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

NEWS

@@ -1,11 +1,17 @@
 New in spot 2.5.0.dev (not yet released)
 
+  Library:
+
+  - iar() and iar_maybe() now also handle Streett-like conditions.
+
   Bugs fixed:
 
   - streett_to_generalized_buchi() could produce incorrect result on
     Streett-like input with acceptance like (Inf(0)|Fin(1))&Fin(1)
     where some Fin(x) is used both with and without a paired Fin(y).
 
+  - iar() and iar_maybe() properly handle Rabin-like conditions.
+
 New in spot 2.5 (2018-01-20)
 
   Build:
@@ -92,7 +98,7 @@ New in spot 2.5 (2018-01-20)
   New functions in the library:
 
   - spot::iar() and spot::iar_maybe() use index appearance records (IAR)
-    to translate Rabin-like automata into equivalent parity automaton.
+    to translate Rabin-like automata into equivalent parity automata.
     This translation preserves determinism and is especially useful when
     the input automaton is deterministic.
 

spot/twaalgos/postproc.cc

@@ -242,10 +242,12 @@ namespace spot
         || (want_parity && !a->acc().is_parity()))
       {
         twa_graph_ptr b = nullptr;
-        if (want_parity && is_deterministic(a))
+        if (want_parity && is_deterministic(a) &&
+            !a->acc().is_generalized_buchi())
           b = iar_maybe(a);
-        // possible only if a was deterministic and Rabin-like and
+        // possible only if a was deterministic and (Rabin-like or Streett-like)
-        // we want parity
+        // and we want parity and a is not a TGBA
+        // NB: on a TGBA, degeneralization is better than IAR
         if (b)
           a = b;
         else

spot/twaalgos/rabin2parity.cc

@@ -21,7 +21,6 @@
 #include <spot/twaalgos/rabin2parity.hh>
 
 #include <spot/twaalgos/sccinfo.hh>
-#include <spot/twaalgos/isdet.hh>
 
 namespace spot
 {
@@ -41,8 +40,27 @@ namespace spot
       }
     };
 
+    template<bool is_rabin>
     class iar_generator
     {
+      // helper functions: access fin and inf parts of the pairs
+      // these functions negate the Streett condition to see it as a Rabin one
+      const acc_cond::mark_t&
+      fin(unsigned k) const
+      {
+        if (is_rabin)
+          return pairs_[k].fin;
+        else
+          return pairs_[k].inf;
+      }
+      acc_cond::mark_t
+      inf(unsigned k) const
+      {
+        if (is_rabin)
+          return pairs_[k].inf;
+        else
+          return pairs_[k].fin;
+      }
     public:
       explicit iar_generator(const const_twa_graph_ptr& a,
                              const std::vector<acc_cond::rs_pair>& p)
@@ -60,10 +78,14 @@ namespace spot
         build_iar_scc(scc_.initial());
 
         // resulting automaton has acceptance condition: parity max odd
-        // with priorities ranging from 0 to 2*(nb Rabin pairs)
+        // with priorities ranging from 0 to 2*(nb pairs)
         // /!\ priorities are shifted by -1 compared to the original paper
+        if (is_rabin)
           res_->set_acceptance(2*pairs_.size() + 1,
               acc_cond::acc_code::parity(true, true, 2*pairs_.size() + 1));
+        else
+          res_->set_acceptance(2*pairs_.size() + 1,
+              acc_cond::acc_code::parity(true, false, 2*pairs_.size() + 1));
 
         // set initial state
         res_->set_init_state(
@@ -117,11 +139,11 @@ namespace spot
             return;
           }
 
-        // determine the Rabin pairs that appear in the SCC
+        // determine the pairs that appear in the SCC
         auto colors = scc_.acc_sets_of(scc_num);
         std::set<unsigned> scc_pairs;
         for (unsigned k = 0; k != pairs_.size(); ++k)
-          if (colors & (pairs_[k].fin | pairs_[k].inf))
+          if (inf(k) == 0U || (colors & (pairs_[k].fin | pairs_[k].inf)))
             scc_pairs.insert(k);
 
         perm_t p0;
@@ -150,10 +172,9 @@ namespace spot
                     perm_t new_perm = current.perm;
                     // Count pairs whose fin-part is seen on this transition
                     unsigned seen_nb = 0;
-                    std::vector<unsigned> seen;
                     // consider the pairs for this SCC only
                     for (unsigned k : scc_pairs)
-                      if (e.acc & pairs_[k].fin)
+                      if (e.acc & fin(k))
                         {
                           ++seen_nb;
                           auto it = std::find(new_perm.begin(),
@@ -192,7 +213,8 @@ namespace spot
                     for (unsigned k = 0; k != current.perm.size(); ++k)
                       {
                         unsigned pk = current.perm[k];
-                        if (e.acc & (pairs_[pk].fin | pairs_[pk].inf))
+                        if (inf(pk) == 0U ||
+                            (e.acc & (pairs_[pk].fin | pairs_[pk].inf)))
                           // k increases in the loop, so k > maxint necessarily
                           maxint = k;
                       }
@@ -200,7 +222,7 @@ namespace spot
                     acc_cond::mark_t acc = 0U;
                     if (maxint == -1U)
                       acc = {0};
-                    else if (e.acc & pairs_[current.perm[maxint]].fin)
+                    else if (e.acc & fin(current.perm[maxint]))
                       acc = {2*maxint+2};
                     else
                       acc = {2*maxint+1};
@@ -271,19 +293,27 @@ namespace spot
   twa_graph_ptr
   iar_maybe(const const_twa_graph_ptr& aut)
   {
-    std::vector<acc_cond::rs_pair> rabin_pairs;
+    std::vector<acc_cond::rs_pair> pairs;
-    if (!aut->acc().is_rabin_like(rabin_pairs))
+    if (!aut->acc().is_rabin_like(pairs))
+      if (!aut->acc().is_streett_like(pairs))
         return nullptr;
-
+      else
-    iar_generator gen(aut, rabin_pairs);
+        {
+          iar_generator<false> gen(aut, pairs);
           return gen.run();
         }
+    else
+      {
+        iar_generator<true> gen(aut, pairs);
+        return gen.run();
+      }
+  }
 
   twa_graph_ptr
   iar(const const_twa_graph_ptr& aut)
   {
     if (auto res = iar_maybe(aut))
       return res;
-    throw std::runtime_error("iar() expects Rabin-like input");
+    throw std::runtime_error("iar() expects Rabin-like or Streett-like input");
   }
 }

spot/twaalgos/rabin2parity.hh

@@ -23,30 +23,32 @@
 namespace spot
 {
   /// \ingroup twa_acc_transform
-  /// \brief Turn a Rabin-like automaton into a parity automaton based on the
+  /// \brief Turn a Rabin-like or Streett-like automaton into a parity automaton
-  /// index appearence record (IAR)
+  /// based on the index appearence record (IAR)
   ///
   /// If the input automaton has n states and k pairs, the output automaton has
   /// at most k!*n states and 2k+1 colors. If the input automaton is
   /// deterministic, the output automaton is deterministic as well, which is the
   /// intended use case for this function. If the input automaton is
   /// non-deterministic, the result is still correct, but way larger than an
-  /// equivalent Büchi automaton. The output parity automaton has max odd
+  /// equivalent Büchi automaton.
-  /// acceptance condition.
+  /// If the input automaton is Rabin-like (resp. Streett-like), the output
+  /// automaton has max odd (resp. min even) acceptance condition.
   /// Details on the algorithm can be found in:
   ///   https://arxiv.org/pdf/1701.05738.pdf (published at TACAS 2017)
   ///
-  /// Throws an std::runtime_error if the input is not Rabin-like.
+  /// Throws an std::runtime_error if the input is neither Rabin-like nor
+  /// Street-like.
   SPOT_API
   twa_graph_ptr
   iar(const const_twa_graph_ptr& aut);
 
   /// \ingroup twa_acc_transform
-  /// \brief Turn a Rabin-like automaton into a parity automaton based on the
+  /// \brief Turn a Rabin-like or Streett-like automaton into a parity automaton
-  /// index appearence record (IAR)
+  /// based on the index appearence record (IAR)
   ///
-  /// Return nullptr if the input automaton is not Rabin-like, and
+  /// Returns nullptr if the input automaton is neither Rabin-like nor
-  /// calls spot::iar() otherwise.
+  /// Streett-like, and calls spot::iar() otherwise.
   SPOT_API
   twa_graph_ptr
   iar_maybe(const const_twa_graph_ptr& aut);

tests/core/rabin2parity.test

@@ -1,6 +1,6 @@
 #!/bin/sh
 # -*- coding: utf-8 -*-
-# Copyright (C) 2017 Laboratoire de Recherche et
+# Copyright (C) 2017-2018 Laboratoire de Recherche et
 # Développement de l'Epita (LRDE).
 #
 # This file is part of Spot, a model checking library.
@@ -39,9 +39,39 @@ State: 1
 [0] 1 {1 }
 [!0] 1 {0 1 }
 --END--
+HOA: v1
+States: 1
+Start: 0
+AP: 1 "a"
+acc-name: Streett 1
+Acceptance: 2 Fin(0) | Inf(1)
+properties: trans-labels explicit-labels state-acc complete
+properties: deterministic
+--BODY--
+State: 0
+[t] 0
+--END--
+HOA: v1
+States: 3
+Start: 0
+AP: 1 "a"
+acc-name: Streett 3
+Acceptance: 6 (Fin(0) | Inf(1)) & (Fin(2) | Inf(3)) & (Fin(4) | Inf(5))
+properties: trans-labels explicit-labels trans-acc deterministic
+--BODY--
+State: 0
+[!0] 0 {1 3}
+[0] 1 {}
+State: 1
+[0] 2 {2}
+State: 2
+[!0] 0 {0 4}
+[0] 2 {}
+--END--
 EOF
 # random automata
-randaut 5 -n100 -u -D --acceptance="Rabin 0..6"
+randaut 4 -n100 -u -D --acceptance="Rabin 0..6"
+randaut 4 -n100 -u -D --acceptance="Streett 0..6"
 ) | \
 autcross \
   "autfilt --parity" \

tests/python/except.py

@@ -27,7 +27,7 @@ import spot
 try:
     spot.iar(spot.translate('GFa & GFb & GFc'))
 except RuntimeError as e:
-    assert 'iar() expects Rabin-like input' in str(e)
+    assert 'iar() expects Rabin-like or Streett-like input' in str(e)
 
 alt = spot.dualize(spot.translate('FGa | FGb'))