; The MIT License (MIT)
;
; Copyright (c) 2026 pacman64
;
; Permission is hereby granted, free of charge, to any person obtaining a copy
; of this software and associated documentation files (the "Software"), to deal
; in the Software without restriction, including without limitation the rights
; to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
; copies of the Software, and to permit persons to whom the Software is
; furnished to do so, subject to the following conditions:
;
; The above copyright notice and this permission notice shall be included in
; all copies or substantial portions of the Software.
;
; THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
; IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
; FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
; AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
; LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
; OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
; SOFTWARE.


; To compile this app for linux/amd64, use the commands
;
; nasm -f elf64 -o fail-linux-amd64.o fail-linux-amd64.asm
; ld -n -s fail-linux-amd64.o -o fail


; fail [code...]
;
; Do nothing but quit with the status code/number given as an argument; if no
; status code/number was given, quit using code 1 by default. If given 0 for
; the status code, it will paradoxically succeed, as 0 is the success code.


sys_exit equ 60

section .text

global _start

_start:

; rcx = argc
pop rcx

; just quit with the default code, if no arguments were given
cmp rcx, 1
mov rdx, 1
je quit

; skip argv[0]
pop rbx
; get argv[1]
pop rbx

; an empty string fails to parse: if so, quit with the default code
mov al, [rbx]
cmp al, 0
je bad_code

mov rdx, 0
mov rax, 0
parse_code:
    mov al, [rbx]
    cmp al, 0
    je quit

    cmp al, '0'
    jl bad_code
    cmp al, '9'
    jg bad_code

    imul rdx, 10
    sub al, '0'
    add rdx, rax

    inc rbx
    jmp parse_code

bad_code:
    mov rdx, 1

quit:
    ; exit(rdx)
        mov rax, sys_exit
        mov rdi, rdx
        syscall