hello2.asm

;; ---- HELP ----

;; Important functions:
;;   syscall    Call a system function. ID from `rax`, output to `rax`
;;              - See: https://github.com/torvalds/linux/blob/097f70b3c4d84ffccca15195bdfde3a37c0a7c0f/include/linux/syscalls.h
;;              - See: http://blog.rchapman.org/post/36801038863/linux-system-call-table-for-x86-64
;;
;;              - Examples:
;;                *   0     sys_read:   Read a value
;;                *   1     sys_write:  Output a value
;;                *  60     sys_exit:   Exit
;;
;; C functions:
;; -   0    long  sys_read  ( unsigned int fd,   char __user *buf,         size_t count );
;; -   1    long  sys_write ( unsigned int fd,   const char __user *buf,   size_t count );
;; -  60    long  sys_exit  ( int error_code                                            );

;; Compile and run with
;; ```sh
;;    nasm -f elf64 -o hello.o hello.asm
;;    ld -o hello hello.o
;;    ./hello
;; ```

;; Function variables:
;;  rax        CPU cache — temporary register. `syscal` uses this    Register: Accumulator
;;  rdi        CPU cache — 1st argument.                             Register: Destination Index
;;  rsi        CPU cache — 2nd argument.                             Register: Source Index
;;  rdx        CPU cache — 3rd argument.                             Register: D

;; Other variables:
;;  rbx   Register: Base index
;;  rcx   Register: Counter

;; Special variables:
;;  $     The current memory location

section .data                                      ;; Constants here
    ;; msg         db    "Hello, world!", 10       ;; Hello world variable as `msg`
    ;; len         equ   $ - msg                   ;; Length of `msg`
    
    NL          db    10
    
    namein      db    "Please enter your name", 10
    namein_     equ   $ - namein
    
    nameout0    db    "Hello, "
    nameout0_   equ   $ - nameout0
    
    nameout1    db    " !", 10
    nameout1_   equ   $ - nameout1
    
    
    name        times 512 db 0           ;; Buffer of 512 bytes
    
    exit        db    0
    
section .bss                             ;; Variables here
    name_       resd  0
    help        resd  0
    help2       resd  0
    help3       resd  0


section .text                            ;; Code here
    global      _start

_start:                                  ;; Initialize _start, then run

    ;; Get input and save as `name`
    mov     rax,  0
    mov     rdi,  0
    mov     rsi,  name
    mov     rdx,  512
    syscall
    
    ;; Get length of input
    mov     [name_],  rax
    
    
    ;; Output name_ as number
    mov     help,  1
    mov     help2, 0
    mov     help3, 0
    
    output_name_:
    
      ;; Make the help variable 
      make_help:
        ;; help *= 10
        mov help2, help
        mov help,  0
        times 10 add help, help2
    
        ;; help <= name_
        cmp help, name_
        jle make_help
        
      mov rdx, help
      div 10
      mov help, rdx
      
      mov help2, name_
      
      
      repeat:
        mov rdx, help2
        div help
        mov help3, rdx
      
        ; help2 -= help*help3
        ; help /= 10
        
        
        ; if help == 0: help = -1
        cmp help, 0
        jne skip
          mov help, -1
        skip:
      
        mov help3, help3 + 0x30 ; Convert number to ASCII
        
        ; If help2 >= 0: repeat
        cmp help2, 0
        jge repeat
      
        
        
        
        
    
    
    ;; Output nameout0
    mov     rax,  1
    mov     rdi,  1
    mov     rsi,  nameout0
    mov     rdx,  nameout0_
    syscall
    
    ;; Output name
    mov     rax,  1
    mov     rdi,  1
    mov     rsi,  name
    mov     rdx,  name_
    syscall
    
    ;; Output nameout1
    mov     rax,  1
    mov     rdi,  1
    mov     rsi,  nameout1
    mov     rdx,  nameout1_
    syscall

    ;; Output msg
    ;;mov     rax,  1
    ;;mov     rdi,  1
    ;;mov     rsi,  msg
    ;;mov     rdx,  len
    ;;syscall
    
    
    
eof:  ;; End Of File: Exit with 0

    ;; Exit with statuscode 0
    mov     rax,  60
    mov     rdi,  0
    syscall