public void T05_PolynomialMultiplication()
{
GF2pField field = new GF2pField(8);
GF2pPolynomial a = new GF2pPolynomial(field, 0, 4, 17, 0, 9), b = new GF2pPolynomial(field, 19, 11, 0, 100);
Assert.AreEqual(new GF2pPolynomial(field, 0, 76, 18, 187, 6, 57, 0, 99), a * b);
Assert.AreEqual(a * b, b * a);
Assert.AreEqual(new GF2pPolynomial(field, 0), new GF2pPolynomial(field, 0) * a);
Assert.AreEqual(new GF2pPolynomial(field, 0), default(GF2pPolynomial) * b);
Assert.AreEqual(new GF2pPolynomial(field, 121, 49, 0, 33), b * 7);
Assert.AreEqual(0, GF2pPolynomial.MultiplyAt(a, b, 0));
Assert.AreEqual(76, GF2pPolynomial.MultiplyAt(a, b, 1));
Assert.AreEqual(18, GF2pPolynomial.MultiplyAt(a, b, 2));
Assert.AreEqual(187, GF2pPolynomial.MultiplyAt(a, b, 3));
Assert.AreEqual(6, GF2pPolynomial.MultiplyAt(a, b, 4));
Assert.AreEqual(57, GF2pPolynomial.MultiplyAt(a, b, 5));
Assert.AreEqual(0, GF2pPolynomial.MultiplyAt(a, b, 6));
Assert.AreEqual(99, GF2pPolynomial.MultiplyAt(a, b, 7));
Assert.AreEqual(0, GF2pPolynomial.MultiplyAt(a, b, 8));
Assert.AreEqual(0, GF2pPolynomial.MultiplyAt(a, b, 9));
Assert.AreEqual(0, a.MultiplyAt(b, 0));
Assert.AreEqual(76, a.MultiplyAt(b, 1));
Assert.AreEqual(18, a.MultiplyAt(b, 2));
Assert.AreEqual(187, a.MultiplyAt(b, 3));
}
static void BerlekampMassey(GF2pPolynomial syndromes, GF2pPolynomial erasureLocator, GF2pPolynomial erasureEvaluator, int erasureCount,
out GF2pPolynomial errataLocator, out GF2pPolynomial errataEvaluator)
{
GF2pPolynomial locator, prevLocator, evaluator, prevEvaluator, a, b;
if (erasureCount != 0)
{
locator = erasureLocator;
a = evaluator = erasureEvaluator;
}
else
{
evaluator = locator = new GF2pPolynomial(syndromes.Field, 1);
a = new GF2pPolynomial(syndromes.Field, 0);
}
b = locator;
int L = 0;
for (int i = 0, count = syndromes.Length - erasureCount; i < count; i++)
{
int k = i + erasureCount, delta = GF2pPolynomial.MultiplyAt(syndromes, locator, k);
prevLocator = locator;
prevEvaluator = evaluator;
GF2pPolynomial shiftA = a << 1, shiftB = b << 1;
locator += shiftB * delta;
evaluator += shiftA * delta;
if (delta == 0 || 2 * L > k + erasureCount + 1)
{
b = shiftB;
a = shiftA;
}
else
{
b = prevLocator / delta;
a = prevEvaluator / delta;
L = k + 1 - L;
}
}
if (evaluator.Length > locator.Length)
{
evaluator = evaluator.Truncate(locator.Length);
}
evaluator = CalculateErrorEvaluator(syndromes, locator);
errataLocator = locator;
errataEvaluator = evaluator;
}
