initial commit, asm operating system with the MikeOS bootloader

source/features/strings.asm

@@ -0,0 +1,28 @@
+; 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:	
+	pusha
+
+.compare:
+	lodsb
+	scasb			; Compare di to si
+	jne .unequal		; If they are no 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
+	popa
+	ret
+
+.equal:
+	mov cl, 1
+	popa
+	ret