section	.text
	global	strlen
	global	strcpy
	global	strcat

;----- strlen(char* str) -----;
; return value: amount of characters before EOS was found
strlen:
	push	rbp
	mov	rbp, rsp

	xor	rax, rax
	.findEOS:
		cmp	byte [rdi+rax], 0x0
		je	.quit
		inc	rax
		jmp	.findEOS

	.quit:
	leave
	ret
;----- strcpy(char* dest, char* src) -----;
; return value: pointer to dest or NULL if nothing was copied
strcpy:
	push	rbp
	mov	rbp, rsp

	xor	rax, rax
	xor	rcx, rcx
	.loop:
		cmp	byte [rsi], 0x0
		je	.0f
		mov	r10b, byte [rsi]
		mov	byte [rdi], r10b
		inc	rsi
		inc	rdi
		inc	rcx
		jmp	.loop
	mov	byte [rdi], 0x0

	.0f:
	cmp	rcx, 0
	jne	.quit
	xor	rax, rax

	.quit:
	leave
	ret
;----- strcat(char* dest, char* src) -----;
; return value: pointer to dest
strcat:
	push	rbp
	mov	rbp, rsp

	push	rdi
	sub	rsp, 8
	call	strlen
	add	rdi, rax
	call	strcpy
	add	rsp, 8
	pop	rax

	leave
	ret