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//===----------------------------------------------------------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
// UNSUPPORTED: c++03, c++11, c++14, c++17
#include <algorithm>
#include <cassert>
#include <cstddef>
#include <deque>
#include <iterator>
#include <list>
#include <string>
#include <vector>
#include "benchmark/benchmark.h"
#include "../../GenerateInput.h"
auto compute_median(auto first, auto last) {
std::vector v(first, last);
auto middle = v.begin() + v.size() / 2;
std::nth_element(v.begin(), middle, v.end());
return *middle;
}
int main(int argc, char** argv) {
auto std_partition = [](auto first, auto last, auto pred) { return std::partition(first, last, pred); };
// Benchmark {std,ranges}::partition on a fully unpartitionned sequence, i.e. a lot of elements
// have to be moved around in order to partition the range.
{
auto bm = []<class Container>(std::string name, auto partition) {
benchmark::RegisterBenchmark(
name,
[partition](auto& st) {
std::size_t const size = st.range(0);
using ValueType = typename Container::value_type;
Container c;
std::generate_n(std::back_inserter(c), size, [] { return Generate<ValueType>::random(); });
ValueType median = compute_median(c.begin(), c.end());
auto pred1 = [median](auto const& element) { return element < median; };
auto pred2 = [median](auto const& element) { return element > median; };
bool toggle = false;
for ([[maybe_unused]] auto _ : st) {
benchmark::DoNotOptimize(c);
// By toggling the predicate, we have to move almost all elements in the sequence
// to restore the partition.
if (toggle) {
auto result = partition(c.begin(), c.end(), pred1);
benchmark::DoNotOptimize(result);
} else {
auto result = partition(c.begin(), c.end(), pred2);
benchmark::DoNotOptimize(result);
}
toggle = !toggle;
}
})
->Arg(32)
->Arg(50) // non power-of-two
->Arg(1024)
->Arg(8192);
};
// std::partition
bm.operator()<std::vector<int>>("std::partition(vector<int>) (dense)", std_partition);
bm.operator()<std::deque<int>>("std::partition(deque<int>) (dense)", std_partition);
bm.operator()<std::list<int>>("std::partition(list<int>) (dense)", std_partition);
// ranges::partition
bm.operator()<std::vector<int>>("rng::partition(vector<int>) (dense)", std::ranges::partition);
bm.operator()<std::deque<int>>("rng::partition(deque<int>) (dense)", std::ranges::partition);
bm.operator()<std::list<int>>("rng::partition(list<int>) (dense)", std::ranges::partition);
}
// Benchmark {std,ranges}::partition on a mostly partitioned sequence, i.e. only 10% of the elements
// have to be moved around in order to partition the range.
{
auto bm = []<class Container>(std::string name, auto partition) {
benchmark::RegisterBenchmark(
name,
[partition](auto& st) {
std::size_t const size = st.range(0);
using ValueType = typename Container::value_type;
Container c;
std::generate_n(std::back_inserter(c), size, [] { return Generate<ValueType>::random(); });
ValueType median = compute_median(c.begin(), c.end());
auto pred = [median](auto const& element) { return element < median; };
std::partition(c.begin(), c.end(), pred);
// Between iterations, we swap 5% of the elements to the left of the median with 5% of the elements
// to the right of the median. This ensures that the range is slightly unpartitioned.
auto median_it = std::partition_point(c.begin(), c.end(), pred);
auto low = std::next(c.begin(), std::distance(c.begin(), median_it) - (size / 20));
auto high = std::next(median_it, size / 20);
auto shuffle = [&] { std::swap_ranges(low, median_it, high); };
shuffle();
assert(!std::is_partitioned(c.begin(), c.end(), pred));
for ([[maybe_unused]] auto _ : st) {
benchmark::DoNotOptimize(c);
auto result = partition(c.begin(), c.end(), pred);
benchmark::DoNotOptimize(result);
shuffle();
}
})
->Arg(32)
->Arg(50) // non power-of-two
->Arg(1024)
->Arg(8192);
};
// std::partition
bm.operator()<std::vector<int>>("std::partition(vector<int>) (sparse)", std_partition);
bm.operator()<std::deque<int>>("std::partition(deque<int>) (sparse)", std_partition);
bm.operator()<std::list<int>>("std::partition(list<int>) (sparse)", std_partition);
// ranges::partition
bm.operator()<std::vector<int>>("rng::partition(vector<int>) (sparse)", std::ranges::partition);
bm.operator()<std::deque<int>>("rng::partition(deque<int>) (sparse)", std::ranges::partition);
bm.operator()<std::list<int>>("rng::partition(list<int>) (sparse)", std::ranges::partition);
}
benchmark::Initialize(&argc, argv);
benchmark::RunSpecifiedBenchmarks();
benchmark::Shutdown();
return 0;
}
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