diff --git a/libsrc/atari/mul40.s b/libsrc/atari/mul40.s
new file mode 100644
index 000000000..b14d960a0
--- /dev/null
+++ b/libsrc/atari/mul40.s
@@ -0,0 +1,35 @@
+;
+; Christian Groessler, June 2000
+;
+; mul40
+; multiplies A by 40 and returns result in AX
+; uses tmp4
+
+	.importzp	tmp4
+	.export		mul40
+
+.proc	mul40
+
+	ldx	#0
+	stx	tmp4
+	sta	loc_tmp
+	asl	a
+	rol	tmp4
+	asl	a
+	rol	tmp4		; val * 4
+	adc	loc_tmp
+	bcc	L1
+	inc	tmp4		; val * 5
+L1:	asl	a
+	rol	tmp4		; val * 10
+	asl	a
+	rol	tmp4
+	asl	a
+	rol	tmp4		; val * 40
+	ldx	tmp4
+	rts
+
+.endproc
+
+	.bss
+loc_tmp:.res	1