/// <returns> evaluation of this polynomial at a given point
/// </returns>
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 result = 0;
for (int i = 0; i < size; i++)
{
result = GF256.addOrSubtract(result, coefficients[i]);
}
return(result);
}
int result2 = coefficients[0];
for (int i = 1; i < size; i++)
{
result2 = GF256.addOrSubtract(field.multiply(a, result2), coefficients[i]);
}
return(result2);
}
/// <param name="field">the {@link GF256} instance representing the field to use
/// to perform computations
/// </param>
/// <param name="coefficients">coefficients as ints representing elements of GF(256), arranged
/// from most significant (highest-power term) coefficient to least significant
/// </param>
/// <throws> IllegalArgumentException if argument is null or empty, </throws>
/// <summary> or if leading coefficient is 0 and this is not a
/// constant polynomial (that is, it is not the monomial "0")
/// </summary>
internal GF256Poly(GF256 field, int[] coefficients)
{
if (coefficients == null || coefficients.Length == 0)
{
throw new System.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.Zero.coefficients;
}
else
{
this.coefficients = new int[coefficientsLength - firstNonZero];
Array.Copy(coefficients, firstNonZero, this.coefficients, 0, this.coefficients.Length);
}
}
else
{
this.coefficients = coefficients;
}
}
/// <param name="field">the {@link GF256} instance representing the field to use
/// to perform computations
/// </param>
/// <param name="coefficients">coefficients as ints representing elements of GF(256), arranged
/// from most significant (highest-power term) coefficient to least significant
/// </param>
/// <throws> IllegalArgumentException if argument is null or empty, </throws>
/// <summary> or if leading coefficient is 0 and this is not a
/// constant polynomial (that is, it is not the monomial "0")
/// </summary>
internal GF256Poly(GF256 field, int[] coefficients)
{
if (coefficients == null || coefficients.Length == 0)
{
throw new System.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.Zero.coefficients;
}
else
{
this.coefficients = new int[coefficientsLength - firstNonZero];
Array.Copy(coefficients, firstNonZero, this.coefficients, 0, this.coefficients.Length);
}
}
else
{
this.coefficients = coefficients;
}
}
internal GF256Poly multiply(GF256Poly other)
{
if (!field.Equals(other.field))
{
throw new System.ArgumentException("GF256Polys do not have same GF256 field");
}
if (Zero || other.Zero)
{
return(field.Zero);
}
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 System.ArgumentException("Only QR Code is supported at this time");
}
this.field = field;
this.cachedGenerators = System.Collections.ArrayList.Synchronized(new System.Collections.ArrayList(10));
cachedGenerators.Add(new GF256Poly(field, new int[]{1}));
}
public ReedSolomonEncoder(GF256 field)
{
if (!GF256.QR_CODE_FIELD.Equals(field))
{
throw new System.ArgumentException("Only QR Code is supported at this time");
}
this.field = field;
this.cachedGenerators = System.Collections.ArrayList.Synchronized(new System.Collections.ArrayList(10));
cachedGenerators.Add(new GF256Poly(field, new int[] { 1 }));
}
internal GF256Poly addOrSubtract(GF256Poly other)
{
if (!field.Equals(other.field))
{
throw new System.ArgumentException("GF256Polys do not have same GF256 field");
}
if (Zero)
{
return(other);
}
if (other.Zero)
{
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
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));
}
