Code: Select all
define SINCE_MIDNIGHT 0x406C //the address of since midnight ticks as found on a website
//Im assuming the bios keeps up with this and I dont need to call anything to gain access to this
start_make_random: //I've also tried 0x407F to get the last byte but that gives the same results
mov al,[SINCE_MIDNIGHT]
make_random:
sub al,4
cmp al,0x5
jge make_random //basically I'm finding SINCE_MIDNIGHT%4, I cmp it to 5 so I never get 0
ret Code: Select all
and al, 11b
inc al
Code: Select all
rand_int:
mov si,[seed_pos]
mov al,[si] //Stage one XORs three
mov di,[seed_pos+2]
mov ah,[di]
xor al,ah
mov di,[seed_pos+4]
mov ah,[di]
xor al,ah
and al,3
inc al
push ax
mov di,[seed_pos]
mov al,[di]
rol al,3
mov [di],al
mov ah,al
mov di,[seed_pos+2]
mov al,[di]
xor al,ah
and ah,al
rol al,7
mov [di],al
mov di,[seed_pos+4]
mov al,[di]
xor al,ah
rol al,5
mov [di],al
add si,9
call fix_seed_pos
mov [seed_pos],si
mov si,[seed_pos+2]
add si,4
call fix_seed_pos
mov [seed_pos+2],si
mov si,[seed_pos+4]
add si,7
call fix_seed_pos
mov [seed_pos+4],si
pop ax
ret
fix_seed_pos:
cmp si,0x7C00
jl fix_seed_pos_end
sub si,0x7C00
add si,RN_BUFFER
fix_seed_pos_end:
ret
. If I remember it correctly I found it in the appendix section of Robert Lowe's book Code: Select all
...
mov ch,0x0
mov cl,0x4
mov dh,0x0
mov dl,0x0
mov ax,0x0
mov es,ax
mov bx,0x500
mov ah,02h
mov al,0x1
int 13h
mov ah,0x0
mov al,0x13
int 10h
main:
call ddraw
jmp _end
...
times 510-($-$$) db 0
dw 0x55AA
org 0x500
ddraw:
mov ax,(VID_MEM_START)
mov es,ax
mov bx,0x0000
mov ax,15
mov [es:bx],ax
ret
Ddestroy:
mov ax,VID_MEM_START
mov es,ax
mov bx,0x0000
mov ax,0
mov [es:bx],ax
ret
_end:
times 512-($-$$) db 0
The ...s is where I cut the code that doesnt matter out but this is clearly in the code. It pans out to be AA55 in the hex.times 510-($-$$) db 0
dw 0x55AA