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https://github.com/vxunderground/MalwareSourceCode
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251 lines
8.1 KiB
NASM
251 lines
8.1 KiB
NASM
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TITLE scrn3.asm
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; AUTHOR Tim Spencer - Compuserve [73657,1400]
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; DATE March 17, 1987
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_TEXT SEGMENT BYTE PUBLIC 'CODE'
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_TEXT ENDS
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_DATA SEGMENT WORD PUBLIC 'DATA'
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SCRN STRUC ; screen data structure - defined in video.h
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off dw 0 ; offset (cursor position)
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seg dw 0 ; screen buffer address
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port dw 0 ; status port address
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attrib dw 0 ; attribute to use
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cgacrd dw 0 ; enable retrace checking if not zero
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SCRN ENDS
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_DATA ENDS
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DGROUP GROUP _DATA
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ASSUME CS:_TEXT, DS:DGROUP, SS:DGROUP, ES:NOTHING
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_TEXT SEGMENT BYTE PUBLIC 'CODE'
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;-----------------------------------------------------------------------;
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; scrn_restore - MSC callable function to restore a rectangular area ;
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; of the screen buffer. Checks for vertical retrace ;
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; only if the external structure member cga_card is ;
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; non-zero. &scrn is the address of that structure. ;
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; (see video.h). ;
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; ; ;
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; Note: This procedure uses stosb in retrace checking mode (instead of ;
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; movsb) because it stuffs the char/attrib into the screen buffer ;
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; slightly faster. ;
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; ;
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; Usage: scrn_restore(left, right, top, bottom, data_buff, &scrn) ;
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; ;
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;-----------------------------------------------------------------------;
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_DATA SEGMENT
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restore_args STRUC ; structure for easy argument reference
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dw 0 ; saved BP value
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dw 0 ; return address
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rleft dw 0 ; rectangular boundries...
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rright dw 0
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rtop dw 0
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rbottom dw 0
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mdata dw 0 ; address of data buffer to write to screen
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mstruct dw 0 ; pointer to SCRN structure(defined in video.h)
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restore_args ENDS
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cga db 0 ; variable to hold cga_card value
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_DATA ENDS
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PUBLIC _scrn_restore
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_scrn_restore PROC NEAR
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push bp ; set up frame pointer
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mov bp,sp
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push si
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push di
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mov bx,[bp].mstruct ; get pointer to SCRN structure
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les di,dword ptr[bx].off ; get scrn seg in es, off in di
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mov dx,[bx].port ; get status port address
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mov ax,[bx].cgacrd ; hold cga status in variable cga
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mov cga,al
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mov si,[bp].mdata ; make si point to data buffer
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mov bh,byte ptr[bp].rtop ; top will be incremented until it
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mov bl,byte ptr[bp].rbottom ; is greater than bottom, then exit.
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xor cx,cx ; set initial logical cursor position
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mov cl,bh ; by getting top into cx,
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mov al,80 ; multiplying by 80,
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mul cl
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mov cx,ax
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add cx,[bp].rleft ; adding left.
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shl cx,1 ; and multiplying by 2
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mov di,cx ; put result into di
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mov cx,[bp].rright ; get the length of one line into
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sub cx,[bp].rleft ; cx by subtracting left from right
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add cx,1 ; adding 1
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push cx ; save it
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mov ax,79 ; calculate offset from end of line to
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sub ax,[bp].rright ; the start of the next line
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add ax,[bp].rleft
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shl ax,1
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push ax ; and save it
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write_line:
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cmp cga,0 ; cga card in use?
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jnz rwait1 ; yes, go wait
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rep movsw ; no, warp speed.
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jmp short rcheck_pos ; go check position
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rwait1:
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in al, dx ; wait for end of retrace
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shr al, 1 ; test horizontal trace bit
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jc rwait1 ; loop if still tracing
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cli ; disable writus interuptus
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rwait2:
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in al, dx ; now wait until the very moment
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shr al, 1 ; when the next retrace begins
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jnc rwait2 ; still waiting...
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mov al,[si] ; load the char into al for stosb
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stosb ; write it and update pointer
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sti ; enable interrupts again
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inc si ; point si at attribute
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rwait3:
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in al, dx ; repeat these steps for the attribute
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shr al, 1
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jc rwait3
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cli
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rwait4:
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in al, dx
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shr al, 1
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jnc rwait4
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mov al,[si] ; load the attribute
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stosb
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sti
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inc si ; point si at next char
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loop rwait1
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rcheck_pos:
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pop ax ; restore offset to next line start
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pop cx ; restore count
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inc bh ; is top greater than bottom yet?
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cmp bh,bl
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ja rexit ; yes.
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push cx ; no, save count again
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push ax ; save line start offset again
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add di,ax ; move di to start of next line
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jmp short write_line ; write another line
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rexit:
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pop di
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pop si
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pop bp
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ret
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_scrn_restore ENDP
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;-----------------------------------------------------------------------;
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; scrn_save - MSC callable function to save a rectangular area of the ;
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; screen to a user defined buffer. ;
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; ;
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; Usage: scrn_save(left, right, top, bottom, data_buff, &scrn) ;
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;-----------------------------------------------------------------------;
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_DATA SEGMENT
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save_args STRUC ; structure for easy argument reference
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dw 0 ; saved bp value
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dw 0 ; return address
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sleft dw 0 ; rectangular boundries
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sright dw 0
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stop dw 0
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sbottom dw 0
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sbuff dw 0 ; user defined buffer to hold screen contents
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sstruct dw 0 ; pointer to SCRN structure (see video.h)
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save_args ENDS
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_DATA ENDS
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scga db 0 ; store cga true/false value here - must be
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; declared outside data segment because es and
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; ds are swapped in this function.
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PUBLIC _scrn_save
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_scrn_save PROC NEAR
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push bp ; set up frame pointer
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mov bp,sp
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push si
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push di
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push ds
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mov bx,[bp].mstruct ; get pointer to SCRN structure
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mov dx,[bx].port ; get status port address
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mov ax,[bx].cgacrd ; hold cga status in variable scga
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mov scga,al
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mov ax,ds
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mov es,ax ; get data segment into es
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mov di,[bp].sbuff ; and offset of user buffer in di
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mov ax,[bx].seg ; get the screen segment and
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mov ds,ax ; put in ds
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mov bh,byte ptr[bp].stop ; top will be incremented until it
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mov bl,byte ptr[bp].sbottom ; is greater than bottom, then exit.
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xor cx,cx ; set initial logical cursor position
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mov cl,bh ; by getting top into cx,
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mov al,80 ; multiplying by 80,
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mul cl
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mov cx,ax
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add cx,[bp].sleft ; adding left.
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shl cx,1 ; and multiplying by 2
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mov si,cx ; put result into si
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mov cx,[bp].sright ; get the length of one line into
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sub cx,[bp].sleft ; cx by subtracting left from right
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add cx,1 ; adding 1
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push cx ; save it
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mov ax,79 ; calculate offset from end of line to
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sub ax,[bp].sright ; the start of the next line
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add ax,[bp].sleft
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shl ax,1
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push ax ; and save it
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read_line:
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cmp cga,0 ; cga card in use?
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jnz swait1 ; yes, go wait
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rep movsw ; no, warp speed.
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jmp short scheck_pos ; go check position
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swait1:
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in al, dx ; wait for end of retrace
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shr al, 1 ; test horizontal trace bit
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jc swait1 ; loop if still tracing
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cli ; disable writus interuptus
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swait2:
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in al, dx ; now wait until the very moment
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shr al, 1 ; when the next retrace begins
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jnc swait2 ; still waiting...
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mov al,[si] ; load the char into al for stosb
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stosb ; write it and update pointer
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sti ; enable interrupts again
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inc si ; point si at attribute
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swait3:
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in al, dx ; repeat these steps for the attribute
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shr al, 1
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jc swait3
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cli
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swait4:
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in al, dx
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shr al, 1
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jnc swait4
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mov al,[si] ; load the attribute
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stosb
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sti
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inc si ; point si at next char
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loop swait1
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scheck_pos:
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pop ax ; restore offset to next line start
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pop cx ; restore count
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inc bh ; is top greater than bottom yet?
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cmp bh,bl
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ja sexit ; yes.
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push cx ; no, save count again
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push ax ; save line start offset again
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add si,ax ; move di to start of next line
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jmp short read_line ; write another line
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sexit:
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pop ds
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pop di
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pop si
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pop bp
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ret
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_scrn_save ENDP
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_TEXT ENDS
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END
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