%macro scall 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 zerofact db " 00000001 " zerofactlen equ $-zerofact section .bss dispnum resb 16 result resb 4 temp resb 3 section .text global _start _start: scall 1,1,msg1,msg1len scall 0,0,temp,3 ;accept number from user call convert ;convert number from ascii to hex mov [num],dl scall 1,1,msg,msglen xor rdx,rdx xor rax,rax mov al,[num] ;store number in accumulator cmp al,01h jbe endfact xor rbx,rbx mov bl,01h call factr ;call factorial procedure call display call exit endfact: scall 1,1,zerofact,zerofactlen call exit factr: ;recursive procedure cmp rax,01h je retcon1 push rax dec rax call factr retcon: pop rbx mul ebx jmp endpr retcon1: ;if rax=1 return pop rbx jmp retcon endpr: ret display: ; procedure to convert hex to ascii mov rsi,dispnum+15 xor rcx,rcx mov cl,16 cont: xor rdx,rdx xor rbx,rbx mov bl,10h div ebx cmp dl,09h jbe skip add dl,07h skip: add dl,30h mov [rsi],dl dec rsi loop cont scall 1,1,dispnum,16 ret convert: ;procedure to convert ascii to hex mov rsi,temp mov cl,02h xor rax,rax xor rdx,rdx contc: rol dl,04h mov al,[rsi] cmp al,39h jbe skipc sub al,07h skipc: sub al,30h add dl,al inc rsi dec cl jnz contc ret exit: ;exit system call mov rax,60 mov rdi,0 syscall ret
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.
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.
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.
There are various define directives to allocate space for variables for both initialized and uninitialized data.
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 |
| 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 can be defined using
CONSTANT_NAME EQU regular-exp or value
%assign constant_name value
%define constant_name value
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.
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