983964d037
Reported by Samuel Judson. * spot/twaalgos/strength.cc (is_safety_automaton): Reimplement it. * spot/twaalgos/strength.hh (is_safety_automaton): Update documentation. * tests/python/safety.py: New file. * tests/Makefile.am: Add it. * NEWS: Mention this change. * THANKS: Add Samuel.
210 lines
8.3 KiB
C++
210 lines
8.3 KiB
C++
// -*- coding: utf-8 -*-
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// Copyright (C) by the Spot authors, see the AUTHORS file for details.
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//
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// This file is part of Spot, a model checking library.
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//
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// Spot is free software; you can redistribute it and/or modify it
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// under the terms of the GNU General Public License as published by
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// the Free Software Foundation; either version 3 of the License, or
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// (at your option) any later version.
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//
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// Spot is distributed in the hope that it will be useful, but WITHOUT
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// ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
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// or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public
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// License for more details.
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//
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// You should have received a copy of the GNU General Public License
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// along with this program. If not, see <http://www.gnu.org/licenses/>.
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#pragma once
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#include <spot/twaalgos/sccinfo.hh>
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namespace spot
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{
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/// \brief Check whether an automaton is terminal.
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///
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/// An automaton is terminal if it is weak, all its accepting SCCs
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/// are complete, and no accepting SCC may lead to a non-accepting
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/// SCC.
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///
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/// This property guarantees that a word is accepted if it has some
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/// prefix that reaches an accepting transition.
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///
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/// \param aut the automaton to check
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///
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/// \param sm an scc_info object for the automaton if available (it
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/// will be built otherwise).
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///
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/// In addition to returning the result as a Boolean, this will set
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/// the prop_terminal() property of the automaton as a side-effect,
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/// so further calls will return in constant-time.
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SPOT_API bool
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is_terminal_automaton(const const_twa_graph_ptr& aut,
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scc_info* sm = nullptr);
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// 3-arg form was deprecated in Spot 2.12
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SPOT_DEPRECATED("is third argument of is_terminal_automaton()"
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" is now ignored")
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SPOT_API bool
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is_terminal_automaton(const const_twa_graph_ptr& aut,
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scc_info* sm, bool);
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/// \brief Check whether an automaton is weak.
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///
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/// An automaton is weak if in any given SCC, all transitions belong
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/// to the same acceptance sets.
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///
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/// \param aut the automaton to check
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///
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/// \param sm an scc_info object for the automaton if available (it
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/// will be built otherwise).
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///
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/// In addition to returning the result as a Boolean, this will set
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/// the prop_weak() property of the automaton as a side-effect,
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/// so further calls will return in constant-time.
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SPOT_API bool
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is_weak_automaton(const const_twa_graph_ptr& aut, scc_info* sm = nullptr);
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/// \brief Check whether an automaton is very-weak.
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///
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/// An automaton is very-weak if in any given SCC, all transitions
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/// belong to the same acceptance sets, and the SCC has only one
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/// state.
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///
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/// \param aut the automaton to check
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///
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/// \param sm an scc_info object for the automaton if available (it
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/// will be built otherwise).
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///
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/// In addition to returning the result as a Boolean, this will set
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/// the prop_very_weak() and prop_weak() properties of the automaton
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/// as a side-effect, so further calls will return in constant-time.
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SPOT_API bool
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is_very_weak_automaton(const const_twa_graph_ptr& aut,
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scc_info* sm = nullptr);
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/// \brief Check whether an automaton is inherently weak.
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///
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/// An automaton is inherently weak if in any given SCC, there
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/// are only accepting cycles, or only rejecting cycles.
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///
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/// \param aut the automaton to check
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///
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/// \param sm an scc_info object for the automaton if available (it
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/// will be built otherwise).
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///
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/// In addition to returning the result as a Boolean, this will set
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/// the prop_inherently_weak() property of the automaton as a
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/// side-effect, so further calls will return in constant-time.
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SPOT_API bool
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is_inherently_weak_automaton(const const_twa_graph_ptr& aut,
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scc_info* sm = nullptr);
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/// \brief Check whether an automaton is a safety automaton.
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///
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/// An automaton is a safety automaton if its acceptance condition
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/// can be changed to "true" without changing its language.
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///
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/// The test performed by this function differs depending on
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/// the nature of the input \a aut.
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///
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/// If \a aut is an automaton with `t` acceptance, it is necessarily
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/// a safety automaton.
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///
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/// Else we check for the absence of rejecting cycle in the
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/// useful part of the automaton. This absence is only a sufficient
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/// condition in the non-deterministic case, because a rejecting
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/// run might correspond to a word that is accepted by another run.
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///
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/// If the previous test could not conclude, we build the automaton
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/// B that is a copy of \a aut with acceptance set to true, and we
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/// check that \a aut contains all words of B. This last test
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/// requires complementing \a aut.
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///
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/// \param aut the automaton to check
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///
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/// \param sm an scc_info object for the automaton if available (it
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/// will be built otherwise).
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SPOT_API bool
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is_safety_automaton(const const_twa_graph_ptr& aut,
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scc_info* sm = nullptr);
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/// \brief Whether the automaton represents a liveness property.
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///
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/// An automaton represents a liveness property if after forcing the
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/// acceptance condition to true, the resulting automaton accepts
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/// all words. In other words, there is no prefix that cannot be
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/// extended into an accepting word.
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SPOT_API bool
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is_liveness_automaton(const const_twa_graph_ptr& aut);
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/// \brief Check whether an automaton is weak or terminal.
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///
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/// This sets the "inherently weak", "weak", "very-weak" and
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/// "terminal" properties as appropriate.
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///
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/// \param aut the automaton to check
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///
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/// \param sm an scc_info object for the automaton if available (it
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/// will be built otherwise).
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SPOT_API void
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check_strength(const twa_graph_ptr& aut, scc_info* sm = nullptr);
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/// \brief Extract a sub-automaton of a given strength
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///
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/// The string \a keep should be a non-empty combination of
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/// the following letters:
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/// - 'w': keep only inherently weak SCCs (i.e., SCCs in which
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/// all transitions belong to the same acceptance sets) that
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/// are not terminal.
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/// - 't': keep terminal SCCs (i.e., inherently weak SCCs that are complete)
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/// - 's': keep strong SCCs (i.e., SCCs that are not inherently weak).
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/// Additionally, the string may contain comma-separated numbers representing
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/// SCC number, optionally prefixed by 'a' to denote the Nth accepting SCC.
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///
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/// This algorithm returns a subautomaton that contains all SCCs of
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/// the requested strength (or given SCC numbers), plus any upstream
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/// SCC (but adjusted not to be accepting). The output may be null if
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/// no SCC match a given strength. An exception will be raised if
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/// an incorrect SCC number is supplied.
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///
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/// The definition are basically those used in the following paper,
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/// except that we extract the "inherently weak" part instead of the
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/// weak part because we can now test for inherent weakness
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/// efficiently enough (not enumerating all cycles as suggested in
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/// the paper). \cite renault.13.tacas
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///
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/// \param aut the automaton to decompose
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/// \param keep a string specifying the strengths/SCCs to keep
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SPOT_API twa_graph_ptr
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decompose_scc(const const_twa_graph_ptr& aut, const char* keep);
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/// \brief Extract a sub-automaton of a given strength
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///
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/// This works exactly like
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/// decompose_scc(const const_twa_graph_ptr&, const char*)
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/// but takes an \c scc_info as first argument. This avoids
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/// wasting time to reconstruct that object if one is already
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/// available.
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SPOT_API twa_graph_ptr
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decompose_scc(scc_info& sm, const char* keep);
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SPOT_DEPRECATED("use decompose_scc() instead")
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SPOT_API twa_graph_ptr
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decompose_strength(const const_twa_graph_ptr& aut, const char* keep);
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/// \brief Extract a sub-automaton above an SCC
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///
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/// This algorithm returns a subautomaton that contains the requested SCC,
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/// plus any upstream SCC (but adjusted not to be accepting).
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///
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/// \param sm the SCC info map of the automaton
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/// \param scc_num the index in the map of the SCC to keep
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/// \param accepting if true, scc_num is interpreted as the Nth
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/// accepting SCC instead of the Nth SCC
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SPOT_API twa_graph_ptr
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decompose_scc(scc_info& sm, unsigned scc_num, bool accepting = false);
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}
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