// bump start to next page
		start = round(limit, pageSize)
	}
	return start, start + n
}

var memmap = mmap.Mmap
var munmap = mmap.Munmap

func (m *mappedFile) close() {
	m.closeOnce.Do(func() {
		if m.mapping != nil {
			munmap(m.mapping)
			m.mapping = nil
		}
		if m.f != nil {
			m.f.Close() // best effort
			m.f = nil
		}
	})
}

// IPv6 addresses.
func (ip Addr) Is6() bool {
	return ip.z != z0 && ip.z != z4
}

// Unmap returns ip with any IPv4-mapped IPv6 address prefix removed.
//
// That is, if ip is an IPv6 address wrapping an IPv4 address, it
// returns the wrapped IPv4 address. Otherwise it returns ip unmodified.
func (ip Addr) Unmap() Addr {
	if ip.Is4In6() {
		ip.z = z4
	}
	return ip
}

   * Compares strings in natural order except that null comes immediately before a given value. This
   * works better than Ordering.natural().nullsFirst() because, if null comes before all other
   * values, it lies outside the submap/submultiset ranges we test, and the variety of tests that
   * exercise null handling fail on those subcollections.
   */
  public abstract static class NullsBefore implements Comparator<@Nullable String>, Serializable {

	cachedSdom       SparseTree // cached dominator tree
	cachedLoopnest   *loopnest  // cached loop nest information
	cachedLineStarts *xposmap   // cached map/set of xpos to integers

	auxmap    auxmap             // map from aux values to opaque ids used by CSE
	constants map[int64][]*Value // constants cache, keyed by constant value; users must check value's Op and Type
}

type LocalSlotSplitKey struct {

   * Compares strings in natural order except that null comes immediately before a given value. This
   * works better than Ordering.natural().nullsFirst() because, if null comes before all other
   * values, it lies outside the submap/submultiset ranges we test, and the variety of tests that
   * exercise null handling fail on those subcollections.
   */
  public abstract static class NullsBefore implements Comparator<@Nullable String>, Serializable {