/// <summary> /// evaluation of this polynomial at a given point /// </summary> /// <param name="a">A.</param> /// <returns>evaluation of this polynomial at a given point</returns> internal int EvaluateAt(int a) { int result = 0; 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 foreach (var coefficient in coefficients) { result = GenericGf.AddOrSubtract(result, coefficient); } return(result); } result = coefficients[0]; for (int i = 1; i < size; i++) { result = GenericGf.AddOrSubtract(field.Multiply(a, result), coefficients[i]); } return(result); }
internal GenericGfPoly Multiply(GenericGfPoly other) { if (!field.Equals(other.field)) { throw new ArgumentException("GenericGFPolys do not have same GenericGF field"); } if (IsZero || other.IsZero) { 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] = GenericGf.AddOrSubtract(product[i + j], field.Multiply(aCoeff, bCoefficients[j])); } } return(new GenericGfPoly(field, product)); }
internal GenericGfPoly(GenericGf field, int[] coefficients) { if (coefficients.Length == 0) { throw new ArgumentException(); } this.field = field; int coefficientsLength = coefficients.Length; if (coefficientsLength > 1 && coefficients[0] == 0) { int firstNonZero = 1; while (firstNonZero < coefficientsLength && coefficients[firstNonZero] == 0) { firstNonZero++; } if (firstNonZero == coefficientsLength) { this.coefficients = new[] { 0 }; } else { this.coefficients = new int[coefficientsLength - firstNonZero]; Array.Copy(coefficients, firstNonZero, this.coefficients, 0, this.coefficients.Length); } } else { this.coefficients = coefficients; } }
internal GenericGfPoly AddOrSubtract(GenericGfPoly other) { if (!field.Equals(other.field)) { throw new ArgumentException("GenericGFPolys do not have same GenericGF 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 Array.Copy(largerCoefficients, 0, sumDiff, 0, lengthDiff); for (int i = lengthDiff; i < largerCoefficients.Length; i++) { sumDiff[i] = GenericGf.AddOrSubtract(smallerCoefficients[i - lengthDiff], largerCoefficients[i]); } return(new GenericGfPoly(field, sumDiff)); }
public ReedSolomonEncoder(GenericGf field) { this.field = field; this.cachedGenerators = new List <GenericGfPoly>(); cachedGenerators.Add(new GenericGfPoly(field, new[] { 1 })); }