Assignment 3

%macro print 4 ; simple macro ,
mov rax,%1 ; -> system call number
mov rdi,%2 ; -> file descriptor
mov rsi,%3 ; -> message
mov rdx,%4 ; -> length
syscall
%endmacro
section .data
m1 db "enter string",10 ;10 ->line feed
l1 equ $-m1 m2 db "Entered String is ",10 l2 equ$-m2
m3 db "Length is ",10
l3 equ $-m3 m4 db "Write an X86/64 ALP to accept a string and to display its length" ,10 l4 equ$-m4

section .bss
string resb 50 ;string array of size 50
strl equ $-string
count resb 1
_output resb 16
section .text
global _start

_start:
print 1,1,m4,l4 ; display
print 1,1,m1,l1 ; display
input:
print 0,0,string,strl
mov [count],rax ;count now points to rax
output:
print 1,1,m2,l2 ; display
print 1,1,string,strl
print 1,1,m3,l3 ; display
mov rax,[count] ; value of count passed into rax
call hex_to_dec
print 1,1,_output,16

exit:
mov rax, 60 ; system call for exit
mov rdi, 0 ; exit code 0
syscall

hex_to_dec:
mov rsi,_output+15 ; max size of display , for convinience set to 16 and rsipoints to output[16]
mov rcx,2 ; loop count , or number of digits displayed , 2 digits (unlikely we will enter string > 99)(prints preceding zeros otherwise)
letter2:
xor rdx,rdx ; setting rdx to null without setting a null byte (a tip i saw on reddit) needed to clean dl for use
mov rbx,10 ; conversion base
div rbx ; dividing by conversion base
cmp dl,09h ; comparing 09h with dl , since the division remainder ends up in dx and since its one digits its in dl
jbe add30 ; if value under in 0-9 , we directly add 30h to get ascii 0-9
add30:
add dl,30h ; adding 30h
mov [rsi],dl ; moving the ascii we generated to rsi
dec rsi ; rsi now points to the next place in display or output[n-1]
dec rcx ; loop
jnz letter2
ret