Int 2F/AX=4A12h/CX=5354h

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Stacker 4 LZS Compression Interface (LZSAPI)

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 #02808)

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

Format of LZSINFO structure: Offset Size Description (Table 02808) 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 #02809) 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 #02810) 24h 4 BYTEs ??? 28h DWORD -> incremental Stacker 3.x-compatible decompression procedure (see #02811) 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 02809) 0 ??? 1 busy/error flag 2-10 ??? 11 maximum compressor/decompressor presented

(Table 02810) Call Stacker 3.x-style non-incremental functions with:.

STACK:
DWORD return address for compress/decompress procedure WORD compression algorithm parameters (see #02812) 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 02811) Call Stacker 4-style incremental procedures with:.

STACK:
DWORD return address for compr./decompr. procedure DWORD address of LZSSWAP structure (see #02813) if 0000:0000, procedure uses non-incremental technique WORD compression algorithm parameters (see #02812) 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 02812) 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 02813) 00h 2 BYTEs signature "CS" 02h 6 BYTEs reserved 08h DWORD address of destination buffer swapping procedure 0Ch DWORD address of stack swapping procedure

Category: File/Disk Compression - Int 2Fh - S

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