Int 1A Fn B001  - Microsoft Real-time Compression Interface (mrci) - Rom-  [d]

   AX = B001h
   CX = 4D52h ("MR")
   DX = 4349h ("CI")

Return: CX = 4943h ("IC") if installed
   DX = 524Dh ("RM") if installed
       ES:DI -> MRCINFO structure (see #0649)

Note:  this call is functionally identical to INT 2F/AX=4A12h, which should
     be called first, as this call is used for the first, ROM-based
     MRCI server, while the other call is used for RAM-based servers
     which may be partially or entirely replacing a prior server

See Also: INT 2F/AX=4A12h

Format of MRCINFO structure:
Offset Size    Description (Table 0649)
 00h  4 BYTEs  vendor signature
       "MSFT" Microsoft
 04h   WORD    server version (high=major)
 06h   WORD    MRCI specification version
 08h   DWORD   address of server entry point (see #0651)
 0Ch   WORD    bit flags: server capabilities (see #0650)
 0Eh   WORD    bit flags: hardware assisted capabilities (see #0650)
 10h   WORD    maximum block size supported by server (at least 8192 bytes)

Bitfields for MRCI capabilities:
Bit(s) Description (Table 0650)
 0 standard compress
 1 standard decompress
 2 update compress
 3 MaxCompress (not present in initial public release)
 4 reserved
 5 incremental decompress
 6 MRCI 2.0 standard compress
 7 MRCI 2.0 standard decompress
 8-14  reserved
 15    this structure is in ROM and can't be modified
   (server capabilities only)

(Table 0651)
Call MRCI entry point with:
   DS:SI -> MRCREQUEST structure (see #0652)
   CX = type of client (0000h application, 0001h file system)
   AX = operation
       0001h perform standard compression
       0002h perform standard decompression
       0004h perform update compression
       0008h perform MaxCompress
       0020h perform incremental decompression
       0040h perform MRCI 2.0 standard compression
       0080h perform MRCI 2.0 standard decompression
   AX = FFFFh clear flags
       BX = bitmask of flags to clear (set bits in BX are flags to clear)

Return: AX = status
       0000h successful
       0001h invalid function
       0002h server busy, try again
       0003h destination buffer too small
       0004h incompressible data
       0005h bad compressed data format
   BP destroyed (MS-DOS 6.2)

Note:  MRCI driver may chain to a previous driver

Format of MRCREQUEST structure:
Offset Size    Description (Table 0652)
 00h   DWORD   pointer to source buffer
 04h   WORD    size of source buffer (0000h = 64K)
 06h   WORD    (UpdateCompress only)
       (call) offset in source buffer of beginning of changed data
       (ret) offset in destination buffer of beginning of changed
             compressed data
 08h   DWORD   pointer to destination buffer
       must contain original compressed data for UpdateCompress
 0Ch   WORD    size of destination buffer (0000h = 64K)
       any compression: size of buffer for compressed data
       standard decompression: number of bytes to be decompressed
       incremental decompression: number of byte to decompress now
       (ret) actual size of resulting data
 0Eh   WORD    client compressed data storage allocation size
 10h   DWORD   incremental decompression state data
       set to 00000000h before first incremental decompression call

Notes: the source and destination buffers may not overlap
   the source and destination buffer sizes should normally be the same
   application should not update the contents of the MRCREQUEST structure
     between incremental decompression calls