// authentication.
func UnixCredentials(ucred *Ucred) []byte {
	b := make([]byte, CmsgSpace(SizeofUcred))
	h := (*Cmsghdr)(unsafe.Pointer(&b[0]))
	h.Level = SOL_SOCKET
	h.Type = SCM_CREDENTIALS
	h.SetLen(CmsgLen(SizeofUcred))
	*(*Ucred)(h.data(0)) = *ucred
	return b
}

// ParseUnixCredentials decodes a socket control message that contains
// credentials in a Ucred structure. To receive such a message, the

func summary(list []*CommentGroup) string {
	const maxLen = 40
	var buf bytes.Buffer

	// collect comments text
loop:
	for _, group := range list {
		// Note: CommentGroup.Text() does too much work for what we
		//       need and would only replace this innermost loop.
		//       Just do it explicitly.
		for _, comment := range group.List {
			if buf.Len() >= maxLen {
				break loop
			}

	switch {
	case n == 0:
		return 0
	case n == 1:
		return IndexByte(s, substr[0])
	case n == len(s):
		if substr == s {
			return 0
		}
		return -1
	case n > len(s):
		return -1
	case n <= bytealg.MaxLen:
		// Use brute force when s and substr both are small
		if len(s) <= bytealg.MaxBruteForce {
			return bytealg.IndexString(s, substr)
		}
		c0 := substr[0]
		c1 := substr[1]
		i := 0
		t := len(s) - n + 1

	mc_es            uint16
	mc_ds            uint16
	mc_err           uint64
	mc_rip           uint64
	mc_cs            uint64
	mc_rflags        uint64
	mc_rsp           uint64
	mc_ss            uint64
	mc_len           uint64
	mc_fpformat      uint64
	mc_ownedfp       uint64
	mc_fpstate       [64]uint64
	mc_fsbase        uint64
	mc_gsbase        uint64
	mc_xfpustate     uint64
	mc_xfpustate_len uint64