Adds strfind

src/string.asm

@@ -6,6 +6,7 @@ section .text
 	global	strcat
 	global	strclr
 	global	strcmp
+	global	strfind
 
 ;----- strlen(*str[]) -----;
 ; Gets the length of given string
@@ -149,3 +150,58 @@ strcmp:
 
 	.quit:
 	ret
+
+;----- strfind(*str[], *what[], start_at) -----;
+; Finds string inside another string.
+; Return values: 0 if what[] wasn't found within str[]. Position (index+1) where first character was found in str[] otherwise
+; Used registers:
+;	rax*	(ret)
+;	rdi	(arg) Pointer to str[]
+;	rsi	(arg) Pointer to what[]
+;	rdx	(arg) Where to start looking in str[] (index)
+;	rcx*	Keeps track of current position in str[]
+;	r8*	Stores index where first character match of what[] was found
+;	r9*	Used to move byte for cmp instruction
+;	r10*	Keeps track if there is currently a match between str[] and what[]
+;	r11*	Backup for original pointer to what[]
+strfind:
+	xor	rax, rax
+	mov	rcx, 1
+	add	rcx, rdx
+	add	rdi, rdx
+	xor	r10b, r10b
+	mov	r11, rsi
+	.findStr:
+		cmp	byte [rsi], EOS
+		je	.testFullMatch
+		cmp	byte [rdi], EOS
+		je	.quit
+
+		mov	r9b, byte [rsi]
+		cmp	byte [rdi], r9b
+		jne	.noMatch
+
+		;.hasMatch:
+		test	r10b, r10b
+		jnz	.notFirstChar
+		mov	r10b, 1
+		mov	r8, rcx
+		.notFirstChar:
+		inc	rsi
+		jmp	.continueLoop
+
+		.noMatch:
+		; not gonna figure out here if there was an existing match already. just XOR r10b,r10b and load original pointer to what[] to rsi
+		xor	r10b, r10b
+		mov	rsi, r11
+
+		.continueLoop:
+		inc	rdi
+		inc	rcx
+		jmp	.findStr
+	.testFullMatch:
+	test	r10b, r10b
+	jz	.quit
+	mov	rax, r8
+	.quit:
+	ret