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