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fix: stop REQ section growth at the minimum section size #566

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fix: stop REQ section growth at the minimum section size #566

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da633fc
fix: stop REQ section growth at the minimum section size
proost Nov 6, 2026
9be4f5f
fix: cast
proost Nov 6, 2026
bd03985
test: revert dead test code
proost Nov 7, 2026
e0abfb2
Merge branch 'master' of github.com:apache/datasketches-cpp into fix-…
proost Nov 7, 2026
6d41569
test: pass k and level to req_compactor::deserialize
proost Nov 7, 2026
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4 changes: 3 additions & 1 deletion req/include/req_compactor_impl.hpp
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Original file line number Diff line number Diff line change
Expand Up @@ -301,7 +301,9 @@ template<typename T, typename C, typename A>
bool req_compactor<T, C, A>::ensure_enough_sections() {
const float ssr = section_size_raw_ / sqrtf(2);
const uint32_t ne = nearest_even(ssr);
if (state_ >= static_cast<uint64_t>(1ULL << (num_sections_ - 1)) && ne >= req_constants::MIN_K) {
if (state_ >= static_cast<uint64_t>(1ULL << (num_sections_ - 1))
&& section_size_ > req_constants::MIN_K
&& ne >= req_constants::MIN_K) {
section_size_raw_ = ssr;
section_size_ = ne;
num_sections_ <<= 1;
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31 changes: 30 additions & 1 deletion req/test/req_sketch_test.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -593,7 +593,6 @@ TEST_CASE("get_rank equivalence") {
// sketch.serialize(os);
//}


template<typename Bytes, typename V>
static void put_value(Bytes& bytes, size_t offset, V value) {
std::memcpy(bytes.data() + offset, &value, sizeof(value));
Expand Down Expand Up @@ -734,4 +733,34 @@ TEST_CASE("req sketch: deserialize rejects inconsistent compactors", "[req_sketc
}
}

using req_compactor_float = req_compactor<float, std::less<float>, std::allocator<float>>;

static req_compactor_float make_compactor_with_state(uint16_t k, uint64_t state) {
std::stringstream s(std::ios::in | std::ios::out | std::ios::binary);
const float section_size_raw = k; // not used by merge
const uint8_t lg_weight = 0;
const uint8_t num_sections = req_constants::INIT_NUM_SECTIONS;
const uint16_t padding = 0;
const uint32_t num_items = 0;
s.write(reinterpret_cast<const char*>(&state), sizeof(state));
s.write(reinterpret_cast<const char*>(&section_size_raw), sizeof(section_size_raw));
s.write(reinterpret_cast<const char*>(&lg_weight), sizeof(lg_weight));
s.write(reinterpret_cast<const char*>(&num_sections), sizeof(num_sections));
s.write(reinterpret_cast<const char*>(&padding), sizeof(padding));
s.write(reinterpret_cast<const char*>(&num_items), sizeof(num_items));
return req_compactor_float::deserialize(s, serde<float>(), std::less<float>(), std::allocator<float>(), true, true,
k, 0);
}

TEST_CASE("req compactor: section growth stops at minimum section size", "[req_compactor]") {
const uint16_t ks[] = {6, 12, 14};
const uint32_t expected_nom_capacities[] = {48, 192, 192};
for (size_t i = 0; i < 3; ++i) {
req_compactor_float c(true, 0, ks[i], std::less<float>(), std::allocator<float>());
for (uint8_t lg_state: {2, 5, 11, 23}) c.merge(make_compactor_with_state(ks[i], 1ULL << lg_state));
INFO("k=" << ks[i]);
CHECK(c.get_nom_capacity() == expected_nom_capacities[i]);
}
}

} /* namespace datasketches */
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