interleaveWithECBytes static method

BitArray interleaveWithECBytes(BitArray bits, int numTotalBytes, int numDataBytes, int numRSBlocks,)

Interleave "bits" with corresponding error correction bytes. On success, store the result in "result". The interleave rule is complicated. See 8.6 of JISX0510:2004 (p.37) for details.

Implementation

static BitArray interleaveWithECBytes(
  BitArray bits,
  int numTotalBytes,
  int numDataBytes,
  int numRSBlocks,
) {
  // "bits" must have "getNumDataBytes" bytes of data.
  if (bits.sizeInBytes != numDataBytes) {
    throw WriterException('Number of bits and data bytes does not match');
  }

  // Step 1.  Divide data bytes into blocks and generate error correction bytes for them. We'll
  // store the divided data bytes blocks and error correction bytes blocks into "blocks".
  int dataBytesOffset = 0;
  int maxNumDataBytes = 0;
  int maxNumEcBytes = 0;

  // Since, we know the number of reedsolmon blocks, we can initialize the vector with the number.
  final blocks = <BlockPair>[]; //numRSBlocks

  for (int i = 0; i < numRSBlocks; ++i) {
    final numDataBytesInBlock = [0];
    final numEcBytesInBlock = [0];
    getNumDataBytesAndNumECBytesForBlockID(
      numTotalBytes,
      numDataBytes,
      numRSBlocks,
      i,
      numDataBytesInBlock,
      numEcBytesInBlock,
    );

    final size = numDataBytesInBlock[0];
    final dataBytes = Uint8List(size);
    bits.toBytes(8 * dataBytesOffset, dataBytes, 0, size);
    final ecBytes = generateECBytes(dataBytes, numEcBytesInBlock[0]);
    blocks.add(BlockPair(dataBytes, ecBytes));

    maxNumDataBytes = math.max(maxNumDataBytes, size);
    maxNumEcBytes = math.max(maxNumEcBytes, ecBytes.length);
    dataBytesOffset += numDataBytesInBlock[0];
  }
  if (numDataBytes != dataBytesOffset) {
    throw WriterException('Data bytes does not match offset');
  }

  final result = BitArray();

  // First, place data blocks.
  for (int i = 0; i < maxNumDataBytes; ++i) {
    for (BlockPair block in blocks) {
      final dataBytes = block.dataBytes;
      if (i < dataBytes.length) {
        result.appendBits(dataBytes[i], 8);
      }
    }
  }
  // Then, place error correction blocks.
  for (int i = 0; i < maxNumEcBytes; ++i) {
    for (BlockPair block in blocks) {
      final ecBytes = block.errorCorrectionBytes;
      if (i < ecBytes.length) {
        result.appendBits(ecBytes[i], 8);
      }
    }
  }
  if (numTotalBytes != result.sizeInBytes) {
    // Should be same.
    throw WriterException(
      'Interleaving error: $numTotalBytes and ${result.sizeInBytes} differ.',
    );
  }

  return result;
}