General File Structure and Block Structure

General File Structure

0x0000 Header
0x0800 Top Level Index Block
0x0C00 Fist Data Level Block
...    Any further block in random order

Block Structure

A block is 0x400 bytes of data, containing up to 0x3F2 bytes of payload. A block has the following structure:

• <DELETED FLAG> byte
  has the value of 0xFF if the block is deleted
• <INDEX LEVEL> byte
  the index level is 0 for data blocks. Otherwise it is the hierarchy number of the index.
• <PREV ID> word
  the id of the block preceding this block in the data stream
• <NEXT ID> word
  the id of the block following this block in the data stream
• <SKIP BYTES> halfword
  the number of bytes that are identical to the parsing state relative to the previous block – these bytes can be skipped if the parser continues parsing the data stream
• <PAYLOAD LENGTH> halfword
• <PAYLOAD> <PAYLOAD LENGTH> bytes
• <PADDING> 0x3F2 - <PAYLOAD LENGTH> bytes

e.g. the block header 00 00 00017D27 00017D28 0003 0111 would tell us

• it is not deleted
• it is a data block
• the previous block id is 0x00017D27
• the next block id is 0x00017D28
• 3 can be skipped if this block is not the entry point for the parser
• the payload is 0x111 bytes long

Points of interest

the ID for the block itself has to be derived from the context