code: @Override public long getLength() {
  		final long vsHi   = vStart & ~0xffff;
  		final long veHi   = vEnd   & ~0xffff;
  		final long hiDiff = veHi - vsHi;
  		return hiDiff == 0 ? ((vEnd & 0xffff) - (vStart & 0xffff)) : hiDiff;
  	}
docs: Inexact due to the nature of virtual offsets.
  
  We can't know how many blocks there are in between two file offsets, nor
  how large those blocks are. So this uses only the difference between the
  file offsets—unless that difference is zero, in which case the split is
  wholly contained in one block and thus we can give an exact result.