internal static void TraceImage
(
Pdf417Decoder Pdf417Decoder,
int CenterX,
int CenterY,
int Left,
int Top,
int Right,
int Bottom
)
{
int Width = Left + Right + 1;
int Height = Top + Bottom + 1;
int OrgX = CenterX - Left;
int OrgY = CenterY - Top;
char[] Line = new char[Width + 1];
for (int Y = 0; Y < Height; Y++)
{
Line[0] = Y == Top ? '>' : ' ';
int R = OrgY + Y;
for (int X = 0; X < Width; X++)
{
int C = OrgX + X;
if (R < 0 || R >= Pdf417Decoder.ImageHeight || C < 0 || C >= Pdf417Decoder.ImageWidth)
{
Line[X + 1] = ' ';
}
else
{
Line[X + 1] = Pdf417Decoder.ImageMatrix[R, C] ? 'X' : '.';
}
}
Pdf417Trace.Write(new string(Line));
}
return;
}
// Decode the received codewords
internal static int TestCodewords
(
int[] Codewords,
int ErrorCorrectionLength
)
{
// create codewords polynomial
Polynomial PolyCodewords = new Polynomial(Codewords);
// create syndrom coefficients array
int[] Syndrome = new int[ErrorCorrectionLength];
// assume no errors
bool Error = false;
// test for errors
// if the syndrom array is all zeros, there is no error
for (int Index = ErrorCorrectionLength; Index > 0; Index--)
{
if ((Syndrome[ErrorCorrectionLength - Index] = PolyCodewords.EvaluateAt(Modulus.ExpTable[Index])) != 0)
{
Error = true;
}
}
// no errors
if (!Error)
{
return(0);
}
// convert syndrom array to polynomial
Polynomial PolySyndrome = new Polynomial(Syndrome);
// Greatest Common Divisor (return -1 if error cannot be corrected)
if (!EuclideanAlgorithm(ErrorCorrectionLength, PolySyndrome,
out Polynomial ErrorLocator, out Polynomial ErrorEvaluator))
{
return(-1);
}
// error locator (return -1 if error cannot be corrected)
int[] ErrorLocations = FindErrorLocations(ErrorLocator);
if (ErrorLocations == null)
{
return(-1);
}
// formal derivatives
Polynomial FormalDerivative = FindFormalDerivatives(ErrorLocator);
// This is directly applying Forney's Formula
int Errors = ErrorLocations.Length;
for (int Index = 0; Index < Errors; Index++)
{
// error location
int ErrLoc = ErrorLocations[Index];
// error position (return -1 if error cannot be corrected)
int ErrPos = Codewords.Length - 1 - Modulus.LogTable[Modulus.Inverse(ErrLoc)];
if (ErrPos < 0)
{
return(-1);
}
// error magnitude
int ErrorMagnitude = Modulus.Divide(Modulus.Negate(ErrorEvaluator.EvaluateAt(ErrLoc)), FormalDerivative.EvaluateAt(ErrLoc));
// correct codeword
Codewords[ErrPos] = Modulus.Subtract(Codewords[ErrPos], ErrorMagnitude);
// save error position in error locations array
ErrorLocations[Index] = ErrPos;
}
#if DEBUG && ERRCORRECT
Array.Sort(ErrorLocations);
StringBuilder Str1 = new StringBuilder();
for (int Row = 0; Row < DataRows; Row++)
{
Str1.Clear();
Str1.AppendFormat("{0}: ", Row);
for (int Col = 1; Col <= DataColumns; Col++)
{
int Pos = DataColumns * Row + Col - 1;
int Index = Array.BinarySearch(ErrorLocations, Pos);
if (Index < 0)
{
Str1.AppendFormat("{0}, ", Codewords[Pos]);
}
else
{
Str1.AppendFormat("{0}*, ", Codewords[Pos]);
}
}
Pdf417Trace.Write(Str1.ToString());
}
#endif
// message was successfuly repaired
return(Errors);
}