public String toString()
{
StringBuilder result = new StringBuilder(8 * getDegree());
for (int degree = getDegree(); degree >= 0; degree--)
{
int coefficient = getCoefficient(degree);
if (coefficient != 0)
{
if (coefficient < 0)
{
result.Append(" - ");
coefficient = -coefficient;
}
else
{
if (result.Length > 0)
{
result.Append(" + ");
}
}
if (degree == 0 || coefficient != 1)
{
int alphaPower = field.log(coefficient);
if (alphaPower == 0)
{
result.Append('1');
}
else if (alphaPower == 1)
{
result.Append('a');
}
else
{
result.Append("a^");
result.Append(alphaPower);
}
}
if (degree != 0)
{
if (degree == 1)
{
result.Append('x');
}
else
{
result.Append("x^");
result.Append(degree);
}
}
}
}
return(result.ToString());
}
/**
* <p>Decodes given set of received codewords, which include both data and error-correction
* codewords. Really, this means it uses Reed-Solomon to detect and correct errors, in-place,
* in the input.</p>
*
* @param received data and error-correction codewords
* @param twoS number of error-correction codewords available
* @throws ReedSolomonException if decoding fails for any reason
*/
public void decode(int[] received, int twoS)
{
try{
GF256Poly poly = new GF256Poly(field, received);
int[] syndromeCoefficients = new int[twoS];
bool dataMatrix = field.Equals(GF256.DATA_MATRIX_FIELD);
bool noError = true;
for (int i = 0; i < twoS; i++)
{
// Thanks to sanfordsquires for this fix:
int eval = poly.evaluateAt(field.exp(dataMatrix ? i + 1 : i));
syndromeCoefficients[syndromeCoefficients.Length - 1 - i] = eval;
if (eval != 0)
{
noError = false;
}
}
if (noError)
{
return;
}
GF256Poly syndrome = new GF256Poly(field, syndromeCoefficients);
GF256Poly[] sigmaOmega =
runEuclideanAlgorithm(field.buildMonomial(twoS, 1), syndrome, twoS);
GF256Poly sigma = sigmaOmega[0];
GF256Poly omega = sigmaOmega[1];
int[] errorLocations = findErrorLocations(sigma);
int[] errorMagnitudes = findErrorMagnitudes(omega, errorLocations, dataMatrix);
for (int i = 0; i < errorLocations.Length; i++)
{
int position = received.Length - 1 - field.log(errorLocations[i]);
if (position < 0)
{
throw new ReedSolomonException("Bad error location");
}
received[position] = GF256.addOrSubtract(received[position], errorMagnitudes[i]);
}
}catch (ReedSolomonException e) {
throw new ReedSolomonException(e.Message);
}
}
