/**
* @return evaluation of this polynomial at a given point
*/
internal int EvaluateAt(int a)
{
if (a == 0)
{
// Just return the x^0 coefficient
return(GetCoefficient(0));
}
int size = coefficients.Length;
if (a == 1)
{
// Just the sum of the coefficients
int result2 = 0;
for (int i = 0; i < size; i++)
{
result2 = GF256.AddOrSubtract(result2, coefficients[i]);
}
return(result2);
}
int result = coefficients[0];
for (int i = 1; i < size; i++)
{
result = GF256.AddOrSubtract(field.Multiply(a, result), coefficients[i]);
}
return(result);
}
internal GF256Poly Multiply(GF256Poly other)
{
if (!field.Equals(other.field))
{
throw new ArgumentException("GF256Polys do not have same GF256 field");
}
if (IsZero() || other.IsZero())
{
return(field.GetZero());
}
int[] aCoefficients = this.coefficients;
int aLength = aCoefficients.Length;
int[] bCoefficients = other.coefficients;
int bLength = bCoefficients.Length;
int[] product = new int[aLength + bLength - 1];
for (int i = 0; i < aLength; i++)
{
int aCoeff = aCoefficients[i];
for (int j = 0; j < bLength; j++)
{
product[i + j] = GF256.AddOrSubtract(product[i + j],
field.Multiply(aCoeff, bCoefficients[j]));
}
}
return(new GF256Poly(field, product));
}
public ReedSolomonEncoder(GF256 field)
{
if (!GF256.QR_CODE_FIELD.Equals(field))
{
throw new ArgumentException("Only QR Code is supported at this time");
}
this.field = field;
this.cachedGenerators = new List <GF256Poly>();
cachedGenerators.Add(new GF256Poly(field, new int[] { 1 }));
}
/**
* @param field the {@link GF256} instance representing the field to use
* to perform computations
* @param coefficients coefficients as ints representing elements of GF(256), arranged
* from most significant (highest-power term) coefficient to least significant
* @throws IllegalArgumentException if argument is null or empty,
* or if leading coefficient is 0 and this is not a
* constant polynomial (that is, it is not the monomial "0")
*/
internal GF256Poly(GF256 field, int[] coefficients)
{
if (coefficients == null || coefficients.Length == 0)
{
throw new ArgumentException();
}
this.field = field;
int coefficientsLength = coefficients.Length;
if (coefficientsLength > 1 && coefficients[0] == 0)
{
// Leading term must be non-zero for anything except the constant polynomial "0"
int firstNonZero = 1;
while (firstNonZero < coefficientsLength && coefficients[firstNonZero] == 0)
{
firstNonZero++;
}
if (firstNonZero == coefficientsLength)
{
this.coefficients = field.GetZero().coefficients;
}
else
{
this.coefficients = new int[coefficientsLength - firstNonZero];
System.Array.Copy(coefficients,
firstNonZero,
this.coefficients,
0,
this.coefficients.Length);
}
}
else
{
this.coefficients = coefficients;
}
}
internal GF256Poly AddOrSubtract(GF256Poly other)
{
if (!field.Equals(other.field))
{
throw new ArgumentException("GF256Polys do not have same GF256 field");
}
if (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-degree polynomial's coefficients
System.Array.Copy(largerCoefficients, 0, sumDiff, 0, lengthDiff);
for (int i = lengthDiff; i < largerCoefficients.Length; i++)
{
sumDiff[i] = GF256.AddOrSubtract(smallerCoefficients[i - lengthDiff], largerCoefficients[i]);
}
return(new GF256Poly(field, sumDiff));
}