/**
* Verify that all is OK with the codeword array.
*
* @param codewords
* @return an index to the first data codeword.
* @throws FormatException
*/
private static void verifyCodewordCount(int[] codewords, int numECCodewords)
throws FormatException {
if (codewords.length < 4) {
// Codeword array size should be at least 4 allowing for
// Count CW, At least one Data CW, Error Correction CW, Error Correction CW
throw FormatException.getFormatInstance();
}
// The first codeword, the Symbol Length Descriptor, shall always encode the total number of
// data
// codewords in the symbol, including the Symbol Length Descriptor itself, data codewords and
// pad
// codewords, but excluding the number of error correction codewords.
int numberOfCodewords = codewords[0];
if (numberOfCodewords > codewords.length) {
throw FormatException.getFormatInstance();
}
if (numberOfCodewords == 0) {
// Reset to the length of the array - 8 (Allow for at least level 3 Error Correction (8 Error
// Codewords)
if (numECCodewords < codewords.length) {
codewords[0] = codewords.length - numECCodewords;
} else {
throw FormatException.getFormatInstance();
}
}
}
/**
* Given data and error-correction codewords received, possibly corrupted by errors, attempts to
* correct the errors in-place using Reed-Solomon error correction.
*
* @param codewords data and error correction codewords
* @throws ChecksumException if error correction fails
*/
private static int correctErrors(int[] codewords, int[] erasures, int numECCodewords)
throws FormatException {
if ((erasures != null && erasures.length > numECCodewords / 2 + MAX_ERRORS)
|| (numECCodewords < 0 || numECCodewords > MAX_EC_CODEWORDS)) {
// Too many errors or EC Codewords is corrupted
throw FormatException.getFormatInstance();
}
// Try to correct the errors
// TODO enable error correction
int result = 0; // rsDecoder.correctErrors(codewords, numECCodewords);
if (erasures != null) {
int numErasures = erasures.length;
if (result > 0) {
numErasures -= result;
}
if (numErasures > MAX_ERRORS) {
// Still too many errors
throw FormatException.getFormatInstance();
}
}
return result;
}
/**
* Decodes a PDF417 Code represented as a {@link BitMatrix}. A 1 or "true" is taken to mean a
* black module.
*
* @param bits booleans representing white/black PDF417 Code modules
* @return text and bytes encoded within the PDF417 Code
* @throws FormatException if the PDF417 Code cannot be decoded
*/
public DecoderResult decode(BitMatrix bits) throws FormatException {
// Construct a parser to read the data codewords and error-correction level
BitMatrixParser parser = new BitMatrixParser(bits);
int[] codewords = parser.readCodewords();
if (codewords == null || codewords.length == 0) {
throw FormatException.getFormatInstance();
}
int ecLevel = parser.getECLevel();
int numECCodewords = 1 << (ecLevel + 1);
int[] erasures = parser.getErasures();
correctErrors(codewords, erasures, numECCodewords);
verifyCodewordCount(codewords, numECCodewords);
// Decode the codewords
return DecodedBitStreamParser.decode(codewords);
}
