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Update backtrack_path() to use one less lookup in back_map. #888

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Update backtrack_path() to use one less lookup in back_map. #888

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7 changes: 4 additions & 3 deletions src/stim/search/graphlike/algo.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -27,16 +27,17 @@
using namespace stim;
using namespace stim::impl_search_graphlike;

DetectorErrorModel backtrack_path(const std::map<SearchState, SearchState> &back_map, const SearchState &final_state) {
DetectorErrorModel backtrack_path(const std::map<SearchState, SearchState> &back_map, const SearchState &final_state, const SearchState &previous_state) {
DetectorErrorModel out;
auto cur_state = final_state;
auto prev_state = previous_state;
while (true) {
const auto &prev_state = back_map.at(cur_state);
cur_state.append_transition_as_error_instruction_to(prev_state, out);
if (prev_state.is_undetected()) {
break;
}
cur_state = prev_state;
prev_state = back_map.at(cur_state);
}
std::sort(out.instructions.begin(), out.instructions.end());
return out;
Expand Down Expand Up @@ -82,7 +83,7 @@ DetectorErrorModel stim::shortest_graphlike_undetectable_logical_error(
}
if (next.is_undetected()) {
assert(next.obs_mask.not_zero()); // Otherwise, it would have already been in back_map.
return backtrack_path(back_map, next);
return backtrack_path(back_map, next, curr);
} else {
if (next.det_active == NO_NODE_INDEX) {
// Just resolved one out of two excitations. Move on to the second excitation.
Expand Down