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user: replace O(N) loop in GetNext<T> with O(1) id lookup #3336

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user: replace O(N) loop in GetNext<T> with O(1) id lookup #3336

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77ededb
user: replace O(N) loop in GetNext<T> with O(1) id lookup
Pradyuman-aviator Jun 13, 2026
75b5517
Merge branch 'main' of https://github.com/Pradyuman-aviator/mujoco in…
Pradyuman-aviator Jun 15, 2026
5470f7e
user: fix GetNext id validation and add fallback for stale ids
Pradyuman-aviator Jun 15, 2026
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15 changes: 12 additions & 3 deletions src/user/user_model.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -1415,10 +1415,19 @@ static mjsElement* GetNext(const std::vector<T*>& list, const mjsElement* child)
return list[0]->spec.element;
}

// TODO: use id for direct indexing instead of a loop
for (unsigned int i = 0; i < list.size()-1; i++) {
// use id for direct indexing if valid
int id = static_cast<const mjCBase*>(child)->id;
if (id >= 0 && id < (int)list.size() && list[id]->spec.element == child) {
if (id + 1 < (int)list.size()) {
return list[id + 1]->spec.element;
}
return nullptr;
}

// fallback to linear search if id is stale or invalid
for (int i = 0; i < (int)list.size() - 1; i++) {
if (list[i]->spec.element == child) {
return list[i+1]->spec.element;
return list[i + 1]->spec.element;
}
}
return nullptr;
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