How to deny or invert the memory address

Question

I'm doing some tasks and I need to solve the following problem: I need to load with a descending table, this table starts at the value 0000 and ends with ffff, for example:

Addres    value
0000      ffff
0001      fffe
0002      fffd
....      ....
....      ....
ffff      0000

My code:

mov ax,0000
mov bx,0000
not bx
mov ax,bx ; this is line 41
inc ax
dec bx
cmp ax,ffff
jne 41 
int 3

directly, this code does not work, does nothing. I don't have great knowledge in assembly and I can't detect the error.

Answer 1

Successive addresses store a single byte that can hold values from 0 to 255 . For the values from 0 to FFFFh that you want to store, you would need 131072 bytes (65536*2). In 16-bit mode (real address mode) a memory segment can have 65536 bytes making your task a bit complicated!

    cld
    xor     di, di    ; Address 0000h
    mov     ax, FFFFh ; Value
More:
    stosw
    dec     ax
    js      More

This will store 32768 descending word-values at offset addresses 0, 2, 4, 6, ... , 65534.
At this point you would have to change the ES segment register by adding 2048 to it.
Then continu with next code:

    ; DI=0 AX=7FFFh 
More_:
    stosw
    dec     ax
    jnz      More_

A byte solution is possible however:

    mov     bx, 0
    mov     al, 255
Next:
    mov     [bx], al
    inc     bx
    dec     al
    jnz     Next

    ; 0000  FF
    ; 0001  FE
    ; 0002  FD
    ;
    ; 00FE  01
    ; 00FF  00

A byte solution using 1 register:

    xor     bx, bx
 ext:
    mov     [bx], bl
    not     byte ptr [bx]
    inc     bx
    test    bl, bl
    jnz     Next

    ; 0000  FF
    ; 0001  FE
    ; 0002  FD
    ;
    ; 00FE  01
    ; 00FF  00