Int 2F Fn 4A12  - Stacker 4 Lzs Compression Interface (lzsapi)             [k]

   AX = 4A12h
   CX = 5354h ("ST")
   DX = 4143h ("AC")

Return: AX = 4F4Bh ("OK") if installed
   CX = 7374h ("st") if installed
   DX = 6163h ("ac") if installed
       ES:DI -> entry point in LZSAPI server (usually, driver
             STACKER.COM) containing far address of an actual
             LZSINFO structure (see #2494)

See Also: AX=4A12h/CX=4D52h,INT 25/AX=CDCDh

Format of LZSINFO structure:
Offset Size    Description (Table 2494)
 00h  6 BYTEs  signature "LZSAPI"
 06h   WORD    server version (200 (0C8h) for Stacker 4 and Stacker Anywhere)
 08h  4 BYTEs  vendor signature
       "STAC" = Stac Electronics, Inc.
 0Ch  6 BYTEs  ???
 12h   WORD    bit flags: server status/capabilities (see #2495)
 14h   DWORD   -> Stacker 3.X-compatible compression procedure
 18h   DWORD   -> Stacker 3.X-compatible decompression procedure
 1Ch  4 BYTEs  reserved (always set to 0)
 20h   DWORD   -> incremental Stacker 3.x-compatible compression procedure
         (see #2496)
 24h  4 BYTEs  ???
 28h   DWORD   -> incremental Stacker 3.x-compatible decompression procedure
         (see #2497)
 2Ch  4    BYTES   ???
 30h   DWORD   -> new (Stacker 4) compression procedure
 34h  4 BYTEs  ???
 38h   DWORD   -> new (Stacker 4) decompression procedure

Notes: Stacker 4 usally keeps two different data-compression algorithms in
     memory (preferably in XMA):
       1) new (Stacker 4) data compression algorithm (4K LZ77 with hashing
         and static Huffman encoding), and
       2) old (Stacker 3.x-compatible) one (2K LZ77 with hashing), which
         is used to work with STACVOL files created under older
         versions of Stacker.

Bitfields for LZSAPI capabilities:
Bit(s) Description (Table 2495)
 0 ???
 1 busy/error flag
 2-10  ???
 11    maximum compressor/decompressor presented

(Table 2496)
Call Stacker 3.x-style non-incremental functions with:
   STACK:  DWORD   return address for compress/decompress procedure
       WORD    compression algorithm parameters (see #2498)
       WORD    size of destination buffer (in bytes)
       DWORD   address of destination buffer
       WORD    size of source buffer (in bytes)
       DWORD   address of source buffer

Return: (compression/decompression procedure)
   AX = size of resulting data in destination buffer
       0000h if error (either destination buffer too small or error in
         compressed data)

(Table 2497)
Call Stacker 4-style incremental procedures with:
   STACK:  DWORD   return address for compr./decompr. procedure
       DWORD   address of LZSSWAP structure (see #2499)
           if 0000:0000, procedure uses non-incremental technique
       WORD    compression algorithm parameters (see #2498)
       WORD    size of destination buffer (in bytes)
       DWORD   address of destination buffer
       WORD    size of source buffer (in bytes)
       DWORD   address of source buffer

(Table 2498)
Values for Compression algorithm parameters:
Value  Compression level (/P=xx parameter)
 07F9h   1
 0621h   2
 0625h   3
 0665h   4
 0669h   5
 06E9h   6
 06EDh   7
 07D1h   8
 07D9h   9

Format of LZSSWAP structure:
Offset Size    Description (Table 2499)
 00h  2 BYTEs  signature "CS"
 02h  6 BYTEs  reserved
 08h   DWORD   address of destination buffer swapping procedure
 0Ch   DWORD   address of stack swapping procedure