/**
* 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];
}
}
private void checkQRRSDecode(int[] received) throws ReedSolomonException {
qrRSDecoder.decode(received, QR_CODE_ECC_BYTES);
for (int i = 0; i < QR_CODE_TEST.length; i++) {
assertEquals(received[i], QR_CODE_TEST[i]);
}
}