internal GenericGfPoly[] Divide(GenericGfPoly other)
{
if (!field.Equals(other.field))
{
throw new ArgumentException("GenericGFPolys do not have same GenericGF field");
}
if (other.IsZero)
{
throw new ArgumentException("Divide by 0");
}
GenericGfPoly quotient = field.Zero;
GenericGfPoly remainder = this;
int denominatorLeadingTerm = other.GetCoefficient(other.Degree);
int inverseDenominatorLeadingTerm = field.Inverse(denominatorLeadingTerm);
while (remainder.Degree >= other.Degree && !remainder.IsZero)
{
int degreeDifference = remainder.Degree - other.Degree;
int scale = field.Multiply(remainder.GetCoefficient(remainder.Degree), inverseDenominatorLeadingTerm);
GenericGfPoly term = other.MultiplyByMonomial(degreeDifference, scale);
GenericGfPoly iterationQuotient = field.BuildMonomial(degreeDifference, scale);
quotient = quotient.AddOrSubtract(iterationQuotient);
remainder = remainder.AddOrSubtract(term);
}
return(new[] { quotient, remainder });
}
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));
}
public void Encode(int[] toEncode, int ecBytes)
{
if (ecBytes == 0)
{
return;
// throw new ArgumentException("No error correction bytes");
}
var dataBytes = toEncode.Length - ecBytes;
if (dataBytes <= 0)
{
return;
// throw new ArgumentException("No data bytes provided");
}
var generator = BuildGenerator(ecBytes);
var infoCoefficients = new int[dataBytes];
Array.Copy(toEncode, 0, infoCoefficients, 0, dataBytes);
var info = new GenericGfPoly(field, infoCoefficients);
info = info.MultiplyByMonomial(ecBytes, 1);
var remainder = info.Divide(generator)[1];
var coefficients = remainder.Coefficients;
var numZeroCoefficients = ecBytes - coefficients.Length;
for (var i = 0; i < numZeroCoefficients; i++)
{
toEncode[dataBytes + i] = 0;
}
Array.Copy(coefficients, 0, toEncode, dataBytes + numZeroCoefficients, coefficients.Length);
}
public GenericGf(int primitive, int size, int genBase)
{
this.primitive = primitive;
this.size = size;
this.generatorBase = genBase;
expTable = new int[size];
logTable = new int[size];
int x = 1;
for (int i = 0; i < size; i++)
{
expTable[i] = x;
x <<= 1; // x = x * 2;
if (x >= size)
{
x ^= primitive;
x &= size - 1;
}
}
for (int i = 0; i < size - 1; i++)
{
logTable[expTable[i]] = i;
}
zero = new GenericGfPoly(this, new[] { 0 });
one = new GenericGfPoly(this, new[] { 1 });
}
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));
}
