getNumDataBytesAndNumECBytesForBlockID static method

void getNumDataBytesAndNumECBytesForBlockID(int numTotalBytes, int numDataBytes, int numRSBlocks, int blockID, Int32List numDataBytesInBlock, Int32List numECBytesInBlock,)

Get number of data bytes and number of error correction bytes for block id "blockID". Store the result in "numDataBytesInBlock", and "numECBytesInBlock". See table 12 in 8.5.1 of JISX0510:2004 (p.30)

Implementation

static void getNumDataBytesAndNumECBytesForBlockID(
    int numTotalBytes,
    int numDataBytes,
    int numRSBlocks,
    int blockID,
    Int32List numDataBytesInBlock,
    Int32List numECBytesInBlock) {
  if (blockID >= numRSBlocks) {
    throw WriterException('Block ID too large');
  }
  // numRsBlocksInGroup2 = 196 % 5 = 1
  var numRsBlocksInGroup2 = numTotalBytes % numRSBlocks;
  // numRsBlocksInGroup1 = 5 - 1 = 4
  var numRsBlocksInGroup1 = numRSBlocks - numRsBlocksInGroup2;
  // numTotalBytesInGroup1 = 196 / 5 = 39
  var numTotalBytesInGroup1 = numTotalBytes ~/ numRSBlocks;
  // numTotalBytesInGroup2 = 39 + 1 = 40
  var numTotalBytesInGroup2 = numTotalBytesInGroup1 + 1;
  // numDataBytesInGroup1 = 66 / 5 = 13
  var numDataBytesInGroup1 = numDataBytes ~/ numRSBlocks;
  // numDataBytesInGroup2 = 13 + 1 = 14
  var numDataBytesInGroup2 = numDataBytesInGroup1 + 1;
  // numEcBytesInGroup1 = 39 - 13 = 26
  var numEcBytesInGroup1 = numTotalBytesInGroup1 - numDataBytesInGroup1;
  // numEcBytesInGroup2 = 40 - 14 = 26
  var numEcBytesInGroup2 = numTotalBytesInGroup2 - numDataBytesInGroup2;
  // Sanity checks.
  // 26 = 26
  if (numEcBytesInGroup1 != numEcBytesInGroup2) {
    throw WriterException('EC bytes mismatch');
  }
  // 5 = 4 + 1.
  if (numRSBlocks != numRsBlocksInGroup1 + numRsBlocksInGroup2) {
    throw WriterException('RS blocks mismatch');
  }
  // 196 = (13 + 26) * 4 + (14 + 26) * 1
  if (numTotalBytes !=
      ((numDataBytesInGroup1 + numEcBytesInGroup1) * numRsBlocksInGroup1) +
          ((numDataBytesInGroup2 + numEcBytesInGroup2) *
              numRsBlocksInGroup2)) {
    throw WriterException('Total bytes mismatch');
  }

  if (blockID < numRsBlocksInGroup1) {
    numDataBytesInBlock[0] = numDataBytesInGroup1;
    numECBytesInBlock[0] = numEcBytesInGroup1;
  } else {
    numDataBytesInBlock[0] = numDataBytesInGroup2;
    numECBytesInBlock[0] = numEcBytesInGroup2;
  }
}