// building. They are used to mark duplicate entries.
		files := make(map[string]int)
		knownDirs := make(map[string]int)

		// dirs[name] is true if name is known to be a directory,
		// because it appears as a prefix in a path.
		dirs := make(map[string]bool)

		for _, file := range r.File {
			isDir := len(file.Name) > 0 && file.Name[len(file.Name)-1] == '/'
			name := toValidName(file.Name)

			if b := gnu.changeTime(); b[0] != 0 {
				hdr.ChangeTime = time.Unix(p2.parseNumeric(b), 0)
			}

			// Prior to Go1.8, the Writer had a bug where it would output
			// an invalid tar file in certain rare situations because the logic
			// incorrectly believed that the old GNU format had a prefix field.
			// This is wrong and leads to an output file that mangles the
			// atime and ctime fields, which are often left unused.
			//