mirror of
https://github.com/vxunderground/MalwareSourceCode
synced 2024-06-28 18:02:48 +00:00
99 lines
3.0 KiB
NASM
99 lines
3.0 KiB
NASM
; Resident program to provide flicker-free write_tty scroll for Color
|
||
; Graphics Adapter clones with dual-ported memory. M. Abrash 5/3/86.
|
||
; Make runnable with MASM-LINK-EXE2BIN.
|
||
cseg segment
|
||
assume cs:cseg
|
||
org 100h ;necessary for COM file
|
||
start proc near
|
||
jmp makeres
|
||
old_int10 dd ?
|
||
; front end routine for BIOS video handler to scroll without flicker
|
||
scroll_front_end:
|
||
cmp ax,0e0ah ;only intercept write_tty function
|
||
jnz pass_to_bios ; called with linefeed
|
||
push ax
|
||
push bx
|
||
mov ah,0fh
|
||
int 10h ;get current page & mode
|
||
cmp al,2
|
||
jz check_row ;BIOS only blanks in modes 2 & 3, so
|
||
cmp al,3 ; only intercept linefeed scroll in
|
||
jnz pass_to_bios2 ; modes 2 & 3
|
||
check_row: ;see if cursor is on bottom row, in
|
||
push cx ; which case linefeed causes scroll
|
||
push dx
|
||
mov ah,3
|
||
int 10h ;get cursor location in current page
|
||
cmp dh,24
|
||
jnz pass_to_bios3 ;cursor not on bottom row, no scroll
|
||
push ds ;meets all the criteria, so perform
|
||
push es ; scroll in current page with special
|
||
push si ; routine that doesn't disable video
|
||
push di
|
||
mov ah,0fh
|
||
int 10h ;get # columns & page
|
||
mov al,ah
|
||
sub ah,ah ;convert to word
|
||
push ax ;set aside # columns
|
||
mov si,ax
|
||
shl si,1 ;move from second row (each character=2 bytes)
|
||
mov ah,24
|
||
mul ah ;# words to move (24 rows)
|
||
mov cx,ax
|
||
sub ax,ax ;now adjust offsets for current page
|
||
mov ds,ax ;buffer length is stored in BIOS segment
|
||
mov al,bh ;get current page
|
||
mul word ptr ds:[44ch] ;offset of start of current page
|
||
add si,ax ;move data from second row of current page
|
||
mov di,ax ; to top of current page
|
||
mov ax,0b800h
|
||
mov ds,ax
|
||
mov es,ax ;will move data in display segment
|
||
cld
|
||
rep movsw ;scroll screen up
|
||
mov ah,8 ;BH already has current page
|
||
int 10h ;get attribute of character at cursor
|
||
mov al,' ' ;fill with blanks & attribute just obtained
|
||
pop cx ;# of words per row
|
||
rep stosw ;blank bottom row-DI points to bottom row
|
||
pop di ;done
|
||
pop si
|
||
pop es
|
||
pop ds
|
||
pop dx
|
||
pop cx
|
||
pop bx
|
||
pop ax
|
||
iret
|
||
pass_to_bios3:
|
||
pop dx
|
||
pop cx
|
||
pass_to_bios2:
|
||
pop bx
|
||
pop ax
|
||
pass_to_bios: ;pass interrupt to normal BIOS handler
|
||
jmp cs:[old_int10]
|
||
endres:
|
||
; make scroll front end handler resident & revector interrupt 10 to it
|
||
makeres:
|
||
push cs
|
||
pop ds
|
||
assume ds:cseg
|
||
mov ax,3510h ;DOS get vector function, vector 10h
|
||
int 21h ;get vector 10h
|
||
mov word ptr [old_int10],bx ;set aside old vector to
|
||
mov word ptr [old_int10+2],es ; allow pass to BIOS
|
||
mov ax,2510h ;DOS set vector function, vector 10h
|
||
mov dx,offset scroll_front_end ;revector interrupt
|
||
int 21h ; 10h to front end routine
|
||
mov dx,offset endres ;# of paragraphs to make
|
||
mov cl,4 ; resident-can't do with an
|
||
shr dx,cl ; expression because assembler can't
|
||
inc dx ; calculate w/relocatable label
|
||
mov ax,3100h ;DOS make resident fn, exit code=0
|
||
int 21h ;terminate & stay resident
|
||
start endp
|
||
cseg ends
|
||
end start
|
||
|
||
|