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https://github.com/vxunderground/MalwareSourceCode
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404 lines
11 KiB
NASM
404 lines
11 KiB
NASM
; DOS-EDIT.ASM -- Resident DOS Command Line Editor
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; ================================================
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CSEG Segment
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Assume CS:CSEG
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Org 0080h
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KeyboardBuffer Label Byte
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Org 0100h
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Entry: Jmp Initialize
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; All Data
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; --------
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db "(C) Copyright 1985 Ziff-Davis Publishing Co."
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OldInterrupt21 dd ? ; Original Interrupt 21 vector
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OldInterrupt16 dd ? ; Original Interrupt 16 vector
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DoingBuffKey db 0 ; Flag for doing Function Call 0Ah
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BufferPointer dw KeyboardBuffer ; Pointer to Keyboard Buffer
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BufferCounter db 0 ; Number of characters in buffer
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MaxCharCol db ? ; Maximum Character Column on screen
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OriginalCursor dw ? ; Place to save cursor on full-screen
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InsertOn db 0 ; Insert mode flag
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KeyRoutine dw Home,Up,PgUp,Dummy,Left,Dummy,Right
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dw Dummy,End,Down,PgDn,Insert,Delete
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; New Interrupt 21 (DOS Function Calls)
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; -------------------------------------
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NewInterrupt21 Proc Far
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Mov CS:[DoingBuffKey],0 ; Turn flag off initially
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Cmp AH,0Ah ; Check if doing buffered input
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Jz BufferedInput
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Jmp CS:[OldInterrupt21] ; If not, do regular interrupt
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BufferedInput: Mov CS:[DoingBuffKey],-1 ; If so, turn on flag
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PushF ; Simulate regular interrupt
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Call CS:[OldInterrupt21]
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Mov CS:[DoingBuffKey],0 ; Turn off flag
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Mov CS:[BufferCounter],0 ; Re-set character counter
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IRet ; Return to user program
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NewInterrupt21 EndP
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; New Interrupt 16 (BIOS Keyboard Routine)
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; ----------------------------------------
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NewInterrupt16 Proc Far
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Sti ; Re-enable interrupts
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Cmp CS:[DoingBuffKey],0 ; Check if doing call 0Ah
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Jz DoNotIntercept ; If not, do old interrupt
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Cmp CS:[BufferCounter],0 ; Check if chars in buffer
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Jnz Substitute ; If so, get them out
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Cmp AH,0 ; See if doing a get key
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Jz CheckTheKey ; If so, get the key
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DoNotIntercept: Jmp CS:[OldInterrupt16] ; Otherwise, do old interrupt
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CheckTheKey: PushF ; Save flags
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Call CS:[OldInterrupt16] ; Do regular interrupt
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Cmp AX,4800h ; Check if up cursor
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Jnz NotTriggerKey ; If not, don't bother
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Call FullScreen ; Move around the screen
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Cmp CS:[BufferCounter],0 ; Any chars to deliver?
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Jz CheckTheKey ; If not, get another key
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ReturnBuffer: Call GetBufferChar ; Otherwise, pull one out
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Inc CS:[BufferPointer] ; Kick up the pointer
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Dec CS:[BufferCounter] ; And knock down the counter
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NotTriggerKey: IRet ; And go back to calling prog
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; Substitute Key from Buffer
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; --------------------------
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Substitute: Cmp AH,2 ; See if shift status check
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Jae DoNotIntercept ; If so, can't be bothered
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Cmp AH,0 ; See if get a key
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Jz ReturnBuffer ; If so, get the key above
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Call GetBufferChar ; Otherwise get a key
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Cmp CS:[BufferCounter],0 ; And clear zero flag
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Ret 2 ; Return with existing flags
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NewInterrupt16 EndP
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; Get Buffer Character
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; --------------------
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GetBufferChar: Push BX
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Mov BX,CS:[BufferPointer] ; Get pointer to key buffer
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Mov AL,CS:[BX] ; Get the key
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Sub AH,AH ; Blank out scan code
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Pop BX
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Ret
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; Full Screen Routine
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; -------------------
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FullScreen: Push AX ; Save all these registers
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Push BX
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Push CX
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Push DX
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Push DI
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Push DS
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Push ES
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Mov AX,CS ; Set AX to this segment
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Mov DS,AX ; Do DS is this segment
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Mov ES,AX ; And ES is also
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Assume DS:CSEG, ES:CSEG ; Tell the assembler
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Mov AH,0Fh ; Get Video State
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Int 10h ; through BIOS
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Dec AH ; Number of columns on screen
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Mov [MaxCharCol],AH ; Save maximum column
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; BH = Page Number throughout
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Mov AH,03h ; Get cursor in DX
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Int 10h ; through BIOS
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Mov [OriginalCursor],DX ; And save the cursor position
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Call Up ; Move cursor up
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MainLoop: Cmp DH,Byte Ptr [OriginalCursor + 1] ; If at line
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Jz TermFullScreen ; stated from, terminate
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Mov AH,02h ; Set cursor from DX
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Int 10h ; through BIOS
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GetKeyboard: Mov AH,0 ; Get the next key
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PushF ; By simulating Interrupt 16h
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Call CS:[OldInterrupt16] ; which goes to BIOS
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Cmp AL,1Bh ; See if Escape key
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Jz TermFullScreen ; If so, terminate full screen
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; Back Space
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; ----------
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Cmp AL,08h ; See if back space
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Jnz NotBackSpace ; If not, continue test
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Or DL,DL ; Check if cursor at left
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Jz MainLoop ; If so, do nothing
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Dec DL ; Otherwise, move cursor back
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Call ShiftLeft ; And shift line to the left
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Jmp MainLoop ; And continue for next key
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; Carriage Return
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; ---------------
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NotBackSpace: Cmp AL,0Dh ; See if Carriage Return
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Jnz NotCarrRet ; If not, continue test
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Call End ; Move line into buffer
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Mov AL,0Dh ; Tack on a Carriage Return
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Stosb ; By writing to buffer
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Inc [BufferCounter] ; One more character in buffer
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Jmp MainLoop ; And continue
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; Normal Character
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; ----------------
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NotCarrRet: Cmp AL,' ' ; See if normal character
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Jb NotNormalChar ; If not, continue test
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Cmp [InsertOn],0 ; Check for Insert mode
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Jz OverWrite ; If not, overwrite
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Call ShiftRight ; Shift line right for insert
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Jmp Short NormalCharEnd ; And get ready to print
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OverWrite: Mov CX,1 ; Write one character
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Mov AH,0Ah ; By calling BIOS
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Int 10h
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NormalCharEnd: Call Right ; Cursor to right and print
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Jmp MainLoop ; Back for another key
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; Cursor Key, Insert, or Delete Subroutine
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; ----------------------------------------
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NotNormalChar: Xchg AL,AH ; Put extended code in AL
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Sub AX,71 ; See if it's a cursor key
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Jc GetKeyboard ; If not, no good
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Cmp AX,12 ; Another check for cursor
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Ja GetKeyboard ; If not, skip it
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Add AX,AX ; Double for index
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Mov DI,AX ; into vector table
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Call [KeyRoutine + DI] ; Do the routine
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Jmp MainLoop ; Back for another key
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; Terminate Full Screen Movement
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; ------------------------------
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TermFullScreen: Mov DX,[OriginalCursor] ; Set cursor to original
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Mov AH,2 ; And set it
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Int 10h ; through BIOS
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Pop ES ; Restore all registers
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Pop DS
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Pop DI
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Pop DX
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Pop CX
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Pop BX
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Pop AX
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Ret ; And return to New Int. 16h
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; Cursor Movement
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; ---------------
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Home: Mov DL,Byte Ptr [OriginalCursor] ; Move cursor to
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Ret ; to original column
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Up: Or DH,DH ; Check if at top row
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Jz UpEnd ; If so, do nothing
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Dec DH ; If not, decrement row
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UpEnd: Ret
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PgUp: Sub DL,DL ; Move cursor to far left
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Ret
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Left: Or DL,DL ; Check if cursor at far left
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Jnz GoWest ; If not, move it left
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Mov DL,[MaxCharCol] ; Move cursor to right
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Jmp Up ; And go up one line
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GoWest: Dec DL ; Otherwise, decrement column
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Ret
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Right: Cmp DL,[MaxCharCol] ; Check if cursor at far right
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Jb GoEast ; If not, move it right
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Sub DL,DL ; Set cursor to left of screen
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Jmp Down ; And go down one line
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GoEast: Inc DL ; Otherwise, increment column
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Ret
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End: Call TransferLine ; Move line to buffer
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Mov DX,[OriginalCursor] ; Set cursor to original
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Ret
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Down: Inc DH ; Move cursor down one row
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Ret
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PgDn: Mov CL,[MaxCharCol] ; Get last column on screen
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Inc CL ; Kick it up by one
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Sub CL,DL ; Subtract current column
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Sub CH,CH ; Set top byte to zero
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Mov AL,' ' ; Character to write
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Mov AH,0Ah ; Write blanks to screen
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Int 10h ; through BIOS
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Dummy: Ret
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; Insert and Delete
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; -----------------
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Insert: Xor [InsertOn],-1 ; Toggle the InsertOn flag
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Ret ; and return
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Delete: Call ShiftLeft ; Shift cursor line left
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Ret ; and return
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; Transfer Line on Screen to Keyboard Buffer
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; ------------------------------------------
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TransferLine: Sub CX,CX ; Count characters in line
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Mov DI,Offset KeyboardBuffer ; Place to store 'em
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Mov [BufferPointer],DI ; Save that address
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Cld ; String direction forward
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GetCharLoop: Mov AH,02h ; Set Cursor at DX
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Int 10h ; through BIOS
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Mov AH,08h ; Read Character & Attribute
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Int 10h ; through BIOS
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Stosb ; Save the character
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Inc CX ; Increment the counter
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Inc DL ; Increment the cursor column
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Cmp DL,[MaxCharCol] ; See if at end of line yet
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Jbe GetCharLoop ; If not, continue
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Dec DI ; Points to end of string
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Mov AL,' ' ; Character to search through
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Std ; Searching backwards
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Repz Scasb ; Search for first non-blank
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Cld ; Forward direction again
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Jz SetBufferCount ; If all blanks, skip down
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Inc CL ; Number of non-blanks
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Inc DI ; At last character
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SetBufferCount: Inc DI ; After last character
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Mov [BufferCounter],CL ; Save the character count
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Ret ; Return from routine
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; Shift Line One Space Right (For Insert)
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; ---------------------------------------
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ShiftRight: Push DX ; Save original cursor
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Mov DI,AX ; Character to insert
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ShiftRightLoop: Call ReadAndWrite ; Read character and write
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Inc DL ; Kick up cursor column
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Cmp DL,[MaxCharCol] ; Check if it's rightmost
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Jbe ShiftRightLoop ; If not, keep going
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Pop DX ; Get back original cursor
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Ret ; And return from routine
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; Shift Line One Space Left (For Delete)
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; --------------------------------------
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ShiftLeft: Mov DI,0020h ; Blank at end
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Mov BL,DL ; Save cursor column
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Mov DL,[MaxCharCol] ; Set cursor to end of line
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ShiftLeftLoop: Call ReadAndWrite ; Read character and write
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Dec DL ; Kick down cursor column
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Cmp DL,BL ; See if at original yet
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Jge ShiftLeftLoop ; If still higher, keep going
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Inc DL ; Put cursor back to original
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Ret ; And return from routine
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; Read and Write Character for Line Shifts
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; ----------------------------------------
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ReadAndWrite: Mov AH,2 ; Set Cursor from DX
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Int 10h ; through BIOS
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Mov AH,08h ; Read Character and Attribute
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Int 10h ; through BIOS
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Xchg AX,DI ; Switch with previous char
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Mov CX,1 ; One character to write
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Mov AH,0Ah ; Write character only
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Int 10h ; through BIOS
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Ret ; Return from Routine
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; Initialization on Entry
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; -----------------------
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Initialize: Sub AX,AX ; Make AX equal zero
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Mov DS,AX ; To point to vector segment
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Les BX,dword ptr DS:[21h * 4]; Get and save Int. 21h
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Mov Word Ptr CS:[OldInterrupt21],BX
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Mov Word Ptr CS:[OldInterrupt21 + 2],ES
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Les BX,dword ptr DS:[16h * 4]; Get and save Int. 16h
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Mov Word Ptr CS:[OldInterrupt16],BX
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Mov Word Ptr CS:[OldInterrupt16 + 2],ES
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Push CS ; Restore DS register
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Pop DS ; by setting to CS
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Mov DX,Offset NewInterrupt21
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Mov AX,2521h ; Set new Interrupt 21h
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Int 21h ; through DOS
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Mov DX,Offset NewInterrupt16
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Mov AX,2516h ; Set new Interrupt 16h
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Int 21h ; through DOS
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Mov DX,Offset Initialize ; Number of bytes to stay
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Int 27h ; Terminate & remain resident
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CSEG EndS
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End Entry
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