spot/spot/twaalgos/parity.cc

// -*- coding: utf-8 -*-
// Copyright (C) 2016, 2018 Laboratoire de Recherche et Développement
// de l'Epita (LRDE).
//
// This file is part of Spot, a model checking library.
//
// Spot is free software; you can redistribute it and/or modify it
// under the terms of the GNU General Public License as published by
// the Free Software Foundation; either version 3 of the License, or
// (at your option) any later version.
//
// Spot is distributed in the hope that it will be useful, but WITHOUT
// ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
// or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public
// License for more details.
//
// You should have received a copy of the GNU General Public License
// along with this program.  If not, see <http://www.gnu.org/licenses/>.

#include "config.h"
#include <spot/twaalgos/parity.hh>
#include <spot/twa/twagraph.hh>
#include <spot/twaalgos/product.hh>
#include <spot/twaalgos/complete.hh>
#include <vector>
#include <utility>
#include <functional>
#include <queue>

namespace spot
{
  namespace
  {
    unsigned change_set(unsigned x, unsigned num_sets,
                        bool change_kind, bool change_style)
    {
      // If the parity acceptance kind is changed,
      // then the index of the sets are reversed
      if (change_kind)
        x = num_sets - x - 1;
      // If the parity style is changed, then all the existing acceptance
      // sets are shifted
      x += change_style;
      return x;
    }

    void
    change_acc(twa_graph_ptr& aut, unsigned num_sets, bool change_kind,
               bool change_style, bool output_max, bool input_max)
    {
      for (auto& e: aut->edge_vector())
        if (e.acc)
          {
            unsigned msb = (input_max ? e.acc.max_set() : e.acc.min_set()) - 1;
            e.acc = acc_cond::mark_t{change_set(msb, num_sets, change_kind,
                                                change_style)};
          }
        else if (output_max && change_style)
          {
            // If the parity is changed, a new set is introduced.
            // This new set is used to mark all the transitions of the input
            // that don't belong to any acceptance sets.
            e.acc.set(0);
          }
    }

     [[noreturn]] static void
     input_is_not_parity(const char* fun)
     {
       throw std::runtime_error(std::string(fun) +
                                "(): input should have "
                                "parity acceptance");
     }
  }

  twa_graph_ptr
  change_parity(const const_twa_graph_ptr& aut,
                parity_kind kind, parity_style style)
  {
    return change_parity_here(make_twa_graph(aut, twa::prop_set::all()),
                              kind, style);
  }

  twa_graph_ptr
  change_parity_here(twa_graph_ptr aut, parity_kind kind, parity_style style)
  {
    bool current_max;
    bool current_odd;
    if (!aut->acc().is_parity(current_max, current_odd, true))
      input_is_not_parity("change_parity");
    auto old_num_sets = aut->num_sets();

    bool output_max = true;
    switch (kind)
      {
        case parity_kind_max:
          output_max = true;
          break;
        case parity_kind_min:
          output_max = false;
          break;
        case parity_kind_same:
          output_max = current_max;
          break;
        case parity_kind_any:
          // If we need to change the style we may change the kind not to
          // introduce new accset.
          output_max = (((style == parity_style_odd && !current_odd)
                         || (style == parity_style_even && current_odd))
                        && old_num_sets % 2 == 0) != current_max;
          break;
      }

    bool change_kind = current_max != output_max;
    bool toggle_style = change_kind && (old_num_sets % 2 == 0);

    bool output_odd = true;
    switch (style)
      {
        case parity_style_odd:
          output_odd = true;
          break;
        case parity_style_even:
          output_odd = false;
          break;
        case parity_style_same:
          output_odd = current_odd;
          break;
        case parity_style_any:
          output_odd = current_odd != toggle_style;
          // If we need to change the kind we may change the style not to
          // introduce new accset.
          break;
      }

    current_odd = current_odd != toggle_style;
    bool change_style = false;
    auto num_sets = old_num_sets;
    // If the parity neeeds to be changed, then a new acceptance set is created.
    // The old acceptance sets are shifted
    if (output_odd != current_odd)
      {
        change_style = true;
        ++num_sets;
      }

    if (change_kind || change_style)
      {
        auto new_acc = acc_cond::acc_code::parity(output_max,
                                                  output_odd, num_sets);
        aut->set_acceptance(num_sets, new_acc);
      }
    change_acc(aut, old_num_sets, change_kind,
               change_style, output_max, current_max);
    return aut;
  }

  twa_graph_ptr
  cleanup_parity(const const_twa_graph_ptr& aut, bool keep_style)
  {
    auto result = make_twa_graph(aut, twa::prop_set::all());
    return cleanup_parity_here(result, keep_style);
  }

  twa_graph_ptr
  cleanup_parity_here(twa_graph_ptr aut, bool keep_style)
  {
    bool current_max;
    bool current_odd;
    if (!aut->acc().is_parity(current_max, current_odd, true))
      input_is_not_parity("cleanup_parity");
    auto num_sets = aut->num_sets();
    if (num_sets == 0)
      return aut;

    // Compute all the used sets
    auto used_in_aut = acc_cond::mark_t();
    for (auto& t: aut->edges())
      {
        // leave only one color on each transition
        if (current_max)
          {
            auto maxset = t.acc.max_set();
            if (maxset)
              t.acc = acc_cond::mark_t{maxset - 1};
          }
        else
          {
            t.acc = t.acc.lowest();
          }
        // recall colors used in the automaton
        used_in_aut |= t.acc;
      }

    // remove from the acceptance condition the unused one (starting from the
    // least significant)
    auto useful = used_in_aut;
    int useful_min = 0;
    int useful_max = num_sets-1;
    if (!current_max)
      {
        int n = num_sets-1;
        while (n >= 0 && !useful.has(n))
          {
            if (n > 0)
              useful.clear(n-1);
            n -= 2;
          }
        useful_max = n;
      }
    else
      {
        unsigned n = 0;
        while (n < num_sets && !useful.has(n))
          {
            useful.clear(n+1);
            n += 2;
          }
        useful_min = n;
      }
    if (used_in_aut)
    {
      // Never remove the least significant acceptance set, and mark the
      // acceptance set 0 to keep the style if needed.
      if (keep_style && useful_min <= useful_max)
        {
          useful.set(useful_min);
          useful.set(useful_max);
        }

      // Fill the vector shift with the new acceptance sets
      std::vector<unsigned> shift(num_sets);
      int prev_used = -1;
      bool change_style = false;
      unsigned new_index = 0;
      for (auto i = 0U; i < num_sets; ++i)
        if (useful.has(i))
          {
            if (prev_used == -1)
              change_style = i % 2 != 0;
            else if ((i + prev_used) % 2 != 0)
              ++new_index;
            shift[i] = new_index;
            prev_used = i;
          }

      // Update all the transitions with the vector shift
      for (auto& t: aut->edges())
        {
          t.acc &= useful;
          auto maxset = t.acc.max_set();
          if (maxset)
            t.acc = acc_cond::mark_t{shift[maxset - 1]};
        }

      auto new_num_sets = new_index + 1;
      if (!useful)
        {
          new_num_sets = 0;
          if (current_max)
            change_style = false;
          else
            change_style = num_sets % 2 == 1;
        }

      if (new_num_sets < num_sets)
        {
          auto new_acc =
            acc_cond::acc_code::parity(current_max,
                                       current_odd != change_style,
                                       new_num_sets);
          aut->set_acceptance(new_num_sets, new_acc);
        }
    }
    else
      {
        if ((current_max && current_odd)
           || (!current_max && current_odd != (num_sets % 2 == 0)))
          aut->set_acceptance(0, acc_cond::acc_code::t());
        else
          aut->set_acceptance(0, acc_cond::acc_code::f());
      }
    return aut;
  }

  twa_graph_ptr
  colorize_parity(const const_twa_graph_ptr& aut, bool keep_style)
  {
    return colorize_parity_here(make_twa_graph(aut, twa::prop_set::all()),
                                keep_style);
  }

  twa_graph_ptr
  colorize_parity_here(twa_graph_ptr aut, bool keep_style)
  {
    bool current_max;
    bool current_odd;
    if (!aut->acc().is_parity(current_max, current_odd, true))
      input_is_not_parity("colorize_parity");

    bool has_empty = false;
    for (const auto& e: aut->edges())
      if (!e.acc)
        {
          has_empty = true;
          break;
        }
    auto num_sets = aut->num_sets();
    int incr = 0;
    if (has_empty)
      {
        // If the automaton has a transition that belong to any set, we need to
        // introduce a new acceptance set.
        // We may want to add a second acceptance set to keep the style of
        // the parity acceptance
        incr = 1 + (keep_style && current_max);
        num_sets += incr;
        bool new_style = current_odd == (keep_style || !current_max);
        auto new_acc = acc_cond::acc_code::parity(current_max,
                                                  new_style, num_sets);
        aut->set_acceptance(num_sets, new_acc);
      }
    if (current_max)
      {
        --incr;
        for (auto& e: aut->edges())
          {
            auto maxset = e.acc.max_set();
            e.acc = acc_cond::mark_t{maxset ? maxset + incr : incr};
          }
      }
    else
      {
        auto unused_mark = num_sets - incr;
        for (auto& e: aut->edges())
          e.acc = e.acc ? e.acc.lowest() : acc_cond::mark_t{unused_mark};
      }
    return aut;
  }

}