Adds strcat()

src/string.asm

@@ -3,6 +3,7 @@
 section .text
 	global	strlen
 	global	strcpy
+	global	strcat
 
 ;----- strlen(*str[]) -----;
 ; Gets the length of given string
@@ -24,7 +25,7 @@ strlen:
 ;----- strcpy(*dest[], *src[], maxLength) -----;
 ; Copies one string (src) into the other (dest), overwriting dest
 ; NOTE: maxLength must never exceed size of dest[]. 
-; Return value: Pointer to dest
+; Return value: Pointer to dest[]
 ; Used registers:
 ;	rax*	(ret) Pointer to dest[]
 ;	rdi*	(arg) Pointer to dest[]
@@ -43,9 +44,48 @@ strcpy:
 	cmp	rcx, rdx
 	jb	.copy
 	dec	rcx
-	.copy
+	.copy:
 	mov	rdi, r8
 	rep	movsb
 	mov	byte [rdi], EOS
 	mov	rax, r8
 	ret
+
+;----- strcat(*dest[], *src[], maxLength) -----;
+; Concatenate src[] into dest[]
+; Return value: Pointer to dest[]
+; Used registers:
+;	rax*	(ret) Pointer to dest[]
+;	rdi*	(arg) Pointer to dest[]
+;	rsi*	(arg) Pointer to src[]
+;	rdx	(arg) Size of dest[]
+;	rcx*	Counter for movsb
+;	r8*	Backup for rdi
+;	r9*	Backup for rsi
+;	r10*	Current length of dest[]
+strcat:
+	mov	r8, rdi
+	mov	r9, rsi
+	mov	rdi, rsi
+	call	strlen ;16
+	mov	rcx, rax
+	mov	rdi, r8
+	call	strlen ;20
+	mov	r10, rax
+	mov	rdi, r8
+	add	rcx, rax ;36
+	cmp	rcx, rdx ;36 <> 32
+	cmova	rcx, rdx
+	cmp	rcx, rdx
+	jb	.copy
+	dec	rcx
+	.copy:	
+	mov	rdi, r8
+	mov	rsi, r9
+	add	rdi, r10
+	sub	rcx, r10
+	cld
+	rep	movsb
+	mov	byte [rdi], EOS
+	mov	rax, r8
+	ret