10.3: Implement the Program

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Based on the algorithm, a program can be developed and implemented. The algorithm is expanded and the code added based on the steps outlined in the algorithm. This allows the programmer to focus on the specific issues for the current section being coded including the data types and data sizes. This example addresses only unsigned data so the unsigned divide (DIV, not IDIV) is used. Since the integer is a double-word, it must be converted into a quadword for the division. However, the result and the remainder after division will also be a double-words. Since the stack is quadwords, the entire quadword register will be pushed. The upper-order portion of the register will not be accessed, so its contents are not relevant.

One possible implementation of the algorithm is as follows:

;  Simple example program to convert an
;  integer into an ASCII string.

; *********************************************************
;  Data declarations

section .data 

; -----
;  Define constants

NULL                equ    0
EXIT_SUCCESS        equ    0                   ; successful operation
SYS_exit            equ    60                  ; code for terminate

; -----
;  Define Data.

intNum         dd     1498
section        .bss
strNum            resb    10

; *********************************************************

section         .text 
global     _start 
_start:

; Convert an integer to an ASCII string.

; -----
;  Part A - Successive division

    mov     eax, dword [intNum]         ; get integer
    mov     rcx, 0                      ; digitCount = 0
    mov     ebx, 10                     ; set for dividing by 10

divideLoop:
    mov    edx, 0
    div    ebx                          ; divide number by 10
    
    push   rdx                          ; push remainder
    inc    rcx                          ; increment digitCount
    
    cmp    eax, 0                       ; if (result > 0)
    jne    divideLoop                   ;   goto divideLoop
    
; -----
;   Part B - Convert remainders and store

    mov    rbx, strNum                   ; get addr of string
    mov    rdi, 0                        ; idx = 0
    
popLoop:
    pop    rax                           ; pop intDigit
    
    add    a1, "0"                       ; char = int + "0"
    
    mov    byte [rbx+rdi], a1            ; string[idx] = char
    inc    rdi                           ; increment idx
    loop   popLoop                       ; if (digit Count > 0)
                                         ;   goto popLoop
    mov    byte [rbx + rdi], NULL        ; string[idx] = NULL
    
    ; -----
    ; Done, terminate program.
    
    last:
         mov    rax, SYS_exit            ; call code for exit
         mov    rdi, EXIT_SUCCESS        ; exit with success
         syscall

There are many different valid implementations for this algorithm. The program should be assembled to address any typos or syntax errors.