wnd_is_free_hlp
while (bit > ib && wnd_is_free_hlp(wnd, bit - 1, 1)) {
while (end_in < ib && wnd_is_free_hlp(wnd, end_in, 1)) {
static bool wnd_is_free_hlp(struct wnd_bitmap *wnd, size_t bit, size_t bits);
ret = wnd_is_free_hlp(wnd, bit, bits);