Add 'zdd_bot(...)' and 'zdd_top(...)'

This specifically is to address the suddenly missing feature with the prior
breaking change to 'zdd_powerset(...)' not being able to take the global domain
as an input. This is (arguably?) an even prettier solution.

src/adiar/zdd.h

@@ -257,6 +257,70 @@ namespace adiar
     return zdd_powerset(internal::iterator_gen<zdd::label_t>(begin, end));
   }
 
+  //////////////////////////////////////////////////////////////////////////////
+  /// \brief      Bottom of the powerset lattice.
+  ///
+  /// \param vars Generator function of the variables in *descending* order.
+  ///
+  /// \see zdd_empty
+  //////////////////////////////////////////////////////////////////////////////
+  inline zdd zdd_bot(const std::function<zdd::label_t()> &/*dom*/)
+  { return zdd_empty(); }
+
+  //////////////////////////////////////////////////////////////////////////////
+  /// \brief       Bottom of the powerset lattice.
+  ///
+  /// \param begin Iterator that provides the variables in *descending* order.
+  ///
+  /// \param end   Iterator that marks the end for `begin`.
+  ///
+  /// \see zdd_empty
+  //////////////////////////////////////////////////////////////////////////////
+  template<typename IT>
+  inline zdd zdd_bot(IT /*begin*/, IT /*end*/)
+  { return zdd_empty(); }
+
+  //////////////////////////////////////////////////////////////////////////////
+  /// \brief Bottom of the powerset lattice.
+  ///
+  /// \see zdd_empty
+  //////////////////////////////////////////////////////////////////////////////
+  inline zdd zdd_bot()
+  { return zdd_empty(); }
+
+  //////////////////////////////////////////////////////////////////////////////
+  /// \brief      Top of the powerset lattice.
+  ///
+  /// \param vars Generator function of the variables in *descending* order.
+  ///
+  /// \see zdd_powerset, zdd_null
+  //////////////////////////////////////////////////////////////////////////////
+  inline zdd zdd_top(const std::function<zdd::label_t()> &dom)
+  { return zdd_powerset(dom); }
+
+  //////////////////////////////////////////////////////////////////////////////
+  /// \brief       Top of the powerset lattice.
+  ///
+  /// \param begin Iterator that provides the variables in *descending* order.
+  ///
+  /// \param end   Iterator that marks the end for `begin`.
+  ///
+  /// \see zdd_empty
+  //////////////////////////////////////////////////////////////////////////////
+  template<typename IT>
+  inline zdd zdd_top(IT begin, IT end)
+  { return zdd_powerset(begin, end); }
+
+  //////////////////////////////////////////////////////////////////////////////
+  /// \brief   Top of the powerset lattice.
+  ///
+  /// \details Since no set of variables is given, the global \ref
+  ///          module__domain is used (if available).
+  ///
+  /// \see zdd_powerset, zdd_null
+  //////////////////////////////////////////////////////////////////////////////
+  zdd zdd_top();
+
   /// \}
   //////////////////////////////////////////////////////////////////////////////
 

src/adiar/zdd/build.cpp

@@ -135,4 +135,17 @@ namespace adiar
     internal::chain_both<zdd_policy> p;
     return internal::build_chain<>(p, vars);
   }
+
+  //////////////////////////////////////////////////////////////////////////////
+  zdd zdd_top()
+  {
+    if (!adiar_has_domain()) {
+      return zdd_null();
+    }
+
+    const shared_file<domain_var_t> dom = adiar_get_domain();
+    internal::file_stream<domain_var_t, true> ds(dom);
+
+    return zdd_powerset(internal::stream_gen<zdd::label_t>(ds));
+  }
 }