Adds strlen()

src/string.asm

@@ -1 +1,21 @@
 %include "src/constants.asm"
+
+section .text
+	global	strlen
+
+;----- strlen(*str[]) -----;
+; Gets the length of given string
+; Return value: Length of given string
+; Used registers:
+;	rax*	Byte to check in str[] >> (ret) length of given string
+;	rdi*	(arg) Pointer to str[]
+;	rcx*	Counter for scasb
+strlen:
+	xor	rax, rax
+	mov	rcx, -1
+	cld
+	repne	scasb
+	mov	rax, rcx
+	not	rax
+	dec	rax
+	ret