/// <summary>
/// The evaluate at.
/// </summary>
/// <param name="a">
/// The a.
/// </param>
/// <returns>
/// The <see cref="int"/>.
/// </returns>
public int EvaluateAt(int a)
{
// Just return the x^0 coefficient
if (a == 0)
{
return(this.GetCoefficient(0));
}
int size = this.coefficients.Length;
if (a == 1)
{
// Just the sum of the coefficients
int txt = 0;
for (int i = 0; i < size; i++)
{
txt = QrGaloisField.AddOrSubtract(txt, this.coefficients[i]);
}
return(txt);
}
int res = this.coefficients[0];
for (int i = 1; i < size; i++)
{
res = QrGaloisField.AddOrSubtract(this.field.Multiply(a, res), this.coefficients[i]);
}
return(res);
}
/// <summary>
/// The multiply.
/// </summary>
/// <param name="other">
/// The other.
/// </param>
/// <returns>
/// The <see cref="QrGaloisFieldPoly"/>.
/// </returns>
public QrGaloisFieldPoly Multiply(QrGaloisFieldPoly other)
{
if (this.IsZero() || other.IsZero())
{
return(this.field.Zero);
}
int[] galoisACoefficients = this.coefficients;
int galoisALength = galoisACoefficients.Length;
int[] galoisBCoefficients = other.coefficients;
int galoisBLength = galoisBCoefficients.Length;
int[] product = new int[galoisALength + galoisBLength - 1];
for (int i = 0; i < galoisALength; i++)
{
int galoisACoeff = galoisACoefficients[i];
for (int j = 0; j < galoisBLength; j++)
{
product[i + j] = QrGaloisField.AddOrSubtract(product[i + j], this.field.Multiply(galoisACoeff, galoisBCoefficients[j]));
}
}
return(new QrGaloisFieldPoly(this.field, product));
}
/// <summary>
/// The add or subtract.
/// </summary>
/// <param name="other">
/// The other.
/// </param>
/// <returns>
/// The <see cref="QrGaloisFieldPoly"/>.
/// </returns>
public QrGaloisFieldPoly AddOrSubtract(QrGaloisFieldPoly other)
{
if (this.IsZero())
{
return(other);
}
if (other.IsZero())
{
return(this);
}
int[] smallerCoefficients = this.coefficients;
int[] largerCoefficients = other.coefficients;
if (smallerCoefficients.Length > largerCoefficients.Length)
{
int[] temp = smallerCoefficients;
smallerCoefficients = largerCoefficients;
largerCoefficients = temp;
}
int[] sumDiff = new int[largerCoefficients.Length];
int lengthDiff = largerCoefficients.Length - smallerCoefficients.Length;
// Copy high-order terms only found in higher-power polynomial's coefficients
Array.Copy(largerCoefficients, 0, sumDiff, 0, lengthDiff);
for (int i = lengthDiff; i < largerCoefficients.Length; i++)
{
sumDiff[i] = QrGaloisField.AddOrSubtract(smallerCoefficients[i - lengthDiff], largerCoefficients[i]);
}
return(new QrGaloisFieldPoly(this.field, sumDiff));
}