public new IntegerPolynomial Multiply(IntegerPolynomial poly2, int modulus)
{
// even on 32-bit systems, LongPolynomial5 multiplies faster than IntegerPolynomial
if (modulus == 2048)
{
IntegerPolynomial poly2Pos = (IntegerPolynomial)poly2.Clone();
poly2Pos.ModPositive(2048);
LongPolynomial5 poly5 = new LongPolynomial5(poly2Pos);
return(poly5.Multiply(this).ToIntegerPolynomial());
}
else
{
return(base.Multiply(poly2, modulus));
}
}
/**
* Karazuba multiplication
*/
private IntegerPolynomial MultiplyRecursive(IntegerPolynomial poly2)
{
int[] a = coeffs;
int[] b = poly2.coeffs;
int n = poly2.coeffs.Length;
if (n <= 32)
{
int cn = 2 * n - 1;
IntegerPolynomial c = new IntegerPolynomial(new int[cn]);
for (int k = 0; k < cn; k++)
{
for (int i = System.Math.Max(0, k - n + 1); i <= System.Math.Min(k, n - 1); i++)
{
c.coeffs[k] += b[i] * a[k - i];
}
}
return(c);
}
else
{
int n1 = n / 2;
int[] a1temp = new int[n1];
int[] a2temp = new int[n - n1];
int[] b1temp = new int[n1];
int[] b2temp = new int[n - n1];
Array.Copy(a, a1temp, n1);
Array.Copy(a, n1, a2temp, 0, n - n1);
Array.Copy(b, b1temp, n1);
Array.Copy(b, n1, b2temp, 0, n - n1);
IntegerPolynomial a1 = new IntegerPolynomial(a1temp);
IntegerPolynomial a2 = new IntegerPolynomial(a2temp);
IntegerPolynomial b1 = new IntegerPolynomial(b1temp);
IntegerPolynomial b2 = new IntegerPolynomial(b2temp);
IntegerPolynomial A = (IntegerPolynomial)a1.Clone();
A.Add(a2);
IntegerPolynomial B = (IntegerPolynomial)b1.Clone();
B.Add(b2);
IntegerPolynomial c1 = a1.MultiplyRecursive(b1);
IntegerPolynomial c2 = a2.MultiplyRecursive(b2);
IntegerPolynomial c3 = A.MultiplyRecursive(B);
c3.Sub(c1);
c3.Sub(c2);
IntegerPolynomial c = new IntegerPolynomial(2 * n - 1);
for (int i = 0; i < c1.coeffs.Length; i++)
{
c.coeffs[i] = c1.coeffs[i];
}
for (int i = 0; i < c3.coeffs.Length; i++)
{
c.coeffs[n1 + i] += c3.coeffs[i];
}
for (int i = 0; i < c2.coeffs.Length; i++)
{
c.coeffs[2 * n1 + i] += c2.coeffs[i];
}
return(c);
}
}