[Assembly] strlen function

; SHOULD put the length of the string pointed to by bp in cx
strlen:

	push es				; Save the values of modified variables on the stack
	push bx

	mov bx,bp
	mov es,bp			; Set es to the pointer

strlen_loop:				; The loop sub

	cmp byte[es:0],0x00		; If the next character is 0x00, then there are no more characters!
		je strlen_end		; Jump to the end

	inc cx				; Increment the length
	inc bx				; Increment the string pointer
	mov es,bx

	jmp strlen_loop			; Repeat!

strlen_end:				; the end sub

	pop bx
	pop es				; Restore modified variables

	ret				; return

; SHOULD put the length of the string pointed to by bp in cx
strlen:
	push ax

	mov di,bp			; scasb scans the byte at byte[di], so we need to put the poitner there

	xor cx,cx			; scasb stores the length in cx
	not cx				; it decrements so we need to set it up first
	cld				; clear the direction flag so we go forwards in the string
	xor al,al			; scasb compares with al, so make al 0
	repne scasb			; keep repeating scasb until the byte and al are equal (you find zero)

	not cx				; It was counting down from 65535. So if it was 32 characters, it would be 65503, not = 32
	dec cx				; We don't want to count the trailing 0x00

	pop ax

	ret