Here are some notes on building programs that write IFF files, which is much easier than reading them. o An IFF file is a single FORM, LIST, or CAT chunk. o Any IFF-85 file must start with the 4 characters "FORM", "LIST", or "CAT ", followed by a LONG ckSize. There should be no data after the chunk end. o Chunk types LIST, FORM, PROP, and CAT are generic. They always contain a subtype ID followed by chunks. These three IDs are universally reserved, as are "LIS1" through "LIS9", "FOR1" through "FOR9", "CAT1" through "CAT9", and " ". o Don't forget to write a 0 pad byte after each odd-length chunk. o Do not try to edit a file that you don't know how to create. Programs may look into a file and copy out nested FORMs of types that they recognize, but they should not edit and replace the nested FORMs and not add or remove them. Breaking these rules could make the containing structure inconsistent. You may write a new file containing items you copied, or copied and modified, but don't copy structural parts you don't understand. o You must adhere to the syntax descriptions in Appendix A. E.g., PROPs may only appear inside LISTs. There are at least four common techniques for writing an IFF group: (1) build the data in a file mapped into virtual memory. (2) build the data in memory blocks and use block I/O. (3) stream write the data piecemeal and (don't forget!) random access back to set the group (or FORM) length count. (4) make a preliminary pass to compute the length count then stream write the data. Issue: The standard disallows "blind" chunk copying for consistency reasons. Perhaps we can define a ckID convention for chunks that are OK to replicate without knowledge of the contents. Any such chunks would need to be internally consistent, and not be bothered by changed external references. Issue: Stream-writing an IFF FORM can be inconvenient. With random access files one can write all the chunks then go back to fix up the FORM size. With stream access, the FORM size must be calculated before the file is written. When compression is involved, this can be slow or inconvenient. Perhaps we can define an "END " chunk. The stream writer would use -1 ($FFFFFFFF) as the FORM size. The reader would follow each chunk, when the reader reaches an "END ", it would terminate the last -1 sized chunk. Certain new IFF FORMs could require that readers understand "END ".
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