Adapted from FID.C — a utility to browse Apple II .DSK image files by Paul Schlyter (pausch@saaf.se)

  S-C Assembler file format:

 <Length_of_file> (16-bit little endian)
 <Line>
 ......
 <Line>

 where <Line> is:
 <Length>     (8-bit: including length byte, line no, contents, zero>
 <Line no>    (16-bit little endian: 0-65535)
 <Characters>
 <Zero byte>  ($00, to mark the end of the S-C Asm source line)

 where <Characters> are an arbitrary sequence of:
 <Literal character>:      $20 to $7E - literal characters
 <Compressed spaces>:      $80 to $BF - represents 1 to 63 spaces
 <Compressed repetition>:  $C0 <n> <ch> - represents <ch> n times