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x86 Assembly: Recursive Factorial

The document describes x86 assembly language code to calculate the factorial of a given integer number passed as a command line argument using recursion. The code uses explicit stack manipulation to recursively call a proc_fact subroutine, multiply the results, and output the final factorial value.

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Satyam Gawali
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16 views2 pages

x86 Assembly: Recursive Factorial

The document describes x86 assembly language code to calculate the factorial of a given integer number passed as a command line argument using recursion. The code uses explicit stack manipulation to recursively call a proc_fact subroutine, multiply the results, and output the final factorial value.

Uploaded by

Satyam Gawali
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
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Download as PDF, TXT or read online on Scribd
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;Write x86 ALP to find the factorial of a given integer number on a command line by

;using recursion. Explicit stack manipulation is expected in the code.

%macro IO 4
mov rax, %1
mov rdi, %2
mov rsi, %3
mov rdx, %4
syscall
%endmacro

section .data
msg db " Factorial is -> ",
l1 equ $ - msg

endline db "", 10
l2 equ $ - endline

base db "0001"
l3 equ $ - base

input db 06D ; Change the number to take different input


section .bss
dispbuff resb 16
result resb 4
num resb 1

section .text
global _start
_start:
IO 1, 1, msg, l1
mov al, [input]
cmp al, 01h
jbe endFact

mov bl, [input]


call proc_fact
mov rbx, rax
call print

IO 1, 1, endline, l2
call exit
ret

endFact:
IO 1, 1, base, l3
ret

print:
mov rdi, dispbuff
mov rcx, 16
repeat:
rol rbx, 4
mov dl,bl
and dl, 0fh
add dl, 30h
cmp dl, 39h
jbe skip1
add dl, 07h

skip1:
mov [rdi], dl
inc rdi
loop repeat
IO 1, 1, dispbuff, 16
ret

proc_fact:
cmp bl, 1
jne do_calc
mov ax, 1
ret

do_calc:
push rbx
dec bl
call proc_fact
pop rbx
mul bl
ret

exit:
mov rax, 60
mov rdi, 0
syscall
ret

; Output:
; Factorial is -> 00000000000002D0

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