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 });
}