From 5143cde0aa40b751680d447bc3b0c52f1cebc9ee Mon Sep 17 00:00:00 2001
From: vhavlena <vohavlena@gmail.com>
Date: Fri, 29 Sep 2023 16:33:52 +0200
Subject: [PATCH] concat: fix when this == aut

---
 src/nfa/concatenation.cc       | 13 +++++++++----
 tests/nfa/nfa-concatenation.cc | 18 ++++++++++++++++++
 2 files changed, 27 insertions(+), 4 deletions(-)

diff --git a/src/nfa/concatenation.cc b/src/nfa/concatenation.cc
index 31d2ae772..f522994e1 100644
--- a/src/nfa/concatenation.cc
+++ b/src/nfa/concatenation.cc
@@ -32,21 +32,26 @@ Nfa& Nfa::concatenate(const Nfa& aut) {
         return st + n;
     };
 
+    // copy the information about aut to save the case when this is the same object as aut.
+    utils::SparseSet<mata::nfa::State> aut_initial = aut.initial;
+    utils::SparseSet<mata::nfa::State> aut_final = aut.final;
+    size_t aut_n = aut.num_of_states();
+    
     this->delta.allocate(n);
     this->delta.append(aut.delta.renumber_targets(upd_fnc));
 
     // set accepting states
     utils::SparseSet<State> new_fin{};
-    new_fin.reserve(n+aut.num_of_states());
-    for(const State& aut_fin : aut.final) {
+    new_fin.reserve(n+aut_n);
+    for(const State& aut_fin : aut_final) {
         new_fin.insert(upd_fnc(aut_fin));
     }
 
     // connect both parts
-    for(const State& ini : aut.initial) {
+    for(const State& ini : aut_initial) {
         const StatePost& ini_post = this->delta[upd_fnc(ini)];
         // is ini state also final?
-        bool is_final = aut.final[ini];
+        bool is_final = aut_final[ini];
         for(const State& fin : this->final) {
             if(is_final) {
                 new_fin.insert(fin);
diff --git a/tests/nfa/nfa-concatenation.cc b/tests/nfa/nfa-concatenation.cc
index 8bc8f831f..9e1f72ee6 100644
--- a/tests/nfa/nfa-concatenation.cc
+++ b/tests/nfa/nfa-concatenation.cc
@@ -730,6 +730,24 @@ TEST_CASE("mata::nfa::concatenate() inplace") {
         CHECK(!result.is_lang_empty());
     }
 
+    SECTION("the same automata") {
+        Nfa lhs{};
+        
+        lhs.add_state();
+        lhs.initial.insert(0);
+        lhs.final.insert(0);
+        lhs.delta.add(0, 58, 0);
+        lhs.delta.add(0, 65, 0);
+        lhs.delta.add(0, 102, 0);
+        lhs.delta.add(0, 112, 0);
+        lhs.delta.add(0, 115, 0);
+        lhs.delta.add(0, 116, 0);
+
+        size_t lhs_size = lhs.num_of_states();
+        Nfa result = lhs.concatenate(lhs);
+        CHECK(result.num_of_states() == lhs_size * 2);
+    }
+
 }
 
 TEST_CASE("Concat_inplace performance", "[.profiling]") {