Convert Integer Into ASCII Assembly language Example

Posted by Suraj Singh on December 23, 2018 · 11 mins read
Hi readers,



Welcome Again readers, . I hope You all are Enjoying Series of Assembly Tutorials Well, Actually Assembly Is Very Important Part To Keep Strong Grep Over Exploit writing. that's why I am trying To Polish my Assembly Programming Writing Skill. So, Today Again I am going To share Another piece of Code Of Assembly language Where I tried To Demonstrate How To Convert Digits Into ASCII codes To Print Over the Terminal. I know, many of you are now confused. why?

Introduction


Actually, In Assembly, Printing Things Over the Terminal is Not that straight forward. When we print number in other high level programming language then, that programming language automatically handles all internal process. so, that user don't need to mess with low level process. but in assembly you have to done all on your own. So, basically In  assembly you actually can print only according to ASCII Table. Basically, All Your Hard Coded String, Character Automatically Gets Converted Into ASCII Table During Compilation By Compilers. But Note. Its Only Hard Coded Codes, Hence If Any Digit Gets Generated During Any Process Then You Have To Write Your Own Sub Routine To Convert it Into ASCII Code. I hope Now You All Got it. So, Let's Try It now.

How?

Read Comments Carefully!


By The Way, If you Are new And Don't Know How To Start, Compile Or Run?
Then, Don't Follow up Our Previous Blog post. Here, it's The List.

1. Hello World In Assembly
2. Find String Length In Assembly Language
3. Subroutine Demo In Assembly language
4. Some Subroutine Functionality Example
5. User Input Example In Assembly Language
6. Variable Decleration/Include function In Assembly


Convert Integer To ASCII Table In Assembly Language

Digit Printing Script (DigitPrinting.asm)

;    Digit printing concept
; author : Suraj Singh Bisht
; Email : surajsinghbisht054@gmail.com
;
; includable functions
%include 'includable_functions_without_start.asm'
;
; I Think This Script needs Little Finishing.
;
; So, i will left this work to reader :))
;
;
; ====================================================
; [ Includable File]
; Functions:
; _strlen
; _exit
; _print
; _printline
;
; ====================================================
;
;
; Simple Concept to print multi digit numbers
;
; For Example :
; Dividend = 1000 (Dividend)
; Divisor = 10
;
; ( Quotient, Remainder ) = ( Dividend / Divisor )
;
;
; While (if Quotient is Not Equal To 0){
; print (Remainder);
;
; ( Quotient, Remainder ) = ( Quotient / Divisor )
;
; }
;
;
;
; Come On! Use Mind And Calculate Above Provided Algo.
;
;

__printreverse:
; input
; eax = address of string
;
; output
; nothing
push ebx
push ecx
push edx

; store value into stack
push eax
call _strlen ; Find String length
mov ecx, eax ; ECX = Length Of String
pop ebx ; EBX = Address of string

_printreverseiterate:
mov al, [ebx+ecx] ; Load Address Into EAX
call _printsingle ; print single number over terminal
cmp ecx, 0 ; Compare if ECX is zero
je _printreversereturn ; Return
dec ecx
jmp _printreverseiterate ; Repeat


_printreversereturn:
pop edx
pop ecx
pop ebx
ret


; routine to print single digit
_printsingle:
; Input:
; EAX = Value
; Output:
; nothing
push ebx ; store register into stack

mov ebx, 0 ; EBX = 0
push ebx ; push ebx
push eax ; push eax
mov eax, esp ; EAX = ESP
call _print ; call print

pop eax ; pop Eax
pop ebx ; pop EBX Null Value
pop ebx ; pop eax

ret ; return


; Digit To ASCII Digit Convertion Subroutine
_printdigit:
; Input:
; EAX = Digit Number
; Output
; EAX
;

; Save Values
push eax ; Save Digit [Previous Arguments]
push ebx ; Push Ebx To Stack [Previous Arguments]
push ecx
push edx
mov ebx, 10 ; Set EBX = 10
mov ecx, 0 ;

; division loop
_divisionloop:
xor edx, edx ; EDX = 0
div ebx ; Perform Division Between EAX, EBX [EDX, EAX = EAX / EBX ]
; EAX = Quotient And EDX = Remainder

push eax ; Push EAX Into Stack [Division Answer]
mov eax, edx ; EAX = EDX [EAX = Remainder]

add eax, 48 ; ASCII code Difference Is 48
mov [digitprintersave+ecx], eax ;
;call _printsingle ; Call printsingle routine
inc ecx;
pop eax ; Get EAX
cmp eax, 0 ; Compare
je _comparisionsection ; To Avoid Print
jmp _divisionloop ; Repeat


_comparisionsection:
mov eax, digitprintersave ;
call __printreverse
; Pop Values
pop edx
pop ecx
pop ebx ; Pop Digit [Previous Arguments]
pop eax ; Pop Digit[Previous Arguments]

ret ; Return





; section bss
SECTION .bss

; section data
SECTION .data

; section text
SECTION .text
global _start


_iterateNumber:
; print digit routine
call _printdigit ; call _printdigit

; increase number
inc eax ; increase EAX = EAX + 1

; Compare
cmp eax, 100 ; Compare EAX==0, if Yes, Set Zero Flag = 1 Else Zero Flag = 0


; Check, Zero Flag
jne _iterateNumber ; Jump if not Equal _iterateNumber

; Exit Routine
jmp _exit


_start:
mov eax, 0 ; EAX = 0
jmp _iterateNumber ;

Includable Function (includable_functions_without_start.asm)

; Assembly Includable File
; author : suraj singh bisht
; Email : surajsinghbisht054@gmail.com
;
; ====================================================
; [ Includable File]
; Functions:
; _strlen
; _exit
; _print
; _printline
;
; ====================================================





; Routine To Find String length
_strlen:
; Input
; EAX = address of string
; Output
; EAX = Length of String

; Initialize Registers
push ebx ; push ebx value into stack
mov ebx, 0 ; Set EBX = 0


; iteration Routine
_iterate:
cmp byte [eax], 0 ; Compare Last bit, if true, Set Zero flag = 1 Else Zero flag = 0
jz _return ; If Zero Flag = 1, Then Call function else pass
inc eax ; Move Memory Address Pointer
inc ebx ; Keep Record of Iteration
jmp _iterate ; Repeat

; Return String Calculated Length
_return:
mov eax, ebx ; Set Return Value EAX = EBX
pop ebx ; POP EBX Value
ret ; Return

; Exit Routine
_exit:
mov eax, 1 ; Invoke SYS_EXIT
mov ebx, 0 ; set Return Value Zero
int 80h ; interpt kernel


; Print Line
_print:
; Input
; EAX = addressof(string)
; Output
; Nothing

push ebx ; Store Registers Into Stack
push ecx
push edx
push eax

call _strlen ; Find String Len
mov edx, eax ; Set EDX= EAX {String Length}
mov eax, 4 ; invoke SYS_WRITE
mov ebx, 1 ; STDOUT
pop ecx ; POP String Address
int 80h ; interpt Kernel
pop edx ; POP all registers previous values
pop ecx ;
pop ebx ;
ret ; return

; PrintLine
_printline:
; Input
; EAX = addressof(string)
; Output
; nothing

call _print ; Print String

;
mov eax, 0 ; SET EAX = 0
push eax ; PUSH EAX Into Stack To make Sure; String End Character is 0

mov eax, 0AH ; New Line ASCII Code
push eax ; Push into The Stack

;
; Now Our Stack Look Like This
; -> -> -> -> ->
; ---------------------------------------------------
; | EAX[0AH] | EAX [0] | previous data |
; ---------------------------------------------------
; ESP EBP
;

mov eax, esp ; Set EAX = ESP
call _print ; call _print routine
pop eax ; Remove not useful pushed values from stack
pop eax ;
ret ; Return



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