title: NSData & NSMutabledata. How do I read from within the body of a data object?
body: <p>I have a lllooonnnggg NSMutableData instance. I want to feed non-overlapping sub-ranges this data to other objects. I've perused the NSData/NSMutableData docs and don't quite have a grasp of the proper way to do this.</p>
  
  <p>So for example the NSMutableData replaceBytesInRange:withBytes: looks ideal but I need the withBytes: parameter to point to a location beyond the head of the byte stream returned by  [mySourceHumungousData bytes].</p>
  
  <p>I can get hack-ish and drop into pure C and do this but I'd prefer not to do that.</p>
  
  <p>Cheers,
  Doug</p>