Adds strcmp() (note: much different than strcmp in C)

src/string.asm

@@ -5,6 +5,7 @@ section .text
 	global	strcpy
 	global	strcat
 	global	strclr
+	global	strcmp
 
 ;----- strlen(*str[]) -----;
 ; Gets the length of given string
@@ -102,3 +103,43 @@ strclr:
 	cld
 	rep	stosb
 	ret
+
+;----- strcmp(*str1[], *str2[]) -----;
+; Compares str2 against str1
+; Return values:
+;	0			Two strings are the same, OR str1 or str2 is empty
+;	Length of str1		str2 is longer than str1, but no difference was found in between str1 and str2 -up to the point str1 ended-
+;	Anything else		Position (index+1) where str1 and str2 differ
+; Used registers:
+;	rax*	(ret)
+;	rdi	Pointer to str1
+;	rsi	Pointer to str2
+;	rcx*	Counter for scasb
+;	rdx*	Length of str1
+;	r8* 	Backup for rdi
+strcmp:
+	mov	rax, -1
+	cmp	byte [rdi], EOS
+	je	.equal
+	cmp	byte [rsi], EOS
+	je	.equal
+
+	mov	r8, rdi
+	call	strlen
+	mov	rcx, rax
+	mov	rdx, rax
+	mov	rdi, r8
+	cld
+	repe	cmpsb
+	je	.equal
+	mov	rax, rdx
+	sub	rax, rcx
+	jmp	.quit
+
+	.equal:
+	cmp	byte [rsi], EOS
+	jne	.quit
+	mov	rax, -1
+
+	.quit:
+	ret