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));
}
/**
* @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;
}
}
/**
* @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;
var coefficientsLength = coefficients.Length;
if (coefficientsLength > 1 && coefficients[0] == 0)
{
// Leading term must be non-zero for anything except the constant polynomial "0"
var 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;
}
}
