Question

In Assembly x86-64 write a code that receives user input of a number and calculates its factorial using a recursive subroutine.

Answer 1

A recursive subroutine in Assembly x86-64 to calculate the factorial of a number includes a base case, a recursive call, and multiplication steps to compute the factorial before the program exits.

Step-by-step explanation:

Assembly x86-64 Recursive Factorial

In Assembly x86-64, writing a code that calculates the factorial of a number using a recursive subroutine involves reading user input, a base case check, and the factorial calculation itself. Here is an example of how you might implement such a program:

segment .bss
resb 1
segment .text
global _start

_start:
; Read number from user
; ...

; Convert input to integer if necessary
; ...

; Call the factorial subroutine
call factorial

; Handle the result (e.g., print it)
; ...

; Exit the program
mov eax, 60 ; syscall for exit
xor edi, edi ; status 0
syscall

factorial:
; Argument: rdi - number
; Return: rax - factorial of the number
cmp rdi, 1
jle .base_case
dec rdi
push rdi
call factorial
pop rdi
mul rdi
ret

.base_case:
mov rax, 1
ret

This program's structure includes user input handling, the recursive factorial function, and the program exit sequence. The factorial function multiplies the number by the factorial of the number minus one until it reaches the base case where the number is less than or equal to 1, where it returns 1 (the factorial of 0 or 1).