ft_strdup.s

; **************************************************************************** ;
;                                                                              ;
;                                                         :::      ::::::::    ;
;    ft_strdup.s                                        :+:      :+:    :+:    ;
;                                                     +:+ +:+         +:+      ;
;    By: apuchill <apuchill@student.42sp.org.br>    +#+  +:+       +#+         ;
;                                                 +#+#+#+#+#+   +#+            ;
;                                                      #+#    #+#              ;
;                                                     ###   ########.fr        ;
;                                                                              ;
; **************************************************************************** ;

; ------------------------------------------------------------------------------
;    FUNCTION PROTOTYPE (man 3 strdup)
; char	*ft_strdup(const char *s1)
;
;    INPUT
; 1st argument:	rdi -> const char *s1
;
;    OUTPUT
; return:		rax -> char *dst
; ------------------------------------------------------------------------------

	global		ft_strdup

	extern		__errno_location
	extern		malloc
	extern		ft_strlen
	extern		ft_strcpy

	section		.text

ft_strdup:
	call		ft_strlen		; len = ft_strlen(s1)
	inc			rax				; len++ (increment for '\0')
	mov			rbx, rdi		; tmp = s1
	mov			rdi, rax		; size = len
	call		malloc			; ret_malloc = malloc(size)
	cmp			rax, 0
	je			.ret_error		; if (!ret_malloc) then ret_error()
	mov			rdi, rax		; dst = ret_malloc
	mov			rsi, rbx		; src = tmp (= s1)
	call		ft_strcpy
	ret

.ret_error:
	mov		rdi, rax			; tmp = ret
	neg		rdi					; tmp = -tmp (invert value for positive errno)
	call	__errno_location	; ret = &errno (get pointer to errno)
	mov		[rax], rdi			; *ret = tmp (put return value into errno)
	mov		rax, -1				; ret = -1
	ret							; return (ret)