private Polynomial MultiplyKaratsuba(double[] leftCoefficients, double[] rightCoefficients, int leftOrder, int rightOrder, int n, int offset)
{
if (n == 1)
{
return(new Polynomial(new double[] { leftCoefficients[offset] * rightCoefficients[offset] }));
}
if (n == 2)
{
return(new Polynomial(new double[] { leftCoefficients[offset] * rightCoefficients[offset], leftCoefficients[offset] * rightCoefficients[offset + 1] + leftCoefficients[offset + 1] * rightCoefficients[offset], leftCoefficients[offset + 1] * rightCoefficients[offset + 1] }));
}
n >>= 1;
double[] FF = new double[n], GG = new double[n];
for (int i = offset; i < n + offset; i++)
{
FF[i - offset] = leftCoefficients[i] + leftCoefficients[n + i];
GG[i - offset] = rightCoefficients[i] + rightCoefficients[n + i];
}
Polynomial FG0 = MultiplyKaratsuba(leftCoefficients, rightCoefficients, n - 1, n - 1, n, offset);
Polynomial FG1 = MultiplyKaratsuba(leftCoefficients, rightCoefficients, Math.Max(leftOrder - n, 0), Math.Max(rightOrder - n, 0), n, offset + n);
Polynomial FFGG = MultiplyKaratsuba(FF, GG, n - 1, n - 1, n, 0);
FFGG.SubtractInplace(FG0);
FFGG.SubtractInplace(FG1);
FFGG.MultiplyShiftInplace(n);
FG1.MultiplyShiftInplace(n + n);
FG1.AddInplace(FFGG);
FG1.AddInplace(FG0);
return(FG1);
}