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Fix: Variant cycle detection in FinaliseEngineArray (#14629)

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Jonathan G Rennison
2025-09-17 22:42:42 +01:00
committed by dP
parent afd0313802
commit a39cd7a8ef
1 changed files with 8 additions and 2 deletions
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10
src/newgrf.cpp
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@@ -904,12 +904,18 @@ static void FinaliseEngineArray()
}
/* Check engine variants don't point back on themselves (either directly or via a loop) then set appropriate flags
* on variant engine. This is performed separately as all variant engines need to have been resolved. */
* on variant engine. This is performed separately as all variant engines need to have been resolved.
* Use Floyd's cycle-detection algorithm to handle the case where a cycle is present but does
* not include the starting engine ID. */
for (Engine *e : Engine::Iterate()) {
EngineID parent = e->info.variant_id;
EngineID parent_slow = parent;
bool update_slow = false;
while (parent != EngineID::Invalid()) {
parent = Engine::Get(parent)->info.variant_id;
if (parent != e->index) continue;
if (update_slow) parent_slow = Engine::Get(parent_slow)->info.variant_id;
update_slow = !update_slow;
if (parent != e->index && parent != parent_slow) continue;
/* Engine looped back on itself, so clear the variant. */
e->info.variant_id = EngineID::Invalid();