318 lines
9.1 KiB
NASM
318 lines
9.1 KiB
NASM
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IFDEF DBLSPACE_LEGAL
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page ,130
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title DeCompressor
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;-----------------------------------------------------------------------
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; Name: RDCOMP.ASM
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;
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; Routines defined:
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; Decompress32
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;
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; Description:
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; This file holds the code that is responsible for decompressing
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; the compressed data.
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;
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; VxD History:
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; 22-Apr-93 jeffpar Major adaptation and cleanup for MRCI32.386
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;-----------------------------------------------------------------------
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.386p
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.xlist
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;; include vmm.inc
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;; include debug.inc
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include mdequ.inc
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.list
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MD_STAMP equ "SD"
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;;;-----------------------------------------------------------------------
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;;; Data segment
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;;;-----------------------------------------------------------------------
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;;
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;;VxD_LOCKED_DATA_SEG
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;;
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;; public pLowerBound
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;;pLowerBound dd 0 ; if non-zero, then this is the lowest linear
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;; ; address we treat as *our* error
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;; public pUpperBound
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;;pUpperBound dd 0 ; if non-zero, then this is the highest linear
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;; ; address we treat as *our* error (plus one)
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;; public pPrevPgFltHdlr
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;;pPrevPgFltHdlr dd 0 ; if non-zero, addr of previous page fault hdlr
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;;
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;;VxD_LOCKED_DATA_ENDS
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;;
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;;
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;;VxD_PAGEABLE_DATA_SEG
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_DATA SEGMENT DWORD PUBLIC 'DATA'
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include decode.inc ; include macros and tables used for decoding
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public decode_data_end
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decode_data_end label byte
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;;VxD_PAGEABLE_DATA_ENDS
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_DATA ENDS
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;-----------------------------------------------------------------------
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; Code segment
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;-----------------------------------------------------------------------
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;;VxD_PAGEABLE_CODE_SEG
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_TEXT SEGMENT DWORD USE32 PUBLIC 'CODE'
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ASSUME CS:FLAT, DS:FLAT, ES:FLAT, SS:NOTHING, FS:NOTHING, GS:NOTHING
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public aCmdAt
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aCmdAt dd CmdAt0,CmdAt1,CmdAt2,CmdAt3,CmdAt4,CmdAt5,CmdAt6,CmdAt7
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;-----------------------------------------------------------------------
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; Decompression Algorithm
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; -----------------------
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; Decode the next chunk of text in 'coding_buffer', into the buffer as
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; stated in the 'init'.
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;
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; Entry:
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; CLD
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; EBX == start of cluster (see MRCI32IncDecompress!)
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; ECX == chunk count
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; ESI -> compressed data
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; EDI -> destination buffer
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; EDX == remaining data(low)/bits(high) from last call, 0 if none
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;
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; Exit:
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; If successful, CY clear and:
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; ESI == offset to next byte uncompressed data (if any)
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; EDI == offset to next free byte in dest buffer
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; EDX == remaining data(low)/bits(high) for next call, 0 if none
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;
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; Uses:
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; Everything except EBP
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;-----------------------------------------------------------------------
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;;BeginProc Decompress32
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public Decompress32
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Decompress32 proc near
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push ebp
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push ebp ; [esp] is our "chunk_count"
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;; push ebx
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sub ebx,MAX_12BIT_OFFSET ;
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;; mov [pLowerBound],ebx ;
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;; pop [pUpperBound] ; fault handler enabled *now*
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mov eax,edx ; remaining data to AX
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shr edx,16 ; move state to low word of EDX
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jnz short @F ; jump if continuing previous state
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lodsw ; new decompression, load initial data
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@@: mov [esp],ecx ; save chunk count
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DecodeLoop:
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;
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; AX has the remaining bits, DL has the next state
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;
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mov ebp,cbCHUNK ; (ebp) is # bytes left this chunk
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DecodeRestart
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LastErrSJump equ <FirstErrSJump>
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FirstErrSJump: jmp DecodeError ; put first nice fat jump out of the way
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irpc c,<01234567>
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CmdAt c
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endm
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jmp CmdAt0
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irpc c,<01234567>
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LengthAt c
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endm
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DoGeneralLength ; generate code here to handle large lengths
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DecodeDone:
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;
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; AX has the remaining bits, DL has the next state -- check chunk status
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;
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test ebp,ebp ; perfect chunk-size decompression?
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jnz DecodeCheckLast ; no, check for last chunk
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dec dword ptr [esp] ; chunks remaining?
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jz DecodeSuccess ; no, so we're all done
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jmp DecodeLoop ; yes, process them
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public DecodeError
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DecodeError label near
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stc ; random decomp failure jump target
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jmp short DecodeExit
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DecodeCheckLast:
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dec dword ptr [esp] ; chunks remaining?
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jnz DecodeError ; yes, then we have an error
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DecodeSuccess:
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mov dh,1 ; return non-0 EDX indicating state exists
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shl edx,16 ; move state to high word of EDX
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movzx eax,ax ; make sure high word of EAX is clear
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or edx,eax ; EDX == state (and carry is CLEAR)
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DecodeExit:
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;; mov [pUpperBound],0 ; fault handler disabled *now*
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;; mov [pLowerBound],0 ;
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pop ebp ; throw away our "chunk_count" at [esp]
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pop ebp
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ret
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;;EndProc Decompress32
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Decompress32 endp
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;;VxD_PAGEABLE_CODE_ENDS
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_TEXT ENDS
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;;
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;;VxD_LOCKED_CODE_SEG
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;;
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;;;-----------------------------------------------------------------------
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;;; Decompress32_Page_Fault
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;;; -----------------------
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;;; Looks for VMM page faults caused by the decompressor. The fault
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;;; must have taken place in the range from [pLowerBound] to [pUpperBound]-1.
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;;; If the fault IS in that range, then we set EIP to DecodeError.
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;;;
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;;; WARNING: this takes advantage of the fact that the decompressor does not
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;;; use the stack; otherwise, we would obviously need to record and re-set ESP
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;;; to a known point as well.
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;;;
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;;; This is in locked code to insure that a subsequent fault doesn't destroy
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;;; the information necessary to process the first (eg, CR2)!
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;;;
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;;; Entry:
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;;; EBX == VM handle
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;;; EBP -> VMM re-entrant stack frame
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;;;
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;;; Uses:
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;;; May use everything except SEG REGS
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;;;-----------------------------------------------------------------------
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;;
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;;BeginProc Decompress32_Page_Fault
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;;;
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;;; Note: the fall-through case is the common one (ie, not our page fault)
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;;;
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;; push eax
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;; mov eax,cr2 ; get faulting address
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;; cmp eax,[pUpperBound]
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;; jb short dpf_maybe ; it might be ours
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;; ; otherwise, definitely not
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;;dpf_prev:
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;; pop eax ; we've been told to preserve everything
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;; jmp [pPrevPgFltHdlr] ; dispatch to real page fault handler
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;; ; (if we installed, then there *is* one)
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;;dpf_maybe:
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;; cmp eax,[pLowerBound]
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;; jb short dpf_prev ; not going to "fix" it
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;;
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;; Trace_Out "Decompress32_Page_Fault: correcting fault on bad cluster"
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;;
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;; mov [ebp].Client_EIP,OFFSET32 DecodeError
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;; pop eax
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;; ret ; we "fixed" it
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;;
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;;EndProc Decompress32_Page_Fault
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;;
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;;VxD_LOCKED_CODE_ENDS
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;++
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;
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; ULONG
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; DblsMrcfDecompress (
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; PUCHAR UncompressedBuffer,
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; ULONG UncompressedLength,
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; PUCHAR CompressedBuffer,
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; ULONG CompressedLength,
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; PMRCF_DECOMPRESS WorkSpace
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; )
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;
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; Routine Description:
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;
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; This routine decompresses a buffer of StandardCompressed or MaxCompressed
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; data.
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;
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; Arguments:
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;
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; UncompressedBuffer - buffer to receive uncompressed data
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;
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; UncompressedLength - length of UncompressedBuffer
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;
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; NOTE: UncompressedLength must be the EXACT length of the uncompressed
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; data, as Decompress uses this information to detect
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; when decompression is complete. If this value is
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; incorrect, Decompress may crash!
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;
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; CompressedBuffer - buffer containing compressed data
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;
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; CompressedLength - length of CompressedBuffer
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;
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; WorkSpace - pointer to a private work area for use by this operation
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;
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; Return Value:
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;
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; ULONG - Returns the size of the decompressed data in bytes. Returns 0 if
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; there was an error in the decompress.
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;--
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_TEXT SEGMENT DWORD USE32 PUBLIC 'CODE'
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ASSUME CS:FLAT, DS:FLAT, ES:FLAT, SS:NOTHING, FS:NOTHING, GS:NOTHING
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public _DblsMrcfDecompress@20
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_DblsMrcfDecompress@20 proc near
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push esi
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push edi
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push ebx
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mov ecx,dword ptr [esp+20]
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mov edx,ecx
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shr ecx,9
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and edx,512-1
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jz @f
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inc ecx
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sub edx,edx
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@@: mov esi,dword ptr [esp+24]
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mov edi,dword ptr [esp+16]
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mov ebx,edi
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cld
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lodsd
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cmp ax,MD_STAMP
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je @f
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sub eax,eax
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jz done
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@@: call Decompress32
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jnc @f
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sub eax,eax
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jz done
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@@: sub edi,dword ptr [esp+16]
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mov eax,edi
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done:
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pop ebx
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pop edi
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pop esi
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ret 20
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_DblsMrcfDecompress@20 endp
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_TEXT ENDS
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ENDIF ; DEF DBLSPACE_LEGAL
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end
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