forth). A Go function called by C code may take C pointers as arguments,
and it may store non-pointer data, C pointers, or Go pointers to pinned
memory through those pointers. It may not store a Go pointer to unpinned
memory in memory pointed to by a C pointer (which again, implies that it
may not store a string, slice, channel, and so forth). A Go function
called by C code may take a Go pointer but it must preserve the property

	a := make([][]byte, len(spans))
	for i, span := range spans {
		a[i] = s[span.start:span.end:span.end]
	}

	return a
}

// Join concatenates the elements of s to create a new byte slice. The separator
// sep is placed between elements in the resulting slice.
func Join(s [][]byte, sep []byte) []byte {
	if len(s) == 0 {
		return []byte{}
	}
	if len(s) == 1 {
		// Just return a copy.

			spb = append(spb, zeroBlock[:pad]...)
			hdr.Size += int64(len(spb)) // Accounts for encoded sparse map

			// Add and modify appropriate PAX records.
			dir, file := path.Split(realName)
			hdr.Name = path.Join(dir, "GNUSparseFile.0", file)
			paxHdrs[paxGNUSparseMajor] = "1"
			paxHdrs[paxGNUSparseMinor] = "0"
			paxHdrs[paxGNUSparseName] = realName
			paxHdrs[paxGNUSparseRealSize] = strconv.FormatInt(realSize, 10)

	}
	in.expectNewline("#include")
	// Push tokenizer for file onto stack.
	fd, err := os.Open(name)
	if err != nil {
		for _, dir := range in.includes {
			fd, err = os.Open(filepath.Join(dir, name))
			if err == nil {
				break
			}
		}
		if err != nil {
			in.Error("#include:", err)
		}
	}
	in.Push(NewTokenizer(name, fd, fd))
}

// #line processing.

ahead of the loop in this program:
</p>

<pre>
n := 0
for e := list; e != nil; e = e.next {
	n++
}
i := *p
*q = 1
</pre>

<p>
If <code>list</code> pointed to a cyclic list,
then the original program would never access <code>*p</code> or <code>*q</code>,
but the rewritten program would.
(Moving `*p` ahead would be safe if the compiler can prove `*p` will not panic;