Improve IAR construction
spot::iar() was fixed to handle correctly Rabin-like conditions. It also now supports Streett-like conditions. * NEWS, spot/twaalgos/postproc.cc: document it * spot/twaalgos/rabin2parity.cc, spot/twaalgos/rabin2parity.hh: implement it * tests/core/rabin2parity.test, tests/python/except.py: test it
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Maximilien Colange
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1ebd86de04
6 changed files with 103 additions and 33 deletions
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@ -242,10 +242,12 @@ namespace spot
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|| (want_parity && !a->acc().is_parity()))
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{
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twa_graph_ptr b = nullptr;
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if (want_parity && is_deterministic(a))
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if (want_parity && is_deterministic(a) &&
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!a->acc().is_generalized_buchi())
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b = iar_maybe(a);
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// possible only if a was deterministic and Rabin-like and
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// we want parity
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// possible only if a was deterministic and (Rabin-like or Streett-like)
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// and we want parity and a is not a TGBA
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// NB: on a TGBA, degeneralization is better than IAR
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if (b)
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a = b;
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else
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@ -21,7 +21,6 @@
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#include <spot/twaalgos/rabin2parity.hh>
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#include <spot/twaalgos/sccinfo.hh>
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#include <spot/twaalgos/isdet.hh>
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namespace spot
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{
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@ -41,8 +40,27 @@ namespace spot
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}
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};
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template<bool is_rabin>
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class iar_generator
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{
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// helper functions: access fin and inf parts of the pairs
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// these functions negate the Streett condition to see it as a Rabin one
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const acc_cond::mark_t&
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fin(unsigned k) const
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{
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if (is_rabin)
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return pairs_[k].fin;
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else
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return pairs_[k].inf;
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}
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acc_cond::mark_t
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inf(unsigned k) const
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{
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if (is_rabin)
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return pairs_[k].inf;
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else
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return pairs_[k].fin;
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}
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public:
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explicit iar_generator(const const_twa_graph_ptr& a,
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const std::vector<acc_cond::rs_pair>& p)
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@ -60,10 +78,14 @@ namespace spot
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build_iar_scc(scc_.initial());
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// resulting automaton has acceptance condition: parity max odd
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// with priorities ranging from 0 to 2*(nb Rabin pairs)
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// with priorities ranging from 0 to 2*(nb pairs)
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// /!\ priorities are shifted by -1 compared to the original paper
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res_->set_acceptance(2*pairs_.size() + 1,
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acc_cond::acc_code::parity(true, true, 2*pairs_.size() + 1));
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if (is_rabin)
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res_->set_acceptance(2*pairs_.size() + 1,
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acc_cond::acc_code::parity(true, true, 2*pairs_.size() + 1));
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else
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res_->set_acceptance(2*pairs_.size() + 1,
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acc_cond::acc_code::parity(true, false, 2*pairs_.size() + 1));
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// set initial state
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res_->set_init_state(
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@ -117,11 +139,11 @@ namespace spot
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return;
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}
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// determine the Rabin pairs that appear in the SCC
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// determine the pairs that appear in the SCC
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auto colors = scc_.acc_sets_of(scc_num);
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std::set<unsigned> scc_pairs;
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for (unsigned k = 0; k != pairs_.size(); ++k)
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if (colors & (pairs_[k].fin | pairs_[k].inf))
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if (inf(k) == 0U || (colors & (pairs_[k].fin | pairs_[k].inf)))
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scc_pairs.insert(k);
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perm_t p0;
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@ -150,10 +172,9 @@ namespace spot
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perm_t new_perm = current.perm;
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// Count pairs whose fin-part is seen on this transition
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unsigned seen_nb = 0;
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std::vector<unsigned> seen;
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// consider the pairs for this SCC only
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for (unsigned k : scc_pairs)
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if (e.acc & pairs_[k].fin)
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if (e.acc & fin(k))
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{
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++seen_nb;
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auto it = std::find(new_perm.begin(),
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@ -192,7 +213,8 @@ namespace spot
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for (unsigned k = 0; k != current.perm.size(); ++k)
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{
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unsigned pk = current.perm[k];
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if (e.acc & (pairs_[pk].fin | pairs_[pk].inf))
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if (inf(pk) == 0U ||
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(e.acc & (pairs_[pk].fin | pairs_[pk].inf)))
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// k increases in the loop, so k > maxint necessarily
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maxint = k;
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}
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@ -200,7 +222,7 @@ namespace spot
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acc_cond::mark_t acc = 0U;
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if (maxint == -1U)
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acc = {0};
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else if (e.acc & pairs_[current.perm[maxint]].fin)
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else if (e.acc & fin(current.perm[maxint]))
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acc = {2*maxint+2};
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else
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acc = {2*maxint+1};
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@ -271,12 +293,20 @@ namespace spot
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twa_graph_ptr
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iar_maybe(const const_twa_graph_ptr& aut)
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{
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std::vector<acc_cond::rs_pair> rabin_pairs;
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if (!aut->acc().is_rabin_like(rabin_pairs))
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return nullptr;
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iar_generator gen(aut, rabin_pairs);
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return gen.run();
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std::vector<acc_cond::rs_pair> pairs;
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if (!aut->acc().is_rabin_like(pairs))
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if (!aut->acc().is_streett_like(pairs))
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return nullptr;
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else
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{
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iar_generator<false> gen(aut, pairs);
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return gen.run();
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}
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else
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{
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iar_generator<true> gen(aut, pairs);
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return gen.run();
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}
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}
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twa_graph_ptr
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@ -284,6 +314,6 @@ namespace spot
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{
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if (auto res = iar_maybe(aut))
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return res;
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throw std::runtime_error("iar() expects Rabin-like input");
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throw std::runtime_error("iar() expects Rabin-like or Streett-like input");
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}
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}
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@ -23,30 +23,32 @@
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namespace spot
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{
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/// \ingroup twa_acc_transform
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/// \brief Turn a Rabin-like automaton into a parity automaton based on the
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/// index appearence record (IAR)
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/// \brief Turn a Rabin-like or Streett-like automaton into a parity automaton
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/// based on the index appearence record (IAR)
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///
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/// If the input automaton has n states and k pairs, the output automaton has
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/// at most k!*n states and 2k+1 colors. If the input automaton is
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/// deterministic, the output automaton is deterministic as well, which is the
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/// intended use case for this function. If the input automaton is
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/// non-deterministic, the result is still correct, but way larger than an
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/// equivalent Büchi automaton. The output parity automaton has max odd
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/// acceptance condition.
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/// equivalent Büchi automaton.
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/// If the input automaton is Rabin-like (resp. Streett-like), the output
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/// automaton has max odd (resp. min even) acceptance condition.
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/// Details on the algorithm can be found in:
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/// https://arxiv.org/pdf/1701.05738.pdf (published at TACAS 2017)
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///
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/// Throws an std::runtime_error if the input is not Rabin-like.
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/// Throws an std::runtime_error if the input is neither Rabin-like nor
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/// Street-like.
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SPOT_API
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twa_graph_ptr
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iar(const const_twa_graph_ptr& aut);
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/// \ingroup twa_acc_transform
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/// \brief Turn a Rabin-like automaton into a parity automaton based on the
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/// index appearence record (IAR)
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/// \brief Turn a Rabin-like or Streett-like automaton into a parity automaton
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/// based on the index appearence record (IAR)
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///
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/// Return nullptr if the input automaton is not Rabin-like, and
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/// calls spot::iar() otherwise.
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/// Returns nullptr if the input automaton is neither Rabin-like nor
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/// Streett-like, and calls spot::iar() otherwise.
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SPOT_API
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twa_graph_ptr
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iar_maybe(const const_twa_graph_ptr& aut);
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