private static void checkOneChecksum(CharSequence result, int checkPosition, int weightMax)
throws ChecksumException {
int weight = 1;
int total = 0;
for (int i = checkPosition - 1; i >= 0; i--) {
total += weight * ALPHABET_STRING.indexOf(result.charAt(i));
if (++weight > weightMax) {
weight = 1;
}
}
if (result.charAt(checkPosition) != ALPHABET[total % 47]) {
throw ChecksumException.getChecksumInstance();
}
}
/**
* Given data and error-correction codewords received, possibly corrupted by errors, attempts to
* correct the errors in-place using Reed-Solomon error correction.
*
* @param codewordBytes data and error correction codewords
* @param numDataCodewords number of codewords that are data bytes
* @throws ChecksumException if error correction fails
*/
private void correctErrors(byte[] codewordBytes, int numDataCodewords) throws ChecksumException {
int numCodewords = codewordBytes.length;
// First read into an array of ints
int[] codewordsInts = new int[numCodewords];
for (int i = 0; i < numCodewords; i++) {
codewordsInts[i] = codewordBytes[i] & 0xFF;
}
try {
rsDecoder.decode(codewordsInts, codewordBytes.length - numDataCodewords);
} catch (ReedSolomonException ignored) {
throw ChecksumException.getChecksumInstance();
}
// Copy back into array of bytes -- only need to worry about the bytes that were data
// We don't care about errors in the error-correction codewords
for (int i = 0; i < numDataCodewords; i++) {
codewordBytes[i] = (byte) codewordsInts[i];
}
}
@Override
public Result decodeRow(int rowNumber, BitArray row, Map<DecodeHintType, ?> hints)
throws NotFoundException, ChecksumException, FormatException {
int[] counters = new int[9];
int[] start = findAsteriskPattern(row, counters);
// Read off white space
int nextStart = row.getNextSet(start[1]);
int end = row.getSize();
StringBuilder result = new StringBuilder(20);
char decodedChar;
int lastStart;
do {
recordPattern(row, nextStart, counters);
int pattern = toNarrowWidePattern(counters);
if (pattern < 0) {
throw NotFoundException.getNotFoundInstance();
}
decodedChar = patternToChar(pattern);
result.append(decodedChar);
lastStart = nextStart;
for (int counter : counters) {
nextStart += counter;
}
// Read off white space
nextStart = row.getNextSet(nextStart);
} while (decodedChar != '*');
result.setLength(result.length() - 1); // remove asterisk
// Look for whitespace after pattern:
int lastPatternSize = 0;
for (int counter : counters) {
lastPatternSize += counter;
}
int whiteSpaceAfterEnd = nextStart - lastStart - lastPatternSize;
// If 50% of last pattern size, following last pattern, is not whitespace, fail
// (but if it's whitespace to the very end of the image, that's OK)
if (nextStart != end && (whiteSpaceAfterEnd >> 1) < lastPatternSize) {
throw NotFoundException.getNotFoundInstance();
}
if (usingCheckDigit) {
int max = result.length() - 1;
int total = 0;
for (int i = 0; i < max; i++) {
total += ALPHABET_STRING.indexOf(result.charAt(i));
}
if (result.charAt(max) != ALPHABET[total % 43]) {
throw ChecksumException.getChecksumInstance();
}
result.setLength(max);
}
if (result.length() == 0) {
// false positive
throw NotFoundException.getNotFoundInstance();
}
String resultString;
if (extendedMode) {
resultString = decodeExtended(result);
} else {
resultString = result.toString();
}
float left = (float) (start[1] + start[0]) / 2.0f;
float right = (float) (nextStart + lastStart) / 2.0f;
return new Result(
resultString,
null,
new ResultPoint[] {
new ResultPoint(left, (float) rowNumber), new ResultPoint(right, (float) rowNumber)
},
BarcodeFormat.CODE_39);
}