Assignment 9

%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
OUTPUT:
main.asm:124: warning: label alone on a line without a colon might be in
error [-w+label-orphan]
Program to find Factorial of a number
Enter the number : Factorial is : 0000000000000078
[Execution complete with exit code 0]