; How string comparison works
;                   DI => scasb compares value stored in DI which is 's' with 's' stored in AX register
;                         and then increments DI if DF is 0
;                    v
; memory address 1: |s|n|a|t|0|       
; memory address 2: |s|n|a|k|e|0|     
;                    ^
;                   SI => lodsb loads value stored at SI to AX and then increments SI if DF is 0
os_compare_strings:	
	cld

.compare:
	lodsb
	scasb			; Compare di to si
	jne .unequal		; If they are not equal, jump to .unequal
	cmp al, 0		; Check if string is finished
	je .equal		; If it has, return true
	jmp .compare		; Finally, repeat

.unequal:
	mov cl, 0		; Change to 0 if unquality is proven
	ret

.equal:
	mov cl, 1
	ret


; Convert a string to all upper case
os_upper_case:
    pusha
    mov di, si
.loop:
    lodsb
    inc di
    cmp al, 0
    je .finish
    cmp al, 7Ah
    jns .loop
    cmp al, 61h
    js .loop
    sub al, 20h
    dec di
    stosb
    jmp .loop
.finish:
    popa
    ret