Question

I am writing a program to print out all the numbers from 0 to 100, and I need to find the number of digits a variable(in this case the variable counter) holds.

Here is my code:

SECTION .data
len EQU 32

SECTION .bss
counter resd len 
digit1 resd len
digit2 resd len
digit3 resd len

SECTION .text
GLOBAL _start
_start:
nop

Print:
mov eax, 4
mov ebx, 1
mov ecx, counter
mov edx, len
int 80h 

Set:
mov BYTE [counter], 1

Divide:
; HERE IS WHERE I NEED TO FIND THE LENGTH OF THE VARIABLE COUNTER
; initial division
mov ax, [counter]   ; number we want to print
mov ch, 10    ; we divide by ten to siphon digits
div ch        ; divide our number by 10

; al now has 11, ah has 1
mov dh, ah             ; save the remainder in dh
xor ah,ah
mov ch, 10             ; refill ch with the divisor
div ch                 ; al now has 1, ah now has 1

Move:                     ; now to move our digits to a printable state
mov [digit1], dh      ; first digit is in edx
mov [digit2], ah
mov [digit3], al

Adjust:
add BYTE [digit1], '0'
add BYTE [digit2], '0'
add BYTE [digit3], '0'

Print:
mov eax, 4
mov ebx, 1
mov ecx, digit1
mov edx, len
int 80h

mov eax, 4
mov ebx, 1
mov ecx, digit2
mov edx, len
int 80h

mov eax, 4
mov ebx, 1
mov ecx, digit3
mov edx, len
int 80h

Exit:
mov eax, 1
mov ebx, 0
int 80h

I need to find the length so that I know how many times to divide and also how many digits to print the variable counter.

How can I find how long it is?

Thanks in advance

Answer 1

For numbers in the range 0..100, I’d just compare at the boundaries, with pseudo-assembler like:

    mov ax, [counter]

    mov cx, 3             ; default length
    cmp ax, 100           ; >= 100, use 3
    bge done

    dec cx                ; set length to 2
    cmp val, 10           ; >= 10, use 2
    bge done

    dec cx                ; set length to 1

done:
                          ; cx now holds the digit count.

That will actually handle up to 999 but you could also add more condition checks before the 100 one if you wanted to expand the range.