autfilt: Add '--decompose-scc' option

See #172.

* bin/autfilt.cc: Add option.
* tests/core/strength.test: Remove ambiguity with
'--decompose-strength'.
* NEWS: Mention it.
* tests/core/scc.test: Test it.

NEWS

@@ -21,6 +21,11 @@ New in spot 2.3.1 (2017-02-20)
     Kupferman & Rosenberg [MoChArt'10] are recognizable by
     deterministic Büchi automata with at least 2^2^n states.
 
+  - autfilt has a new transformation: --decompose-scc, which allows
+    decomposition of automata through their accepting SCCs.
+    A demonstration of this feature via the Python bindings
+    can be found at https://spot.lrde.epita.fr/ipynb/decompose.html
+
   Library:
 
   - spot::twa_run::as_twa() has an option to preserve state names.

bin/autfilt.cc

@@ -88,6 +88,7 @@ enum {
   OPT_COMPLEMENT_ACC,
   OPT_COUNT,
   OPT_DECOMPOSE_STRENGTH,
+  OPT_DECOMPOSE_SCC,
   OPT_DESTUT,
   OPT_DNF_ACC,
   OPT_EDGES,
@@ -295,6 +296,8 @@ static const argp_option options[] =
     { "decompose-strength", OPT_DECOMPOSE_STRENGTH, "t|w|s", 0,
       "extract the (t) terminal, (w) weak, or (s) strong part of an automaton"
       " (letters may be combined to combine more strengths in the output)", 0 },
+    { "decompose-scc", OPT_DECOMPOSE_SCC, "N", 0, "keep only the Nth accepting"
+      " SCC as accepting", 0 },
     { "exclusive-ap", OPT_EXCLUSIVE_AP, "AP,AP,...", 0,
       "if any of those APs occur in the automaton, restrict all edges to "
       "ensure two of them may not be true at the same time.  Use this option "
@@ -469,6 +472,7 @@ static bool opt_clean_acc = false;
 static bool opt_complement = false;
 static bool opt_complement_acc = false;
 static char* opt_decompose_strength = nullptr;
+static int opt_decompose_scc = -1;
 static spot::acc_cond::mark_t opt_mask_acc = 0U;
 static std::vector<bool> opt_keep_states = {};
 static unsigned int opt_keep_states_initial = 0;
@@ -564,6 +568,9 @@ parse_opt(int key, char* arg, struct argp_state*)
     case OPT_DECOMPOSE_STRENGTH:
       opt_decompose_strength = arg;
       break;
+    case OPT_DECOMPOSE_SCC:
+      opt_decompose_scc = to_pos_int(arg);
+      break;
     case OPT_DESTUT:
       opt_destut = true;
       break;
@@ -1188,6 +1195,26 @@ namespace
             return 0;
         }
 
+      if (opt_decompose_scc != -1)
+        {
+          spot::scc_info si(aut);
+          unsigned scc_num = 0;
+
+          for (; scc_num < si.scc_count(); ++scc_num)
+            {
+              if (si.is_accepting_scc(scc_num))
+                {
+                  if (!opt_decompose_scc)
+                    break;
+                  --opt_decompose_scc;
+                }
+            }
+
+          aut = decompose_scc(si, scc_num);
+          if (!aut)
+            return 0;
+        }
+
       if (opt_sat_minimize)
         {
           aut = spot::sat_minimize(aut, opt_sat_minimize, sbacc);

tests/core/scc.test

 #!/bin/sh
 # -*- coding: utf-8 -*-
-# Copyright (C) 2009, 2015 Laboratoire de Recherche et Developpement de
+# Copyright (C) 2009, 2015, 2017 Laboratoire de Recherche et Developpement de
 # l'Epita
 #
 # This file is part of Spot, a model checking library.
@@ -33,3 +33,73 @@ EOF
 run 0 ltl2tgba --low --any --stats='%f,%e,%s,%c' -F formulas/1 >out
 cat out
 diff out formulas
+
+ltl2tgba 'a W b' > aut
+
+cat >ref<<EOF
+HOA: v1
+States: 2
+Start: 0
+AP: 2 "a" "b"
+acc-name: Buchi
+Acceptance: 1 Inf(0)
+properties: trans-labels explicit-labels state-acc deterministic
+--BODY--
+State: 0
+[1] 1
+[0&!1] 0
+State: 1 {0}
+[t] 1
+--END--
+EOF
+
+run 0 autfilt --decompose-scc=0 -F aut> out
+cat out
+diff out ref
+
+cat >ref<<EOF
+HOA: v1
+States: 1
+Start: 0
+AP: 2 "a" "b"
+acc-name: Buchi
+Acceptance: 1 Inf(0)
+properties: trans-labels explicit-labels state-acc colored
+properties: deterministic
+--BODY--
+State: 0 {0}
+[0&!1] 0
+--END--
+EOF
+
+run 0 autfilt --decompose-scc=1 -F aut> out
+cat out
+diff out ref
+
+autfilt --decompose-scc=2 -F aut 2>stderr && exit 1
+[ $? -eq 2 ]
+grep "out of bounds" stderr
+
+# always satisfied acceptance
+ltl2tgba 'Ga R b | Gc R b' > aut
+
+cat >ref<<EOF
+HOA: v1
+States: 2
+Start: 0
+AP: 3 "b" "a" "c"
+acc-name: Buchi
+Acceptance: 1 Inf(0)
+properties: trans-labels explicit-labels state-acc
+--BODY--
+State: 0
+[0&2] 1
+[0] 0
+State: 1 {0}
+[2] 1
+--END--
+EOF
+
+run 0 autfilt --decompose-scc=1 -F aut> out
+cat out
+diff out ref

tests/core/strength.test

 #!/bin/sh
 # -*- coding: utf-8 -*-
-# Copyright (C) 2015, 2016 Laboratoire de Recherche et Developpement
+# Copyright (C) 2015, 2016, 2017 Laboratoire de Recherche et Developpement
 # de l'Epita
 #
 # This file is part of Spot, a model checking library.
@@ -221,12 +221,12 @@ EOF
 diff out expected
 
 
-run 0 $autfilt -H --decompose=t in | tee out.t
-run 0 $autfilt -H --decompose=w in | tee out.w
-run 0 $autfilt -H --decompose=s in | tee out.s
-run 0 $autfilt -H --decompose=tw in | tee out.tw
-run 0 $autfilt -H --decompose=ws in | tee out.ws
-run 0 $autfilt -H --decompose=tws in | tee out.tws
+run 0 $autfilt -H --decompose-strength=t in | tee out.t
+run 0 $autfilt -H --decompose-strength=w in | tee out.w
+run 0 $autfilt -H --decompose-strength=s in | tee out.s
+run 0 $autfilt -H --decompose-strength=tw in | tee out.tw
+run 0 $autfilt -H --decompose-strength=ws in | tee out.ws
+run 0 $autfilt -H --decompose-strength=tws in | tee out.tws
 echo '/******************************/' > sep
 cat out.t sep out.w sep out.s sep out.tw sep out.ws sep out.tws > out