 %macro cmn 4			;common macro for input/output
	mov rax,%1
	mov rdi,%2
	mov rsi,%3
	mov rdx,%4
	syscall
%endmacro

section .data
	num db 00h
	msg db "Factorial is : "
	msglen equ $-msg
	msg1 db "**Program to find Factorial of a number** ",0Ah
		db "Enter the number : ",
	msg1len equ $-msg1
	nwline db 10

section .bss
	dispbuff resb 16
	numascii resb 3
	

section .text
global _start
_start:
	
	cmn 1,1,msg1,msg1len
	cmn 0,0,numascii,3			;accept number from user
	call convert			;convert number from ascii to hex
	mov [num],bl
	
	cmn 1,1,msg,msglen
	
	xor rdx,rdx
	xor rax,rax
	mov bl,[num]

	call proc_fact 

	mov rbx,rax
	
	call display

	mov rax,60
	mov rdi,0
	syscall

	proc_fact: 
	cmp bl, 1 
	jg do_calculation 
	mov ax, 1 
	ret 

	do_calculation: 
	dec bl 
	call proc_fact 
	inc bl 
	mul bl ;ax = al * bl 
	ret 




display:			; procedure to convert hex to ascii

mov ecx,16
mov edi,dispbuff
again:rol rbx,4
	mov al,bl
and al,0fh
cmp al,09h
jbe x1
add al,07h
x1:add al,30h
mov [edi],al
inc edi
loop again
cmn 1,1,dispbuff,16
cmn 1,1,nwline,1
	ret

	

convert:			;procedure to convert ascii to hex
mov rsi,numascii
mov cl,02h
xor rax,rax
xor rbx,rbx
contc:	rol bl,04h
mov al,[rsi]
cmp al,39h
jbe skipc
sub al,07h
skipc:
sub al,30h
add bl,al
inc rsi
dec cl 
jnz contc
	
ret

created 4 years ago

Assembly Online Compiler

Write, Run & Share Assembly code online using OneCompiler's Assembly online compiler for free. It's one of the robust, feature-rich online compilers for Assembly language. Getting started with the OneCompiler's Assembly compiler is simple and pretty fast. The editor shows sample boilerplate code when you choose language as Assembly and start coding.

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