diff --git a/ueforth/common/calling.h b/ueforth/common/calling.h
new file mode 100644
index 0000000..3c06d0f
--- /dev/null
+++ b/ueforth/common/calling.h
@@ -0,0 +1,32 @@
+#define SET tos = (cell_t)
+
+#define n0 tos
+#define n1 (*sp)
+#define n2 sp[-1]
+#define n3 sp[-2]
+#define n4 sp[-3]
+#define n5 sp[-4]
+#define n6 sp[-5]
+#define n7 sp[-6]
+#define n8 sp[-7]
+#define n9 sp[-8]
+#define n10 sp[-9]
+
+#define a0 ((void *) tos)
+#define a1 (*(void **) &n1)
+#define a2 (*(void **) &n2)
+#define a3 (*(void **) &n3)
+#define a4 (*(void **) &n4)
+
+#define b0 ((uint8_t *) tos)
+#define b1 (*(uint8_t **) &n1)
+#define b2 (*(uint8_t **) &n2)
+#define b3 (*(uint8_t **) &n3)
+#define b4 (*(uint8_t **) &n4)
+
+#define c0 ((char *) tos)
+#define c1 (*(char **) &n1)
+#define c2 (*(char **) &n2)
+#define c3 (*(char **) &n3)
+#define c4 (*(char **) &n4)
+