Add commit 43aab01 of BenHanson/lexertl14 from github

YACReaderLibrary/lexertl/partition/charset.hpp

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+// charset.hpp
+// Copyright (c) 2005-2018 Ben Hanson (http://www.benhanson.net/)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file licence_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+
+#ifndef LEXERTL_CHARSET_HPP
+#define LEXERTL_CHARSET_HPP
+
+#include <algorithm>
+#include <iterator>
+#include <set>
+#include "../string_token.hpp"
+
+namespace lexertl
+{
+namespace detail
+{
+template<typename char_type, typename id_type>
+struct basic_charset
+{
+    using token = basic_string_token<char_type>;
+    using index_set = std::set<id_type>;
+
+    token _token;
+    index_set _index_set;
+
+    basic_charset() :
+        _token(),
+        _index_set()
+    {
+    }
+
+    basic_charset(const token &token_, const id_type index_) :
+        _token(token_),
+        _index_set()
+    {
+        _index_set.insert(index_);
+    }
+
+    bool empty() const
+    {
+        return _token.empty() && _index_set.empty();
+    }
+
+    void intersect(basic_charset &rhs_, basic_charset &overlap_)
+    {
+        _token.intersect(rhs_._token, overlap_._token);
+
+        if (!overlap_._token.empty())
+        {
+            std::merge(_index_set.begin(), _index_set.end(),
+                rhs_._index_set.begin(), rhs_._index_set.end(),
+                std::inserter(overlap_._index_set,
+                overlap_._index_set.end()));
+
+            if (_token.empty())
+            {
+                _index_set.clear();
+            }
+
+            if (rhs_._token.empty())
+            {
+                rhs_._index_set.clear();
+            }
+        }
+    }
+};
+}
+}
+
+#endif