Question

Write an assembly program that will create a word namely “number” and assign it a value of 0x000F. [Remember this value is stored in binary form in the computer] Your program should store the binary representation of the ‘number’ in a ‘strOut’ variable and do the sys_write call to print

out the binary representation in the standard output in 16 bit form.

The output will look like this

0000000000001111

Answer 1

section .text
   global _start          ;must be declared for linker (gcc)
        
_start:                   ;tell linker entry point
   mov  edx,1             ;message length
   mov  ecx,strIut        ;message to write
   mov  ebx,1             ;file descriptor (stdout)
   mov  eax,4             ;system call number (sys_write)
   int  0x80              ;call kernel

   mov  eax,1             ;system call number (sys_exit)
   int  0x80              ;call kernel

section .data
strOut DB 'number'

   cx = 16   ; 16 bits to output
bin_loop:
    rcl al,1 ; move most significant bit into CF
    setc bl  ; bl = 0 or 1 by CF (80386 instruction)
    add bl,'0' ; turn that 0/1 into '0'/'1' ASCII char
    call display_bl ; must preserve al and cx
    loop bin_loop