| static private AddOrSubtract ( int a, int b ) : int | ||
| a | int | |
| b | int | |
| Résultat | int | |
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());
}
var aCoefficients = coefficients;
var aLength = aCoefficients.Length;
var bCoefficients = other.coefficients;
var bLength = bCoefficients.Length;
var product = new int[aLength + bLength - 1];
for (var i = 0; i < aLength; i++)
{
var aCoeff = aCoefficients[i];
for (var j = 0; j < bLength; j++)
{
product[i + j] = GF256.AddOrSubtract(product[i + j],
field.Multiply(aCoeff, bCoefficients[j]));
}
}
return(new GF256Poly(field, product));
}
/**
* @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));
}
var size = coefficients.Length;
if (a == 1)
{
// Just the sum of the coefficients
var result2 = 0;
for (var i = 0; i < size; i++)
{
result2 = GF256.AddOrSubtract(result2, coefficients[i]);
}
return(result2);
}
var result = coefficients[0];
for (var i = 1; i < size; i++)
{
result = GF256.AddOrSubtract(field.Multiply(a, result), coefficients[i]);
}
return(result);
}
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);
}
var smallerCoefficients = coefficients;
var largerCoefficients = other.coefficients;
if (smallerCoefficients.Length > largerCoefficients.Length)
{
var temp = smallerCoefficients;
smallerCoefficients = largerCoefficients;
largerCoefficients = temp;
}
var sumDiff = new int[largerCoefficients.Length];
var 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 (var i = lengthDiff; i < largerCoefficients.Length; i++)
{
sumDiff[i] = GF256.AddOrSubtract(smallerCoefficients[i - lengthDiff], largerCoefficients[i]);
}
return(new GF256Poly(field, sumDiff));
}
