//   The IANA has assigned the FC00::/7 prefix to "Unique Local Unicast".
	return len(ip) == IPv6len && ip[0]&0xfe == 0xfc
}

// IsMulticast reports whether ip is a multicast address.
func (ip IP) IsMulticast() bool {
	if ip4 := ip.To4(); ip4 != nil {
		return ip4[0]&0xf0 == 0xe0
	}
	return len(ip) == IPv6len && ip[0] == 0xff
}

// IsInterfaceLocalMulticast reports whether ip is

				case *syscall.SockaddrInet6:
					ifa := &IPNet{IP: make(IP, IPv6len), Mask: CIDRMask(int(puni.OnLinkPrefixLength), 8*IPv6len)}
					copy(ifa.IP, sa.Addr[:])
					ifat = append(ifat, ifa)
				}
			}
			for pany := aa.FirstAnycastAddress; pany != nil; pany = pany.Next {

				}
				stats.ipv4++
			}
			if ifa.IP.To16() != nil && ifa.IP.To4() == nil {
				if 0 >= prefixLen || prefixLen > 8*IPv6len || maxPrefixLen != 8*IPv6len {
					return nil, fmt.Errorf("unexpected prefix length: %d/%d for %#v", prefixLen, maxPrefixLen, ifa)
				}
				if ifa.IP.IsLoopback() && prefixLen != 8*IPv6len { // see RFC 4291
					return nil, fmt.Errorf("unexpected prefix length: %d/%d for %#v", prefixLen, maxPrefixLen, ifa)
				}

				continue NextVar
			}
		}
		out = append(out, inkv)
	}
	return out
}

const (
	IPv4len = 4
	IPv6len = 16
)

var v4InV6Prefix = []byte{0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0xff, 0xff}

func IPv4(a, b, c, d byte) IP {
	p := make(IP, IPv6len) // ERROR "make\(IP, 16\) escapes to heap"
	copy(p, v4InV6Prefix)
	p[12] = a
	p[13] = b
	p[14] = c
	p[15] = d
	return p
}

				continue
			}
			var ip IP
			switch sa := sa.(type) {
			case *syscall.SockaddrInet4:
				ip = IPv4(sa.Addr[0], sa.Addr[1], sa.Addr[2], sa.Addr[3])
			case *syscall.SockaddrInet6:
				ip = make(IP, IPv6len)
				copy(ip, sa.Addr[:])
				if ip[0] == 0xfe && ip[1] == 0xc0 {
					// fec0/10 IPv6 addresses are site local anycast DNS
					// addresses Microsoft sets by default if no other

			if ip.To4() != nil { // IPv4 or IPv6 IPv4-mapped address
				mask = CIDRMask(pfxlen-8*len(v4InV6Prefix), 8*IPv4len)
			}
			if ip.To16() != nil && ip.To4() == nil { // IPv6 address
				mask = CIDRMask(pfxlen, 8*IPv6len)
			}

			addrs = append(addrs, &IPNet{IP: ip, Mask: mask})
		}
	}

	return addrs, nil
}

// interfaceMulticastAddrTable returns addresses for a specific
// interface.

	testHookUninstaller.Do(uninstallTestHooks)

	b.Run("IPv4", func(b *testing.B) {
		benchmarkIPString(b, IPv4len)
	})

	b.Run("IPv6", func(b *testing.B) {
		benchmarkIPString(b, IPv6len)
	})
}

func benchmarkIPString(b *testing.B, size int) {
	b.ReportAllocs()
	b.ResetTimer()
	for i := 0; i < b.N; i++ {
		for _, tt := range ipStringTests {
			if tt.in != nil && len(tt.in) == size {

func ipv4only(addr IPAddr) bool {
	return addr.IP.To4() != nil
}

// ipv6only reports whether addr is an IPv6 address except IPv4-mapped IPv6 address.
func ipv6only(addr IPAddr) bool {
	return len(addr.IP) == IPv6len && addr.IP.To4() == nil
}

// SplitHostPort splits a network address of the form "host:port",
// "host%zone:port", "[host]:port" or "[host%zone]:port" into host or
// host%zone and port.
//

						}, c.PermittedURIDomains, c.ExcludedURIDomains); err != nil {
						return err
					}

				case nameTypeIP:
					ip := net.IP(data)
					if l := len(ip); l != net.IPv4len && l != net.IPv6len {
						return fmt.Errorf("x509: internal error: IP SAN %x failed to parse", data)
					}

					if err := c.checkNameConstraints(&comparisonCount, maxConstraintComparisons, "IP address", ip.String(), ip,

					return fmt.Errorf("x509: cannot parse URI %q: invalid domain", uriStr)
				}
			}
			uris = append(uris, uri)
		case nameTypeIP:
			switch len(data) {
			case net.IPv4len, net.IPv6len:
				ipAddresses = append(ipAddresses, data)
			default:
				return errors.New("x509: cannot parse IP address of length " + strconv.Itoa(len(data)))
			}
		}

		return nil
	})

	return
}