-#define SCM_VECTORP(x) (SCM_NIMP(x) && (SCM_TYP7S(x)==scm_tc7_vector))
-#define SCM_NVECTORP(x) (!SCM_VECTORP(x))
-#define SCM_VELTS(x) ((SCM *)SCM_CDR(x))
-#define SCM_SETVELTS SCM_SETCDR
+#define SCM_VECTORP(x) (SCM_NIMP (x) && (SCM_TYP7S (x) == scm_tc7_vector))
+#define SCM_VECTOR_BASE(x) ((scm_bits_t *) SCM_CELL_WORD_1 (x))
+#define SCM_SET_VECTOR_BASE(v, b) (SCM_SET_CELL_WORD_1 ((v), (b)))
+#define SCM_VECTOR_MAX_LENGTH ((1L << 24) - 1)
+#define SCM_VECTOR_LENGTH(x) (((unsigned long) SCM_CELL_WORD_0 (x)) >> 8)
+#define SCM_SET_VECTOR_LENGTH(v, l, t) (SCM_SET_CELL_WORD_0 ((v), ((l) << 8) + (t)))
+
+#define SCM_VELTS(x) ((SCM *) SCM_CELL_WORD_1 (x))
+#define SCM_VELTS_AS_STACKITEMS(x) ((SCM_STACKITEM *) SCM_CELL_WORD_1 (x))
+#define SCM_SETVELTS(x,v) (SCM_SET_CELL_WORD_1 ((x), (v)))
+