Appendix H — The "Ad Lib Comp." format

The Ad Lib Gold software ships compressed in a proprietary container, GOLD*.CMP, expanded at install time by SETUPGLD.EXE. Because the installer gates on the physical card ("Gold Card not found") and its decompressor is bound up with the C++ runtime, recovering the installed files meant reverse-engineering the format from the 16-bit executable. This appendix documents both the container and its codec.

The container

Every stream begins with the ASCII magic Ad Lib Comp. followed by 1A 00. After the 14-byte header comes a marker stream:

Concatenating the three spanned parts and walking this stream recovers the full directory tree — 133 files across \GOLD, \GOLD\DRIVERS and \GOLD\SMP. Note the per-file header stores only the compressed size; the decoder runs until its input is exhausted.

The codec

Each file's payload is a bespoke LZ77 + static-Huffman stream (conceptually DEFLATE-like, but Ad Lib's own bit-format), decoded LSB-first:

• 3-byte prologue: mode, offset-bits (4–6), and a bit-buffer seed.

• Literal/length alphabet: a 16-entry Huffman tree selects a category; a base value plus a few extra bits give the symbol. Values < 0x100 are literal bytes; ≥ 0x100 are match lengths (length = value − 0xFE, minimum 2). The category bases and extra-bit widths are:

  category	0–7	8	9	10	11	12	13	14	15
  base	0…7	8	10	14	22	38	70	134	262
  extra bits	0	1	2	3	4	5	6	7	8

• Offsets: a 64-entry Huffman position tree, with a length-dependent number of direct bits appended (2 bits when the match length is 2, otherwise the header's offset-bits).

• Window: an 8 KB sliding window, flushed 4 KB at a time; an end symbol (0x306) terminates. In mode 0 — used by all 133 files — the Huffman tables are the fixed set above rather than being transmitted.

How it was recovered

Static analysis with capstone located the decode routines in SETUPGLD.EXE (the main LZ loop, decode_char, decode_position, the getbits bit-reader and make_table) and mapped the decoder's state structure. The tables make_table reads are addressed cs:-relative — and pinning that code-segment base was the whole puzzle: the constants only make sense at the correct segment.

The winning trick was a Kraft-equality test. A valid canonical-Huffman code-length table satisfies Σ 2^(16−len) = 65536 exactly. Scanning every plausible segment for a region where both the 16- and 64-entry length tables pass Kraft yielded exactly one candidate (segment 0x35DD) — with textbook length tables ([3,2,3,3,4,4,4,5,5,5,5,6,6,6,7,7], …). With the real tables in hand, the genuine decode routines were driven over them (via a unicorn CPU emulation, sidestepping the C++ init) and validated against the oracle: CTRLDRV.EXE, which ships uncompressed on Disk 1, decoded byte-for-byte identically. All 133 files then decoded in seconds.

This is a preservation/interoperability reverse-engineering of a 1992 format whose author released the surrounding toolkit as freeware; it exists only to recover the archived software documented in Appendix F.