[libc] optimize strnlen and add strlen

src/libc/os.src

@@ -24,8 +24,6 @@ _strcmp     := 0000C8h
 _strcpy     := 0000CCh
 	public	_strcspn
 _strcspn    := 0000D0h
-	public	_strlen
-_strlen     := 0000D4h
 	public	_strncat
 _strncat    := 0000D8h
 	public	_strncmp

src/libc/strlen.src

@@ -0,0 +1,26 @@
+	assume	adl=1
+
+	section	.text
+	public	_strlen
+
+if PREFER_OS_LIBC
+
+_strlen := $0000D4
+
+else
+
+_strlen:
+	pop	de
+	ex	(sp),hl
+	push	de
+	push	hl
+	pop	de
+	xor	a,a
+	ld	bc,0
+	cpir
+	scf
+	sbc	hl,de
+	ret
+
+end if
+

src/libc/strnlen.src

@@ -3,27 +3,13 @@
 	section	.text
 	public	_strnlen
 _strnlen:
-	call	__frameset0
-	ld	de,(ix+6)
-	ld	bc,(ix+9)
-	or	a,a
-	sbc	hl,hl
-	jr	StartFor
-ForLoop:
-	inc	hl
-	inc	de
-StartFor:
-	push	hl
-	or	a,a
-	sbc	hl,bc
+	pop	hl,de,bc
+	push	bc,de,hl
+	push	de
 	pop	hl
-	jr	nc,ReachedMax
-	ld	a,(de)
-	or	a,a
-	jr	nz,ForLoop
-ReachedMax:
-	ld	sp,ix
-	pop	ix
+	xor	a,a
+	inc	bc
+	cpir
+	scf
+	sbc	hl,de
 	ret
-
-	extern	__frameset0