenericGFPoly[] { sigma, omega });
        }