vs_sm_prev
int vs_sm_prev(SCR *, SMAP *, SMAP *);
if (vs_sm_prev(sp, p, p - 1)) {
if (vs_sm_prev(sp, p, p - 1)) {
if (vs_sm_prev(sp, &s1, &s2))
if (vs_sm_prev(sp, HMAP, HMAP))
if (vs_sm_prev(sp, HMAP + 1, HMAP))