OVFLSIZE
assert(FREESPACE(tp) >= OVFLSIZE);
FREESPACE(tp) = free_space - OVFLSIZE;
FREESPACE(tp) = free_space + OVFLSIZE;
sp[ndx + 3] = FREESPACE(sp) - OVFLSIZE;
(PAIRSIZE((K),(D)) + OVFLSIZE) <= FREESPACE((P)))