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fix: do not create map cells when adding or subtracting zero #441

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Merged
HDembinski merged 1 commit into from
Jul 30, 2026
Merged

fix: do not create map cells when adding or subtracting zero #441

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10 changes: 6 additions & 4 deletions include/boost/histogram/storage_adaptor.hpp
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Original file line number Diff line number Diff line change
Expand Up @@ -171,8 +171,9 @@ struct map_impl : T {
if (it != static_cast<T*>(map)->end()) {
it->second += u;
} else {
auto pair = map->emplace(idx, value_type{});
pair.first->second += u;
value_type tmp{};
tmp += u;
if (!(tmp == value_type{})) map->emplace(idx, tmp);
}
return *this;
}
Expand All @@ -184,8 +185,9 @@ struct map_impl : T {
if (it != static_cast<T*>(map)->end()) {
it->second -= u;
} else {
auto pair = map->emplace(idx, value_type{});
pair.first->second -= u;
value_type tmp{};
tmp -= u;
if (!(tmp == value_type{})) map->emplace(idx, tmp);
}
return *this;
}
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17 changes: 17 additions & 0 deletions test/storage_adaptor_test.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -211,6 +211,23 @@ int main() {
BOOST_TEST(std::isnan(static_cast<double>(a[1])));
}

// adding or subtracting zero must not create cells in map-based storage_adaptor
{
using map_t = std::map<std::size_t, double>;
auto a = storage_adaptor<map_t>();
a.reset(4);
a[0] += 0;
a[1] -= 0;
BOOST_TEST_EQ(static_cast<const map_t&>(a).size(), 0);
BOOST_TEST_EQ(a[0], 0);
BOOST_TEST_EQ(a[1], 0);
a[2] += 1;
a[3] -= 1;
BOOST_TEST_EQ(static_cast<const map_t&>(a).size(), 2);
BOOST_TEST_EQ(a[2], 1);
BOOST_TEST_EQ(a[3], -1);
}

// with accumulators::weighted_sum
{
auto a = storage_adaptor<std::vector<accumulators::weighted_sum<double>>>();
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