Source code of Windows XP (NT5)
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;Copyright (c) 1998 - 1999 Microsoft Corporation
page 85,132
;*****************************************************************************
;
; yielddos.asm
; DOS TSR to yield when too many get time request float by
;
; Copyright Citrix Systems Inc. 1993
;
;
;*****************************************************************************
TEXT segment public 'CODE'
assume CS:TEXT,DS:TEXT,ES:TEXT,SS:Nothing
.286p
ORG 100h
main proc far
jmp init
main endp
;**************************************************************************
; Int21Hook
;
; Function: Int 21 Handler for yielddos
;
;**************************************************************************
Int21Hook proc far
; move current cmd to previous cmd
push ax
mov ah,cs:CurrCmd
mov cs:PrevCmd,ah
pop ax
; save current cmd
mov cs:CurrCmd,ah
; is request get time?
cmp ah,2ch
jne short NotMine
; move current time to previous time
push ax
mov ax,cs:CurrHourMin
mov cs:PrevHourMin,ax
mov ax,cs:CurrSec
mov cs:PrevSec,ax
pop ax
; get the current time
pushf
call dword ptr cs:[OldInt21]
pushf
; save the current time
push dx
and dl,0f0h ; look for changes within 16/100 sec
mov cs:CurrHourMin,cx
mov cs:CurrSec,dx
pop dx
; was the previous cmd Get Time?
cmp cs:PrevCmd,2ch
jne short NoYield
; are the times the same?
push ax
mov ax,cs:CurrHourMin
cmp ax,cs:PrevHourMin
pop ax
jne short NoYield
push ax
mov ax,cs:CurrSec
cmp ax,cs:PrevSec
pop ax
jne short NoYield
; yielding if time the same and command repeated
push ax
push cx
mov cx, cs:YieldCount
kbdJ:
mov ax,1680h
int 2fh
dec cx
jnz kbdJ
pop cx
pop ax
NoYield:
popf
retf 2
NotMine: ; send to previous Int 21 handler
jmp dword ptr cs:[OldInt21]
Int21Hook endp
;**************************************************************************
; Int33Hook
;
; Function: Int 33 Handler for yielddos
;
;**************************************************************************
Int33Hook proc far
; is request get button status and mouse position
cmp ax,0003h
jne short NotMine33
; get the mouse information
pushf
call dword ptr cs:[OldInt33]
pushf
; Count Int33 func 0003
inc cs:Int33Func3
push ax
push cx
mov cx, cs:YieldCount
mouseJ:
mov ax,1680h
int 2fh
dec cx
jnz mouseJ
pop cx
pop ax
popf
retf 2
NotMine33: ; send to previous Int 21 handler
jmp dword ptr cs:[OldInt33]
Int33Hook endp
OldInt21 dd 0 ; Old int 21 handler
OldInt33 dd 0 ; Old int 33 handler
Int33Func3 dw 0 ; Int33Func3 count
CurrCmd db 0 ; Current Int 21
PrevCmd db 0 ; Old Int 21
CurrHourMin dw 0 ; Current Hour/minutes
CurrSec dw 0 ; Current Sec/100th Sec
PrevHourMin dw 0 ; Previous Hour/minutes
PrevSec dw 0 ; Previous Sec/100th Sec
YieldCount dw 20 ; Yeild Loop Counter
ORG $ + 15
;*
;* End of resident code and data
;*
ResidentMark label byte
;*
;* Start of init code and data
;*
init:
; save regs
push ax
push bx
push cx
push dx
push si
; command line arg?
mov cl, byte ptr ds:[80h]
cmp cl, 0
je no_arg
; set up pointer and counter
mov si, 81h
xor bx, bx
jmp short getfirst
getnum:
dec cl
jz done
getfirst:
lodsb
sub al, "0"
jb not_int
cmp al, 9
ja not_int
cbw
xchg ax, bx
mov dx, 10
mul dx
add bx, ax
jmp getnum
not_int:
cmp bx, 0
je getnum
done:
cmp bx, 0
je no_arg
mov YieldCount, bx
no_arg:
pop si
pop dx
pop cx
pop bx
pop ax
; Hook Interrupt 21
call HookInt21
; Hook Interrupt 33
call HookInt33
StayRes:
; Free the environment
xor ax, ax
xchg ax, word ptr ds:[2ch] ; get env from PSP
or ax, ax
jz short skipenv
push es
mov es, ax
mov ah, 49h
int 21h
pop es
skipenv:
; Keep program running to catch Int 21 Func 3D requests
mov ax, 3100h
mov dx, offset ResidentMark
shr dx,4
int 21h
;*****************************************************************************
;* HookInt21
;*
;* Function: Hook Interrupt 21 for yielddos
;*
;* Notes:
;* Saves the Old Int 21 handler for restoring and calling
;*****************************************************************************
HookInt21 proc near
push es
push bx
push dx
mov ax,3521h ; get int 21 value
int 21h
mov word ptr [OldInt21],bx
mov word ptr [OldInt21]+2,es
mov ax,ds
mov es,ax
mov ax,2521h
mov dx, offset Int21Hook
int 21h
pop dx
pop bx
pop es
ret
HookInt21 endp
;*****************************************************************************
;* HookInt33
;*
;* Function: Hook Interrupt 33 for yielddos
;*
;* Notes:
;* Saves the Old Int 33 handler for restoring and calling
;*****************************************************************************
HookInt33 proc near
push es
push bx
push dx
mov ax,3533h ; get int 21 value
int 21h
mov word ptr [OldInt33],bx
mov word ptr [OldInt33]+2,es
mov ax,ds
mov es,ax
mov ax,2533h
mov dx, offset Int33Hook
int 21h
pop dx
pop bx
pop es
ret
HookInt33 endp
;*
;* Init DATA
;* messages and temporary storage discarded after init
;*
TEXT ends
end main