HelloWorld.asm

 
.MODEL SMALL
.STACK 100H
.DATA
 
; The string to be printed
STRING DB 'abba', '$'
STRING1 DB 'String is palindrome', '$'
STRING2 DB 'String is not palindrome', '$'
 
.CODE
MAIN PROC FAR
 MOV AX, @DATA
 MOV DS, AX
 
 ; check if the string is;
 ;palindrome or not
 CALL Palindrome
 
 ;interrupt to exit
 MOV AH, 4CH
 INT 21H
 MAIN ENDP
 Palindrome PROC
 
 ; load the starting address
 ; of the string
 MOV SI,OFFSET STRING
 
 ; traverse to the end of;
 ;the string
 LOOP1 :
    MOV AX, [SI]
    CMP AL, '$'
    JE LABEL1
    INC SI
    JMP LOOP1
 
 ;load the starting address;
 ;of the string
 LABEL1 :
    MOV DI,OFFSET STRING
    DEC SI
 
    ; check if the string is palindrome;
    ;or not
    LOOP2 :
     CMP SI, DI
     JL OUTPUT1
     MOV AX,[SI]
     MOV BX, [DI]
     CMP AL, BL
     JNE OUTPUT2
 
    DEC SI
    INC DI
    JMP LOOP2
 
 OUTPUT1:
    ;load address of the string
    LEA DX,STRING1
 
    ; output the string;
    ;loaded in dx
    MOV AH, 09H
    INT 21H
    RET
 
 OUTPUT2:
    ;load address of the string
    LEA DX,STRING2
 
    ; output the string
    ; loaded in dx
    MOV AH,09H
    INT 21H
    RET
 
Palindrome ENDP
END MAIN

created 2 years ago

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About Assembly

Assembly language(asm) is a low-level programming language, where the language instructions will be more similar to machine code instructions.

Every assembler may have it's own assembly language designed for a specific computers or an operating system.

Assembly language requires less execution time and memory. It is more helful for direct hardware manipulation, real-time critical applications. It is used in device drivers, low-level embedded systems etc.

Syntax help

Assembly language usually consists of three sections,

Data section
To initialize variables and constants, buffer size these values doesn't change at runtime.
bss section
To declare variables
text section
_start specifies the starting of this section where the actually code is written.

Variables

There are various define directives to allocate space for variables for both initialized and uninitialized data.

1. To allocate storage space to Initialized data

Syntax

variable-name    define-directive    initial-value

Define Directive	Description	Allocated Space
DB	Define Byte	1 byte
DW	Define Word	2 bytes
DD	Define Doubleword	4 bytes
DQ	Define Quadword	8 bytes
DT	Define Ten Bytes	10 bytes

2. To allocate storage space to un-initialized data

Define Directive	Description
RESB	Reserve a Byte
RESW	Reserve a Word
RESD	Reserve a Doubleword
RESQ	Reserve a Quadword
REST	Reserve a Ten Bytes

Constants

Constants can be defined using

1. equ

To define numeric constants

CONSTANT_NAME EQU regular-exp or value

2. %assign

To define numeric constants.

%assign constant_name value

3. %define

To define numeric or string constants.

%define constant_name value

Loops

Loops are used to iterate a set of statements for a specific number of times.

mov ECX,n
L1:
;<loop body>
loop L1

where n specifies the no of times loops should iterate.

Procedures

Procedure is a sub-routine which contains set of statements. Usually procedures are written when multiple calls are required to same set of statements which increases re-usuability and modularity.

procedure_name:
   ;procedure body
   ret