mirror of
https://github.com/vxunderground/MalwareSourceCode
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454 lines
14 KiB
NASM
454 lines
14 KiB
NASM
; BROWSE.ASM -- Full Screen File Pager
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; ====================================
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CSEG Segment
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Assume CS:CSEG, DS:CSEG, ES:CSEG, SS:CSEG
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Org 0080h
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Parameter Label Byte
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Org 0100h
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Entry: Jmp Begin
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; All Data
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; --------
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db 'ATTR='
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Attribute db 0 ; Current screen attribute
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db 'SHIFT='
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ShiftHoriz db 8 ; Horizontal shift screen default
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DosVersionFail db 'Requires DOS 2.0 or above$'
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NoSpaceFail db 'Not enough memory$'
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FileFail db 'File Not Found$'
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ScreenFail db 'Unsupported video mode$'
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Delimiters db 9,' ,;=/' ; Delimiters in parameter
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FileHandle dw ? ; Use for saving file handle
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WSMode db 0FFh ; AND value for non-WordStar mode
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LineLength db ? ; Length of line (from BIOS)
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NumberLines db 25,0 ; Number of lines (check EGA BIOS)
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ScreenSize dw ? ; Size of screen in bytes
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CheckRetrace db 1 ; Flag zero if EGA or MONO used
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Addr6845 dw ? ; Could use for retrace check
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ScreenAddr Label DWord ; Address of screen
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ScreenOff dw 0 ; Higher for non-page 0
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ScreenSeg dw 0B800h ; Set to B000h for Mono Mode 7
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ScreenStart dw ? ; Points within buffer
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EndOfFile dw ? ; Points within buffer
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FileOffset dw -1, -1 ; Address within file of buffer data
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HorizOffset dw 0 ; Horizontal offset for display
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RightMargin dw 0 ; Right margin for offset display
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Dispatch dw Home, Up, PgUp, Dummy, Left
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dw Dummy, Right, Dummy, End, Down, PgDn
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; Check DOS Version for 2.0 or above
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; ----------------------------------
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Begin: Cld ; All string directions forward
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Mov AH,30h
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Int 21h ; Get DOS Version Number
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Cmp AL,2 ; Check for 2.0 or later
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Jae DOSVerOK
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Mov DX,Offset DOSVersionFail
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ErrorExit: Mov AH,9 ; Write error message
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Int 21h
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Int 20h
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; Parse Command Line to get File Name and WordStar flag
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; -----------------------------------------------------
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DOSVerOK: Mov SI,1 + Offset Parameter ; Points to parameter
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NameSearch: Lodsb ; Get byte
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Cmp AL,13 ; Check if carriage return
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Jz NoFileFound ; If so, no file name
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Mov DI,Offset Delimiters ; String of delimiters
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Mov CX,5 ; Number of delimiters (no /)
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Repne Scasb ; See if a match
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Je NameSearch ; If a delimiter, keep looking
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Mov DX,SI ; Otherwise found file name
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Dec DX ; Points to beginning of it
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EndSearch: Lodsb ; Get next byte
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Cmp AL,13 ; See if carriage return
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Je GotFileEnd ; If so, we're all done
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Mov DI,Offset Delimiters ; String of delimiters
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Mov CX,6 ; Number (including /)
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Repne Scasb ; See if a match
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Jne EndSearch ; If not, still in file name
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Mov Byte Ptr [SI - 1],0 ; If so, mark end of file name
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Jcxz GotFlag ; If slash, check for W
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Jmp EndSearch ; Or continue flag search
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GotFlag: Lodsb ; Get byte after / flag
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Or AL,20h ; Uncapitalize
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Cmp AL,'w' ; See if w for WordStar mode
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Jnz GotFileEnd ; If not, just ignore it
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Mov [WSMode],7Fh ; AND value for WordStar
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; Open the File
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; -------------
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GotFileEnd: Mov Byte Ptr [SI - 1],0 ; Mark end of file name
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; DX still points to name
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Mov AX,3D00h ; Open file for reading
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Int 21h ; by calling DOS
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Jnc GotTheFile ; If no error, continue
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NoFileFound: Mov DX,Offset FileFail ; Otherwise print a message
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Jmp ErrorExit
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GotTheFile: Mov [FileHandle],AX ; Save the file handle
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; Get Screen Mode Information from BIOS Data Area
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; -----------------------------------------------
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Push ES ; Save register
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Sub AX,AX
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Mov ES,AX ; Set ES to 0 (BIOS Data)
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Mov AL,ES:[0449h] ; Current Video Mode
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Cmp AL,3 ; Check if Color Alpha
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Jbe DisplayOK ; Continue if so
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Cmp AL,7 ; Check if monochrome display
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Je Monochrome ; If so, branch
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Mov DX,Offset ScreenFail ; We can't handle graphics
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Jmp ErrorExit ; So print an error message
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Monochrome: Mov [ScreenSeg],0B000h ; Use Monochrome Segment
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Mov [CheckRetrace],0 ; Don't have to check retrace
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DisplayOK: Mov AL,ES:[044Ah] ; Number of Columns
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Mov [LineLength],AL ; Save it
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Mov AX,ES:[044Eh] ; Offset into screen buffer
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Mov [ScreenOff],AX ; Save it
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Mov AX,ES:[0463h] ; Address of 6845 Regsiter
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Mov [Addr6845],AX ; Save it
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Push ES
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Sub DL,DL ; Set Rows to zero first
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Sub BH,BH
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Mov AX,1130h ; EGA BIOS: Get Information
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Int 10h
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Pop ES
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Or DL,DL ; Check if DL is still zero
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Jz NoEGA ; If so, skip rest of stuff
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Inc DL
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Mov [NumberLines],DL ; Save Number of Lines
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Test Byte Ptr ES:[0487h],4 ; Check if must check retrace
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Jnz NoEGA
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Mov [CheckRetrace],0 ; EGA says we don't have to
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NoEGA: Mov BH,ES:[0462h] ; Get Current Page (use later)
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Pop ES
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Mov AL,[LineLength] ; Length of each line
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Mul [NumberLines] ; Total chars on screen
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Add AX,AX ; Double for attributes
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Mov [ScreenSize],AX ; And Save it
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; See if enough memory is left
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; ----------------------------
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Add AX,Offset ScreenHold ; Add ScreenSize to code end
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Add AX,256 ; Add a little stack room
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Cmp AX,SP ; Check against stack pointer
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Jbe GotEnufMemory ; Continue if OK
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Mov DX,Offset NoSpaceFail ; Otherwise end program
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Jmp ErrorExit ; with error messae
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; Get Current Screen Attribute
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; ----------------------------
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GotEnufMemory: Cmp [Attribute],0 ; Check if attribute pre-set
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Jnz GotAttribute ; If so, move on
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Mov DL,' ' ; Write out a byte
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Mov AH,2 ; using DOS
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Int 21h
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Mov AL,8 ; Now backspace
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Mov AH,14 ; using BIOS call
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Int 10h
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Mov AH,8 ; Read character & attribute
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Int 10h ; using BIOS call (BH = pg)
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Mov [Attribute],AH ; And save attribute
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; Save Current Screen
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; -------------------
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GotAttribute: Mov DX,Offset Terminate ; Set Ctrl-Break exit
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Mov AX,2523h ; to terminate that way
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Int 21h
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Mov DI,Offset ScreenHold ; Destination of screen
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Mov CX,[ScreenSize] ; Size of screen
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Push DS ; Save Source Segment
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Lds SI,[ScreenAddr] ; Get screen address
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Rep Movsb ; Move in the bytes
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Pop DS ; Restore Source Segment
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; Get Keyboard Key and Decide on Action
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; -------------------------------------
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Call Home ; Read file in
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Mov [ScreenStart],SI ; Set buffer address
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KeyLoop: Call UpDateScreen ; Write file to screen
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GetKey: Mov AH,8 ; Get key
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Int 21h ; by calling DOS
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Cmp AL,27 ; Check if ESC
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Je Terminate ; If so, terminate
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Cmp AL,0 ; Check if extended
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Jnz GetKey ; If not, try again
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Mov AH,8 ; Get extended code
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Int 21h ; by calling DOS
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Sub AL,71 ; Subtract Home key value
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Jb GetKey ; If below that, not valid
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Cmp AL,(81 - 71) ; Check if above PgDn
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Ja GetKey ; If so, ignore it
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Sub AH,AH ; Zero out top byte
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Add AX,AX ; Double for word access
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Mov BX,AX ; Offset in dispatch table
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Mov SI,[ScreenStart] ; Set current buffer pointer
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Call [Dispatch + BX] ; Do the call
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Mov [ScreenStart],SI ; Set new buffer pointer
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Jmp KeyLoop ; And update the screen
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; Terminate -- Restore screen and close file
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; ------------------------------------------
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Terminate: Mov SI,Offset ScreenHold ; Address of Saved Screen
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Les DI,[ScreenAddr] ; Address of Display
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Mov CX,[ScreenSize] ; Number of characters
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Rep Movsb ; Move them back
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Mov BX,[FileHandle] ; Get File Handle
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Mov AH,3Eh ; Close File
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Int 21h
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Int 20h ; Terminate
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; Cursor Key Routines -- Home Key
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; -------------------------------
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Home: Sub BX,BX ; For zeroing out values
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Mov AX,[FileOffset] ; Check if read in file
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Or AX,[FileOffset + 2]
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Mov [FileOffset],BX ; Zero out file address
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Mov [FileOffset + 2],BX
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Mov [HorizOffset],BX ; Zero out horizontal offset
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Mov SI,Offset Buffer ; Reset buffer pointer
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Jz Dummy ; Skip file read if in already
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Mov DX,Offset Buffer ; Area to read file in
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Mov CX,32768 ; Number of bytes to read
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Call FileRead ; Read in file
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Dummy: Ret
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; Up and PgUp Keys
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; ----------------
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Up: Call GetPrevChar ; Get previous char in buffer
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Jc UpDone ; If none available, finish
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UpLoop: Call GetPrevChar ; Get previous char again
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Jc UpDone ; if none, we're done
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Cmp AL,10 ; Check if line feed
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Jnz UpLoop ; If not, try again
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Call GetNextChar ; Get char after line feed
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UpDone: Ret
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PgUp: Mov CX,Word Ptr [NumberLines] ; Number of lines
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PgUpLoop: Call Up ; Do UP that many times
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Loop PgUpLoop
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Ret
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; Left and Right Keys
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; -------------------
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Left: Mov [HorizOffset],0 ; Reset Horizontal Offset
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Ret
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Right: Mov AL,[ShiftHoriz] ; Get places to shift
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Sub AH,AH
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Add [HorizOffset],AX ; Move that many right
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Ret
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; End, Down, and PgDn Keys
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; ------------------------
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End: Mov BX,SI ; Save buffer pointer
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Call PgDn ; Go page down
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Cmp BX,SI ; Check if we did so
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Jnz End ; If so, do it again
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Ret
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Down: Call GetNextChar ; Get next character
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Jc NoMoreDown ; If no more, we're done
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DownLoop: Call GetNextChar ; Get one again
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Jc UpLoop ; If no more, find prev LF
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Cmp AL,10 ; See if line feed
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Jnz DownLoop ; If not, continue
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NoMoreDown: Ret
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PgDn: Mov CX,Word Ptr [NumberLines] ; Number of lines
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PgDnLoop: Call Down ; Do DOWN that many times
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Loop PgDnLoop
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Ret
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; Update Screen
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; -------------
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UpdateScreen: Push ES
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Mov SI,[ScreenStart] ; Address of data in buffer
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Les DI,[ScreenAddr] ; Address of display
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Mov CX,ScreenSize ; Number of bytes in screen
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Shr CX,1 ; Half for number of chars
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Mov AL,' ' ; Will blank screen
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Mov AH,[Attribute] ; With screen attribute
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Rep Stosw ; Blank it
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Mov AL,[LineLength] ; Length of display line
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Sub AH,AH
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Add AX,[HorizOffset] ; Add Horizontal Offset
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Mov [RightMargin],AX ; That's right display margin
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Sub DL,DL ; Line Number
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LineLoop: Sub BX,BX ; Column Number
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Mov AL,[LineLength] ; Use Line Length
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Mul DL ; and Line Number
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Add AX,AX ; to recalculate
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Mov DI,AX ; display destination
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Add DI,[ScreenOff] ; Add beginning address
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CharLoop: Call GetNextChar ; Get next character
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Jc EndOfScreen ; If no more, we're done
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And AL,[WSMode] ; Will be 7Fh for WordStar
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Cmp AL,13 ; Check for carriage return
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Je CharLoop ; Do nothing if so
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Cmp AL,10 ; Check for line feed
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Je LineFeed ; Do routine if so
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Cmp AL,9 ; Check for tab
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Je Tab ; Do routine if so
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Mov CX,1 ; Just 1 char to display
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PrintChar: Cmp BX,[HorizOffset] ; See if we can print it
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Jb NoPrint
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Cmp BX,[RightMargin] ; See if within margin
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Jae NoPrint
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Mov AH,[Attribute] ; Attribute for display
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Cmp [CheckRetrace],0 ; See if must stop snow
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Jz WriteIt ; If not, skip retrace wait
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Push BX
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Push DX
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Mov BX,AX ; Save character and attribute
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Mov DX,[Addr6845] ; Set up I/O address
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Add DX,6
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RetraceWait1: In AL,DX ; Check until
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Shr AL,1 ; vertical retrace
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Jc RetraceWait1 ; ends
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Cli ; Clear interrupts
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RetraceWait2: In AL,DX ; Check until
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Shr AL,1 ; vertical retrace
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Jnc RetraceWait2 ; begins
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Mov AX,BX ; Get back character & attr
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Stosw ; Write to display
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Sti ; Enable interrupts again
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Pop DX
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Pop BX
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Jmp Short NoPrint ; Skip around "no snow" write
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WriteIt: Stosw ; Write without retrace wait
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NoPrint: Inc BX ; Bump up line counter
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Loop PrintChar ; Do it CX times
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Jmp CharLoop ; Then go back to top
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Tab: Mov AX,BX ; Current column number
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And AX,07h ; Take lower three bits
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Mov CX,8
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Sub CX,AX ; Subtract from 8
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Mov AL,' ' ; Will print CX blanks
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Jmp PrintChar
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LineFeed: Inc DL ; Next line
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Cmp DL,[NumberLines] ; See if down at bottom
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Jb LineLoop ; If not, continue
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EndOfScreen: Pop ES ; All done -- leave
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Ret
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; Get Next Character from buffer
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; ------------------------------
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; (Input is SI pointing to buffer, Returns AL, CY if no more)
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GetNextChar: Cmp SI,[EndOfFile] ; See if at end of file
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Jae NoMoreNext ; If so, no more chars
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Cmp SI,Offset BufferEnd ; See if at end of buffer
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Jb CanGetNext ; If not, just get character
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Push CX ; Otherwise save registers
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Push DX
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Push DI
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Push ES
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Push DS ; Set ES to DS
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Pop ES ; (could be different)
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Mov SI,Offset BufferMid ; Move 2nd buffer half
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Mov DI,Offset Buffer ; to 1st buffer half
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Mov CX,16384
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Sub [ScreenStart],CX ; New buffer pointer
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Rep Movsb ; Move them
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Mov SI,DI ; SI also buffer pointer
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Add [FileOffset],32768 ; Adjust file addr to read
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Adc [FileOffset + 2],0
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Mov DX,Offset BufferMid ; Place to read file
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Mov CX,16384 ; Number of bytes
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Call FileRead ; Read the file
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Sub [FileOffset],16384 ; Now adjust so reflects
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Sbb [FileOffset + 2],0 ; 1st half of buffer
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Pop ES ; Get back registers
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Pop DI
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Pop DX
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Pop CX
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Jmp GetNextChar ; And try again to get char
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CanGetNext: Lodsb ; Get the character
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NoMoreNext: Cmc ; So CY set if no more
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Ret
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; Get Previous Character from buffer
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; ----------------------------------
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GetPrevChar: Cmp SI,Offset Buffer ; See if at top of buffer
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Ja CanGetPrev ; If not, just get character
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Mov AX,[FileOffset] ; See if at top of file
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Or AX,[FileOffset + 2]
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Jz AtTopAlready ; If so, can't get anymore
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Push CX ; Save some registers
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Push DX
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Mov SI,Offset Buffer ; Move 1st half of buffer
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Mov DI,Offset BufferMid ; to 2nd half of buffer
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Mov CX,16384
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Add [ScreenStart],CX ; New buffer pointer
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Rep Movsb ; Do the move
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Sub [FileOffset],16384 ; Adjust file addr for read
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Sbb [FileOffset + 2],0
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Mov DX,Offset Buffer ; Area to read file into
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Mov CX,16384 ; Number of bytes
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Call FileRead ; Read the file
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Pop DX ; Get back registers
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Pop CX
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Jmp Short CanGetPrev ; Now get character
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AtTopAlready: Stc ; CY flag set for no more
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Ret
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CanGetPrev: Dec SI ; Move pointer back
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Mov AL,[SI] ; Get the character
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Clc ; CY flag reset for success
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Ret
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; Read CX bytes from the file into DX buffer
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; ------------------------------------------
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FileRead: Push AX ; Save some registers
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Push BX
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Push CX
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Push DX
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Mov [EndOfFile],-1 ; Initialize this
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Mov DX,[FileOffset] ; Get file address to read
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Mov CX,[FileOffset + 2]
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Mov BX,[FileHandle] ; Get file Handle
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Sub AL,AL ; Do LSEEK from beginning
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Mov AH,42h ; LSEEK call
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Int 21h
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Pop DX ; Get back destination
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Pop CX ; Get back count
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Mov AH,3Fh ; Read file function call
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Int 21h
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Jnc NoReadError ; If no error, continue
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Sub AX,AX ; Otherwise read zero bytes
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NoReadError: Cmp AX,CX ; See if 32K has been read
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Je GotItAll ; If so, we're home free
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Add AX,DX ; Otherwise add to buffer addr
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Mov [EndOfFile],AX ; And save as end of file
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GotItAll: Pop BX
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Pop AX
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Ret
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; File Buffer and Screen Hold Areas
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; ---------------------------------
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Buffer Label Byte ; Area for file reads
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BufferMid equ Buffer + 16384 ; Halfway through it
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BufferEnd equ BufferMid + 16384 ; At end of it
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ScreenHold equ BufferEnd ; Area for holding screen
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CSEG EndS ; End of segment
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End Entry ; Denotes entry point
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