global readf 

section .text
readf:
	push	rbp
	mov	rbp,rsp
	push	rbx
	push	rcx
	push	rdx
	push	rsi
	push	rdi

	mov	rbx,[rbp+32] ; filename
	mov	rax,5 ; sys_open
	mov	rcx,0 ; O_RDONLY
	int	0x80

	cmp	rax, -4096
	ja	ferror
	mov	rsi,rax ; fd
	
	mov	rax,19 ; sys_lseek
	mov	rbx,rsi ; fd
	mov	cx,[rbp+40] ; offset
	mov	rdx,1 ; SEEK_CUR
	int	0x80

	mov	rax,3 ; sys_read
	mov	rbx,rsi ; fd
	mov	rcx,[rbp+16] ; buffer
	mov	rdx, 4 ; buffer_size
	int	0x80

	mov	rax,6 ; sys_close
	mov	rbx,rsi  ; fd

	xor	bl,bl
	xor	ax,ax
	xor	rcx,rcx
	xor	rdx,rdx

	mov	cx,4
	mov	rdi,[rbp+16]
hextoi:	
	mov	al, byte [rdi+rcx-1]
	cmp	al, 0xa
	je	loend	
	cmp	al, 'A'
	jl	digit
	cmp	al, 'F'
	jg	ferror	
	sub	al, 'A'-10
	jmp	addd
digit:	
	cmp 	al, '0'
	jl	ferror
	cmp	al, '9'
	jg	ferror
	sub	al, '0'	
addd:	
	mov	si, cx
	mov	cl, bl
	shl	ax, cl
	mov	cx, si

	add	bl, 4
	add	dx, ax
loend:		
	loop	hextoi
	mov	rax,[rbp+24]
	mov	[rax],dx
	mov	rax,0
	jmp	fend
ferror:	
	mov	rax,1	
fend:	
	pop	rdi
	pop	rsi
	pop	rdx
	pop	rcx
	pop	rbx
	pop	rbp
	ret	32