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dbranch: fix handling of state-based acceptance

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Fixes issue #525.

* spot/twaalgos/dbranch.hh, NEWS: Document.
* spot/twaalgos/dbranch.cc: Detect cases where the acceptance should
be changed from state-based to transition-based.
* tests/python/dbranch.py: Add a test case.
This commit is contained in:
Alexandre Duret-Lutz 2023-02-03 09:35:46 +01:00
parent bdaa31ef21
commit 43b4d80da1
4 changed files with 59 additions and 8 deletions
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19
spot/twaalgos/dbranch.cc
View file

@ -66,6 +66,10 @@ namespace spot
hashmap_t first_dest[1 + is_game];
auto& g = aut->get_graph();
// Merging outgoing transitions may cause the automaton to need
// transition-based acceptance.
bool need_trans = !aut->prop_state_acc().is_true();
// setup a DFS
std::vector<bool> seen(ns);
std::stack<unsigned> todo;
@ -128,9 +132,18 @@ namespace spot
unsigned& mergedlast = g.state_storage(mergedst).succ_tail;
unsigned& candfirst = g.state_storage(canddst).succ;
if (mergedlast)
aut->edge_storage(mergedlast).next_succ = candfirst;
{
aut->edge_storage(mergedlast).next_succ = candfirst;
// Do we need to require transition-based acceptance?
if (!need_trans)
need_trans =
(aut->edge_storage(candfirst).acc
!= aut->edge_storage(mergedfirst).acc);
}
else // mergedst had no successor
mergedfirst = candfirst;
{
mergedfirst = candfirst;
}
mergedlast = candlast;
// 2) updating the source of the merged transitions
for (unsigned e2 = candfirst; e2 != 0;)
@ -149,6 +162,8 @@ namespace spot
changed = true;
}
}
if (need_trans)
aut->prop_state_acc(false);
return changed;
}
}

15
spot/twaalgos/dbranch.hh
View file

@ -1,5 +1,5 @@
// -*- coding: utf-8 -*-
// Copyright (C) 2022 Laboratoire de Recherche et Développement
// Copyright (C) 2022, 2023 Laboratoire de Recherche et Développement
// de l'Epita (LRDE).
//
// This file is part of Spot, a model checking library.
@ -26,10 +26,15 @@ namespace spot
/// \ingroup twa_algorithms
/// \brief Merge states to delay
///
/// If a state (x) has two outgoing transitions (x,l,m,y) and
/// (x,l,m,z) going to states (x) and (y) that have no other
/// incoming edges, then (y) and (z) can be merged (keeping the
/// union of their outgoing destinations).
/// In an automaton with transition-based acceptance, if a state (x)
/// has two outgoing transitions (x,l,m,y) and (x,l,m,z) going to
/// states (x) and (y) that have no other incoming edges, then (y)
/// and (z) can be merged (keeping the union of their outgoing
/// destinations).
///
/// If the input automaton uses state-based acceptance, running this
/// function might make the acceptance transition-based, but only if
/// two states with different acceptance are merged at some point.
///
/// \return true iff the automaton was modified.
SPOT_API bool delay_branching_here(const twa_graph_ptr& aut);