private int[] FindErrorLocations(GenericGfPoly errorLocator) { int numErrors = errorLocator.Degree; if (numErrors == 1) { return(new[] { errorLocator.GetCoefficient(1) }); } int[] result = new int[numErrors]; int e = 0; for (int i = 1; i < field.Size && e < numErrors; i++) { if (errorLocator.EvaluateAt(i) == 0) { result[e] = field.Inverse(i); e++; } } if (e != numErrors) { return(null); } return(result); }
internal GenericGfPoly[] RunEuclideanAlgorithm(GenericGfPoly a, GenericGfPoly b, int R) { 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; while (r.Degree >= R / 2) { GenericGfPoly rLastLast = rLast; GenericGfPoly tLastLast = tLast; rLast = r; tLast = t; if (rLast.IsZero) { 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) { return(null); } } int sigmaTildeAtZero = t.GetCoefficient(0); if (sigmaTildeAtZero == 0) { return(null); } int inverse = field.Inverse(sigmaTildeAtZero); GenericGfPoly sigma = t.Multiply(inverse); GenericGfPoly omega = r.Multiply(inverse); return(new[] { sigma, omega }); }