nanobench.h

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//  __   _ _______ __   _  _____  ______  _______ __   _ _______ _     _
//  | \  | |_____| | \  | |     | |_____] |______ | \  | |       |_____|
//  |  \_| |     | |  \_| |_____| |_____] |______ |  \_| |_____  |     |
//
// Microbenchmark framework for C++11/14/17/20
// https://github.com/martinus/nanobench
//
// Licensed under the MIT License <http://opensource.org/licenses/MIT>.
// SPDX-License-Identifier: MIT
// Copyright (c) 2019-2021 Martin Ankerl <martin.ankerl@gmail.com>
//
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in all
// copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
// SOFTWARE.

#ifndef ANKERL_NANOBENCH_H_INCLUDED
#define ANKERL_NANOBENCH_H_INCLUDED

// see https://semver.org/
#define ANKERL_NANOBENCH_VERSION_MAJOR 4 // incompatible API changes
#define ANKERL_NANOBENCH_VERSION_MINOR 3 // backwards-compatible changes
#define ANKERL_NANOBENCH_VERSION_PATCH 4 // backwards-compatible bug fixes

// public facing api - as minimal as possible

#include <chrono>  // high_resolution_clock
#include <cstring> // memcpy
#include <iosfwd>  // for std::ostream* custom output target in Config
#include <string>  // all names
#include <vector>  // holds all results

#define ANKERL_NANOBENCH(x) ANKERL_NANOBENCH_PRIVATE_##x()

#define ANKERL_NANOBENCH_PRIVATE_CXX() __cplusplus
#define ANKERL_NANOBENCH_PRIVATE_CXX98() 199711L
#define ANKERL_NANOBENCH_PRIVATE_CXX11() 201103L
#define ANKERL_NANOBENCH_PRIVATE_CXX14() 201402L
#define ANKERL_NANOBENCH_PRIVATE_CXX17() 201703L

#if ANKERL_NANOBENCH(CXX) >= ANKERL_NANOBENCH(CXX17)
#    define ANKERL_NANOBENCH_PRIVATE_NODISCARD() [[nodiscard]]
#else
#    define ANKERL_NANOBENCH_PRIVATE_NODISCARD()
#endif

#if defined(__clang__)
#    define ANKERL_NANOBENCH_PRIVATE_IGNORE_PADDED_PUSH() \
        _Pragma("clang diagnostic push") _Pragma("clang diagnostic ignored \"-Wpadded\"")
#    define ANKERL_NANOBENCH_PRIVATE_IGNORE_PADDED_POP() _Pragma("clang diagnostic pop")
#else
#    define ANKERL_NANOBENCH_PRIVATE_IGNORE_PADDED_PUSH()
#    define ANKERL_NANOBENCH_PRIVATE_IGNORE_PADDED_POP()
#endif

#if defined(__GNUC__)
#    define ANKERL_NANOBENCH_PRIVATE_IGNORE_EFFCPP_PUSH() _Pragma("GCC diagnostic push") _Pragma("GCC diagnostic ignored \"-Weffc++\"")
#    define ANKERL_NANOBENCH_PRIVATE_IGNORE_EFFCPP_POP() _Pragma("GCC diagnostic pop")
#else
#    define ANKERL_NANOBENCH_PRIVATE_IGNORE_EFFCPP_PUSH()
#    define ANKERL_NANOBENCH_PRIVATE_IGNORE_EFFCPP_POP()
#endif

#if defined(ANKERL_NANOBENCH_LOG_ENABLED)
#    include <iostream>
#    define ANKERL_NANOBENCH_LOG(x)                                                 \
        do {                                                                        \
            std::cout << __FUNCTION__ << "@" << __LINE__ << ": " << x << std::endl; \
        } while (0)
#else
#    define ANKERL_NANOBENCH_LOG(x) \
        do {                        \
        } while (0)
#endif

#if defined(__linux__) && defined(PERF_EVENT_IOC_ID) && defined(PERF_COUNT_HW_REF_CPU_CYCLES) && defined(PERF_FLAG_FD_CLOEXEC) && \
    !defined(ANKERL_NANOBENCH_DISABLE_PERF_COUNTERS)
// only enable perf counters on kernel 3.14 which seems to have all the necessary defines. The three PERF_... defines are not in
// kernel 2.6.32 (all others are).
#    define ANKERL_NANOBENCH_PRIVATE_PERF_COUNTERS() 1
#else
#    define ANKERL_NANOBENCH_PRIVATE_PERF_COUNTERS() 0
#endif

#if defined(__clang__)
#    define ANKERL_NANOBENCH_NO_SANITIZE(...) __attribute__((no_sanitize(__VA_ARGS__)))
#else
#    define ANKERL_NANOBENCH_NO_SANITIZE(...)
#endif

#if defined(_MSC_VER)
#    define ANKERL_NANOBENCH_PRIVATE_NOINLINE() __declspec(noinline)
#else
#    define ANKERL_NANOBENCH_PRIVATE_NOINLINE() __attribute__((noinline))
#endif

// workaround missing "is_trivially_copyable" in g++ < 5.0
// See https://stackoverflow.com/a/31798726/48181
#if defined(__GNUC__) && __GNUC__ < 5
#    define ANKERL_NANOBENCH_IS_TRIVIALLY_COPYABLE(...) __has_trivial_copy(__VA_ARGS__)
#else
#    define ANKERL_NANOBENCH_IS_TRIVIALLY_COPYABLE(...) std::is_trivially_copyable<__VA_ARGS__>::value
#endif

// declarations ///////////////////////////////////////////////////////////////////////////////////

namespace ankerl {
namespace nanobench {

using Clock = std::conditional<std::chrono::high_resolution_clock::is_steady, std::chrono::high_resolution_clock,
                               std::chrono::steady_clock>::type;
class Bench;
struct Config;
class Result;
class Rng;
class BigO;

void render(char const* mustacheTemplate, Bench const& bench, std::ostream& out);
void render(std::string const& mustacheTemplate, Bench const& bench, std::ostream& out);

void render(char const* mustacheTemplate, std::vector<Result> const& results, std::ostream& out);
void render(std::string const& mustacheTemplate, std::vector<Result> const& results, std::ostream& out);

// Contains mustache-like templates
namespace templates {

char const* csv() noexcept;

char const* htmlBoxplot() noexcept;

char const* pyperf() noexcept;

char const* json() noexcept;

} // namespace templates

namespace detail {

template <typename T>
struct PerfCountSet;

class IterationLogic;
class PerformanceCounters;

#if ANKERL_NANOBENCH(PERF_COUNTERS)
class LinuxPerformanceCounters;
#endif

} // namespace detail
} // namespace nanobench
} // namespace ankerl

// definitions ////////////////////////////////////////////////////////////////////////////////////

namespace ankerl {
namespace nanobench {
namespace detail {

template <typename T>
struct PerfCountSet {
    T pageFaults{};
    T cpuCycles{};
    T contextSwitches{};
    T instructions{};
    T branchInstructions{};
    T branchMisses{};
};

} // namespace detail

ANKERL_NANOBENCH(IGNORE_PADDED_PUSH)
struct Config {
    // actual benchmark config
    std::string mBenchmarkTitle = "benchmark";
    std::string mBenchmarkName = "noname";
    std::string mUnit = "op";
    double mBatch = 1.0;
    double mComplexityN = -1.0;
    size_t mNumEpochs = 11;
    size_t mClockResolutionMultiple = static_cast<size_t>(1000);
    std::chrono::nanoseconds mMaxEpochTime = std::chrono::milliseconds(100);
    std::chrono::nanoseconds mMinEpochTime{};
    uint64_t mMinEpochIterations{1};
    uint64_t mEpochIterations{0}; // If not 0, run *exactly* these number of iterations per epoch.
    uint64_t mWarmup = 0;
    std::ostream* mOut = nullptr;
    std::chrono::duration<double> mTimeUnit = std::chrono::nanoseconds{1};
    std::string mTimeUnitName = "ns";
    bool mShowPerformanceCounters = true;
    bool mIsRelative = false;

    Config();
    ~Config();
    Config& operator=(Config const&);
    Config& operator=(Config&&);
    Config(Config const&);
    Config(Config&&) noexcept;
};
ANKERL_NANOBENCH(IGNORE_PADDED_POP)

// Result returned after a benchmark has finished. Can be used as a baseline for relative().
ANKERL_NANOBENCH(IGNORE_PADDED_PUSH)
class Result {
public:
    enum class Measure : size_t {
        elapsed,
        iterations,
        pagefaults,
        cpucycles,
        contextswitches,
        instructions,
        branchinstructions,
        branchmisses,
        _size
    };

    explicit Result(Config const& benchmarkConfig);

    ~Result();
    Result& operator=(Result const&);
    Result& operator=(Result&&);
    Result(Result const&);
    Result(Result&&) noexcept;

    // adds new measurement results
    // all values are scaled by iters (except iters...)
    void add(Clock::duration totalElapsed, uint64_t iters, detail::PerformanceCounters const& pc);

    ANKERL_NANOBENCH(NODISCARD) Config const& config() const noexcept;

    ANKERL_NANOBENCH(NODISCARD) double median(Measure m) const;
    ANKERL_NANOBENCH(NODISCARD) double medianAbsolutePercentError(Measure m) const;
    ANKERL_NANOBENCH(NODISCARD) double average(Measure m) const;
    ANKERL_NANOBENCH(NODISCARD) double sum(Measure m) const noexcept;
    ANKERL_NANOBENCH(NODISCARD) double sumProduct(Measure m1, Measure m2) const noexcept;
    ANKERL_NANOBENCH(NODISCARD) double minimum(Measure m) const noexcept;
    ANKERL_NANOBENCH(NODISCARD) double maximum(Measure m) const noexcept;

    ANKERL_NANOBENCH(NODISCARD) bool has(Measure m) const noexcept;
    ANKERL_NANOBENCH(NODISCARD) double get(size_t idx, Measure m) const;
    ANKERL_NANOBENCH(NODISCARD) bool empty() const noexcept;
    ANKERL_NANOBENCH(NODISCARD) size_t size() const noexcept;

    // Finds string, if not found, returns _size.
    static Measure fromString(std::string const& str);

private:
    Config mConfig{};
    std::vector<std::vector<double>> mNameToMeasurements{};
};
ANKERL_NANOBENCH(IGNORE_PADDED_POP)


class Rng final {
public:
    using result_type = uint64_t;

    static constexpr uint64_t(min)();
    static constexpr uint64_t(max)();

    Rng(Rng const&) = delete;

    Rng& operator=(Rng const&) = delete;

    // moving is ok
    Rng(Rng&&) noexcept = default;
    Rng& operator=(Rng&&) noexcept = default;
    ~Rng() noexcept = default;

    Rng();

    explicit Rng(uint64_t seed) noexcept;
    Rng(uint64_t x, uint64_t y) noexcept;
    Rng(std::vector<uint64_t> const& data);

    ANKERL_NANOBENCH(NODISCARD) Rng copy() const noexcept;

    inline uint64_t operator()() noexcept;

    // This is slightly biased. See

    inline uint32_t bounded(uint32_t range) noexcept;

    // random double in range [0, 1(
    // see http://prng.di.unimi.it/

    inline double uniform01() noexcept;

    template <typename Container>
    void shuffle(Container& container) noexcept;

    std::vector<uint64_t> state() const;

private:
    static constexpr uint64_t rotl(uint64_t x, unsigned k) noexcept;

    uint64_t mX;
    uint64_t mY;
};

ANKERL_NANOBENCH(IGNORE_PADDED_PUSH)
class Bench {
public:
    Bench();

    Bench(Bench&& other);
    Bench& operator=(Bench&& other);
    Bench(Bench const& other);
    Bench& operator=(Bench const& other);
    ~Bench() noexcept;

    template <typename Op>
    ANKERL_NANOBENCH(NOINLINE)
    Bench& run(char const* benchmarkName, Op&& op);

    template <typename Op>
    ANKERL_NANOBENCH(NOINLINE)
    Bench& run(std::string const& benchmarkName, Op&& op);

    template <typename Op>
    ANKERL_NANOBENCH(NOINLINE)
    Bench& run(Op&& op);

    Bench& title(char const* benchmarkTitle);
    Bench& title(std::string const& benchmarkTitle);
    ANKERL_NANOBENCH(NODISCARD) std::string const& title() const noexcept;

    Bench& name(char const* benchmarkName);
    Bench& name(std::string const& benchmarkName);
    ANKERL_NANOBENCH(NODISCARD) std::string const& name() const noexcept;

    template <typename T>
    Bench& batch(T b) noexcept;
    ANKERL_NANOBENCH(NODISCARD) double batch() const noexcept;

    Bench& unit(char const* unit);
    Bench& unit(std::string const& unit);
    ANKERL_NANOBENCH(NODISCARD) std::string const& unit() const noexcept;

    Bench& timeUnit(std::chrono::duration<double> const& tu, std::string const& tuName);
    ANKERL_NANOBENCH(NODISCARD) std::string const& timeUnitName() const noexcept;
    ANKERL_NANOBENCH(NODISCARD) std::chrono::duration<double> const& timeUnit() const noexcept;

    Bench& output(std::ostream* outstream) noexcept;
    ANKERL_NANOBENCH(NODISCARD) std::ostream* output() const noexcept;

    Bench& clockResolutionMultiple(size_t multiple) noexcept;
    ANKERL_NANOBENCH(NODISCARD) size_t clockResolutionMultiple() const noexcept;

    Bench& epochs(size_t numEpochs) noexcept;
    ANKERL_NANOBENCH(NODISCARD) size_t epochs() const noexcept;

    Bench& maxEpochTime(std::chrono::nanoseconds t) noexcept;
    ANKERL_NANOBENCH(NODISCARD) std::chrono::nanoseconds maxEpochTime() const noexcept;

    Bench& minEpochTime(std::chrono::nanoseconds t) noexcept;
    ANKERL_NANOBENCH(NODISCARD) std::chrono::nanoseconds minEpochTime() const noexcept;

    Bench& minEpochIterations(uint64_t numIters) noexcept;
    ANKERL_NANOBENCH(NODISCARD) uint64_t minEpochIterations() const noexcept;

    Bench& epochIterations(uint64_t numIters) noexcept;
    ANKERL_NANOBENCH(NODISCARD) uint64_t epochIterations() const noexcept;

    Bench& warmup(uint64_t numWarmupIters) noexcept;
    ANKERL_NANOBENCH(NODISCARD) uint64_t warmup() const noexcept;

    Bench& relative(bool isRelativeEnabled) noexcept;
    ANKERL_NANOBENCH(NODISCARD) bool relative() const noexcept;

    Bench& performanceCounters(bool showPerformanceCounters) noexcept;
    ANKERL_NANOBENCH(NODISCARD) bool performanceCounters() const noexcept;

    ANKERL_NANOBENCH(NODISCARD) std::vector<Result> const& results() const noexcept;

    template <typename Arg>
    Bench& doNotOptimizeAway(Arg&& arg);

    template <typename T>
    Bench& complexityN(T b) noexcept;
    ANKERL_NANOBENCH(NODISCARD) double complexityN() const noexcept;

    std::vector<BigO> complexityBigO() const;

    template <typename Op>
    BigO complexityBigO(char const* name, Op op) const;

    template <typename Op>
    BigO complexityBigO(std::string const& name, Op op) const;

    Bench& render(char const* templateContent, std::ostream& os);
    Bench& render(std::string const& templateContent, std::ostream& os);

    Bench& config(Config const& benchmarkConfig);
    ANKERL_NANOBENCH(NODISCARD) Config const& config() const noexcept;

private:
    Config mConfig{};
    std::vector<Result> mResults{};
};
ANKERL_NANOBENCH(IGNORE_PADDED_POP)


template <typename Arg>
void doNotOptimizeAway(Arg&& arg);

namespace detail {

#if defined(_MSC_VER)
void doNotOptimizeAwaySink(void const*);

template <typename T>
void doNotOptimizeAway(T const& val);

#else

// These assembly magic is directly from what Google Benchmark is doing. I have previously used what facebook's folly was doing, but
// this seemd to have compilation problems in some cases. Google Benchmark seemed to be the most well tested anyways.
// see https://github.com/google/benchmark/blob/master/include/benchmark/benchmark.h#L307
template <typename T>
void doNotOptimizeAway(T const& val) {
    // NOLINTNEXTLINE(hicpp-no-assembler)
    asm volatile("" : : "r,m"(val) : "memory");
}

template <typename T>
void doNotOptimizeAway(T& val) {
#    if defined(__clang__)
    // NOLINTNEXTLINE(hicpp-no-assembler)
    asm volatile("" : "+r,m"(val) : : "memory");
#    else
    // NOLINTNEXTLINE(hicpp-no-assembler)
    asm volatile("" : "+m,r"(val) : : "memory");
#    endif
}
#endif

// internally used, but visible because run() is templated.
// Not movable/copy-able, so we simply use a pointer instead of unique_ptr. This saves us from
// having to include <memory>, and the template instantiation overhead of unique_ptr which is unfortunately quite significant.
ANKERL_NANOBENCH(IGNORE_EFFCPP_PUSH)
class IterationLogic {
public:
    explicit IterationLogic(Bench const& config) noexcept;
    ~IterationLogic();

    ANKERL_NANOBENCH(NODISCARD) uint64_t numIters() const noexcept;
    void add(std::chrono::nanoseconds elapsed, PerformanceCounters const& pc) noexcept;
    void moveResultTo(std::vector<Result>& results) noexcept;

private:
    struct Impl;
    Impl* mPimpl;
};
ANKERL_NANOBENCH(IGNORE_EFFCPP_POP)

ANKERL_NANOBENCH(IGNORE_PADDED_PUSH)
class PerformanceCounters {
public:
    PerformanceCounters(PerformanceCounters const&) = delete;
    PerformanceCounters& operator=(PerformanceCounters const&) = delete;

    PerformanceCounters();
    ~PerformanceCounters();

    void beginMeasure();
    void endMeasure();
    void updateResults(uint64_t numIters);

    ANKERL_NANOBENCH(NODISCARD) PerfCountSet<uint64_t> const& val() const noexcept;
    ANKERL_NANOBENCH(NODISCARD) PerfCountSet<bool> const& has() const noexcept;

private:
#if ANKERL_NANOBENCH(PERF_COUNTERS)
    LinuxPerformanceCounters* mPc = nullptr;
#endif
    PerfCountSet<uint64_t> mVal{};
    PerfCountSet<bool> mHas{};
};
ANKERL_NANOBENCH(IGNORE_PADDED_POP)

// Gets the singleton
PerformanceCounters& performanceCounters();

} // namespace detail

class BigO {
public:
    using RangeMeasure = std::vector<std::pair<double, double>>;

    template <typename Op>
    static RangeMeasure mapRangeMeasure(RangeMeasure data, Op op) {
        for (auto& rangeMeasure : data) {
            rangeMeasure.first = op(rangeMeasure.first);
        }
        return data;
    }

    static RangeMeasure collectRangeMeasure(std::vector<Result> const& results);

    template <typename Op>
    BigO(char const* bigOName, RangeMeasure const& rangeMeasure, Op rangeToN)
        : BigO(bigOName, mapRangeMeasure(rangeMeasure, rangeToN)) {}

    template <typename Op>
    BigO(std::string const& bigOName, RangeMeasure const& rangeMeasure, Op rangeToN)
        : BigO(bigOName, mapRangeMeasure(rangeMeasure, rangeToN)) {}

    BigO(char const* bigOName, RangeMeasure const& scaledRangeMeasure);
    BigO(std::string const& bigOName, RangeMeasure const& scaledRangeMeasure);
    ANKERL_NANOBENCH(NODISCARD) std::string const& name() const noexcept;
    ANKERL_NANOBENCH(NODISCARD) double constant() const noexcept;
    ANKERL_NANOBENCH(NODISCARD) double normalizedRootMeanSquare() const noexcept;
    ANKERL_NANOBENCH(NODISCARD) bool operator<(BigO const& other) const noexcept;

private:
    std::string mName{};
    double mConstant{};
    double mNormalizedRootMeanSquare{};
};
std::ostream& operator<<(std::ostream& os, BigO const& bigO);
std::ostream& operator<<(std::ostream& os, std::vector<ankerl::nanobench::BigO> const& bigOs);

} // namespace nanobench
} // namespace ankerl

// implementation /////////////////////////////////////////////////////////////////////////////////

namespace ankerl {
namespace nanobench {

constexpr uint64_t(Rng::min)() {
    return 0;
}

constexpr uint64_t(Rng::max)() {
    return (std::numeric_limits<uint64_t>::max)();
}

ANKERL_NANOBENCH_NO_SANITIZE("integer", "undefined")
uint64_t Rng::operator()() noexcept {
    auto x = mX;

    mX = UINT64_C(15241094284759029579) * mY;
    mY = rotl(mY - x, 27);

    return x;
}

ANKERL_NANOBENCH_NO_SANITIZE("integer", "undefined")
uint32_t Rng::bounded(uint32_t range) noexcept {
    uint64_t r32 = static_cast<uint32_t>(operator()());
    auto multiresult = r32 * range;
    return static_cast<uint32_t>(multiresult >> 32U);
}

double Rng::uniform01() noexcept {
    auto i = (UINT64_C(0x3ff) << 52U) | (operator()() >> 12U);
    // can't use union in c++ here for type puning, it's undefined behavior.
    // std::memcpy is optimized anyways.
    double d;
    std::memcpy(&d, &i, sizeof(double));
    return d - 1.0;
}

template <typename Container>
void Rng::shuffle(Container& container) noexcept {
    auto size = static_cast<uint32_t>(container.size());
    for (auto i = size; i > 1U; --i) {
        using std::swap;
        auto p = bounded(i); // number in [0, i)
        swap(container[i - 1], container[p]);
    }
}

ANKERL_NANOBENCH_NO_SANITIZE("integer", "undefined")
constexpr uint64_t Rng::rotl(uint64_t x, unsigned k) noexcept {
    return (x << k) | (x >> (64U - k));
}

template <typename Op>
ANKERL_NANOBENCH_NO_SANITIZE("integer")
Bench& Bench::run(Op&& op) {
    // It is important that this method is kept short so the compiler can do better optimizations/ inlining of op()
    detail::IterationLogic iterationLogic(*this);
    auto& pc = detail::performanceCounters();

    while (auto n = iterationLogic.numIters()) {
        pc.beginMeasure();
        Clock::time_point before = Clock::now();
        while (n-- > 0) {
            op();
        }
        Clock::time_point after = Clock::now();
        pc.endMeasure();
        pc.updateResults(iterationLogic.numIters());
        iterationLogic.add(after - before, pc);
    }
    iterationLogic.moveResultTo(mResults);
    return *this;
}

// Performs all evaluations.
template <typename Op>
Bench& Bench::run(char const* benchmarkName, Op&& op) {
    name(benchmarkName);
    return run(std::forward<Op>(op));
}

template <typename Op>
Bench& Bench::run(std::string const& benchmarkName, Op&& op) {
    name(benchmarkName);
    return run(std::forward<Op>(op));
}

template <typename Op>
BigO Bench::complexityBigO(char const* benchmarkName, Op op) const {
    return BigO(benchmarkName, BigO::collectRangeMeasure(mResults), op);
}

template <typename Op>
BigO Bench::complexityBigO(std::string const& benchmarkName, Op op) const {
    return BigO(benchmarkName, BigO::collectRangeMeasure(mResults), op);
}

// Set the batch size, e.g. number of processed bytes, or some other metric for the size of the processed data in each iteration.
// Any argument is cast to double.
template <typename T>
Bench& Bench::batch(T b) noexcept {
    mConfig.mBatch = static_cast<double>(b);
    return *this;
}

// Sets the computation complexity of the next run. Any argument is cast to double.
template <typename T>
Bench& Bench::complexityN(T n) noexcept {
    mConfig.mComplexityN = static_cast<double>(n);
    return *this;
}

// Convenience: makes sure none of the given arguments are optimized away by the compiler.
template <typename Arg>
Bench& Bench::doNotOptimizeAway(Arg&& arg) {
    detail::doNotOptimizeAway(std::forward<Arg>(arg));
    return *this;
}

// Makes sure none of the given arguments are optimized away by the compiler.
template <typename Arg>
void doNotOptimizeAway(Arg&& arg) {
    detail::doNotOptimizeAway(std::forward<Arg>(arg));
}

namespace detail {

#if defined(_MSC_VER)
template <typename T>
void doNotOptimizeAway(T const& val) {
    doNotOptimizeAwaySink(&val);
}

#endif

} // namespace detail
} // namespace nanobench
} // namespace ankerl

#if defined(ANKERL_NANOBENCH_IMPLEMENT)

// implementation part - only visible in .cpp

#    include <algorithm> // sort, reverse
#    include <atomic>    // compare_exchange_strong in loop overhead
#    include <cstdlib>   // getenv
#    include <cstring>   // strstr, strncmp
#    include <fstream>   // ifstream to parse proc files
#    include <iomanip>   // setw, setprecision
#    include <iostream>  // cout
#    include <numeric>   // accumulate
#    include <random>    // random_device
#    include <sstream>   // to_s in Number
#    include <stdexcept> // throw for rendering templates
#    include <tuple>     // std::tie
#    if defined(__linux__)
#        include <unistd.h> //sysconf
#    endif
#    if ANKERL_NANOBENCH(PERF_COUNTERS)
#        include <map> // map

#        include <linux/perf_event.h>
#        include <sys/ioctl.h>
#        include <sys/syscall.h>
#        include <unistd.h>
#    endif

// declarations ///////////////////////////////////////////////////////////////////////////////////

namespace ankerl {
namespace nanobench {

// helper stuff that is only intended to be used internally
namespace detail {

struct TableInfo;

// formatting utilities
namespace fmt {

class NumSep;
class StreamStateRestorer;
class Number;
class MarkDownColumn;
class MarkDownCode;

} // namespace fmt
} // namespace detail
} // namespace nanobench
} // namespace ankerl

// definitions ////////////////////////////////////////////////////////////////////////////////////

namespace ankerl {
namespace nanobench {

uint64_t splitMix64(uint64_t& state) noexcept;

namespace detail {

// helpers to get double values
template <typename T>
inline double d(T t) noexcept {
    return static_cast<double>(t);
}
inline double d(Clock::duration duration) noexcept {
    return std::chrono::duration_cast<std::chrono::duration<double>>(duration).count();
}

// Calculates clock resolution once, and remembers the result
inline Clock::duration clockResolution() noexcept;

} // namespace detail

namespace templates {

char const* csv() noexcept {
    return R"DELIM("title";"name";"unit";"batch";"elapsed";"error %";"instructions";"branches";"branch misses";"total"
{{#result}}"{{title}}";"{{name}}";"{{unit}}";{{batch}};{{median(elapsed)}};{{medianAbsolutePercentError(elapsed)}};{{median(instructions)}};{{median(branchinstructions)}};{{median(branchmisses)}};{{sumProduct(iterations, elapsed)}}
{{/result}})DELIM";
}

char const* htmlBoxplot() noexcept {
    return R"DELIM(<html>

<head>
    <script src="https://cdn.plot.ly/plotly-latest.min.js"></script>
</head>

<body>
    <div id="myDiv"></div>
    <script>
        var data = [
            {{#result}}{
                name: '{{name}}',
                y: [{{#measurement}}{{elapsed}}{{^-last}}, {{/last}}{{/measurement}}],
            },
            {{/result}}
        ];
        var title = '{{title}}';

        data = data.map(a => Object.assign(a, { boxpoints: 'all', pointpos: 0, type: 'box' }));
        var layout = { title: { text: title }, showlegend: false, yaxis: { title: 'time per unit', rangemode: 'tozero', autorange: true } }; Plotly.newPlot('myDiv', data, layout, {responsive: true});
    </script>
</body>

</html>)DELIM";
}

char const* pyperf() noexcept {
    return R"DELIM({
    "benchmarks": [
        {
            "runs": [
                {
                    "values": [
{{#measurement}}                        {{elapsed}}{{^-last}},
{{/last}}{{/measurement}}
                    ]
                }
            ]
        }
    ],
    "metadata": {
        "loops": {{sum(iterations)}},
        "inner_loops": {{batch}},
        "name": "{{title}}",
        "unit": "second"
    },
    "version": "1.0"
})DELIM";
}

char const* json() noexcept {
    return R"DELIM({
    "results": [
{{#result}}        {
            "title": "{{title}}",
            "name": "{{name}}",
            "unit": "{{unit}}",
            "batch": {{batch}},
            "complexityN": {{complexityN}},
            "epochs": {{epochs}},
            "clockResolution": {{clockResolution}},
            "clockResolutionMultiple": {{clockResolutionMultiple}},
            "maxEpochTime": {{maxEpochTime}},
            "minEpochTime": {{minEpochTime}},
            "minEpochIterations": {{minEpochIterations}},
            "epochIterations": {{epochIterations}},
            "warmup": {{warmup}},
            "relative": {{relative}},
            "median(elapsed)": {{median(elapsed)}},
            "medianAbsolutePercentError(elapsed)": {{medianAbsolutePercentError(elapsed)}},
            "median(instructions)": {{median(instructions)}},
            "medianAbsolutePercentError(instructions)": {{medianAbsolutePercentError(instructions)}},
            "median(cpucycles)": {{median(cpucycles)}},
            "median(contextswitches)": {{median(contextswitches)}},
            "median(pagefaults)": {{median(pagefaults)}},
            "median(branchinstructions)": {{median(branchinstructions)}},
            "median(branchmisses)": {{median(branchmisses)}},
            "totalTime": {{sumProduct(iterations, elapsed)}},
            "measurements": [
{{#measurement}}                {
                    "iterations": {{iterations}},
                    "elapsed": {{elapsed}},
                    "pagefaults": {{pagefaults}},
                    "cpucycles": {{cpucycles}},
                    "contextswitches": {{contextswitches}},
                    "instructions": {{instructions}},
                    "branchinstructions": {{branchinstructions}},
                    "branchmisses": {{branchmisses}}
                }{{^-last}},{{/-last}}
{{/measurement}}            ]
        }{{^-last}},{{/-last}}
{{/result}}    ]
})DELIM";
}

ANKERL_NANOBENCH(IGNORE_PADDED_PUSH)
struct Node {
    enum class Type { tag, content, section, inverted_section };

    char const* begin;
    char const* end;
    std::vector<Node> children;
    Type type;

    template <size_t N>
    // NOLINTNEXTLINE(hicpp-avoid-c-arrays,modernize-avoid-c-arrays,cppcoreguidelines-avoid-c-arrays)
    bool operator==(char const (&str)[N]) const noexcept {
        return static_cast<size_t>(std::distance(begin, end) + 1) == N && 0 == strncmp(str, begin, N - 1);
    }
};
ANKERL_NANOBENCH(IGNORE_PADDED_POP)

static std::vector<Node> parseMustacheTemplate(char const** tpl) {
    std::vector<Node> nodes;

    while (true) {
        auto begin = std::strstr(*tpl, "{{");
        auto end = begin;
        if (begin != nullptr) {
            begin += 2;
            end = std::strstr(begin, "}}");
        }

        if (begin == nullptr || end == nullptr) {
            // nothing found, finish node
            nodes.emplace_back(Node{*tpl, *tpl + std::strlen(*tpl), std::vector<Node>{}, Node::Type::content});
            return nodes;
        }

        nodes.emplace_back(Node{*tpl, begin - 2, std::vector<Node>{}, Node::Type::content});

        // we found a tag
        *tpl = end + 2;
        switch (*begin) {
        case '/':
            // finished! bail out
            return nodes;

        case '#':
            nodes.emplace_back(Node{begin + 1, end, parseMustacheTemplate(tpl), Node::Type::section});
            break;

        case '^':
            nodes.emplace_back(Node{begin + 1, end, parseMustacheTemplate(tpl), Node::Type::inverted_section});
            break;

        default:
            nodes.emplace_back(Node{begin, end, std::vector<Node>{}, Node::Type::tag});
            break;
        }
    }
}

static bool generateFirstLast(Node const& n, size_t idx, size_t size, std::ostream& out) {
    ANKERL_NANOBENCH_LOG("n.type=" << static_cast<int>(n.type));
    bool matchFirst = n == "-first";
    bool matchLast = n == "-last";
    if (!matchFirst && !matchLast) {
        return false;
    }

    bool doWrite = false;
    if (n.type == Node::Type::section) {
        doWrite = (matchFirst && idx == 0) || (matchLast && idx == size - 1);
    } else if (n.type == Node::Type::inverted_section) {
        doWrite = (matchFirst && idx != 0) || (matchLast && idx != size - 1);
    }

    if (doWrite) {
        for (auto const& child : n.children) {
            if (child.type == Node::Type::content) {
                out.write(child.begin, std::distance(child.begin, child.end));
            }
        }
    }
    return true;
}

static bool matchCmdArgs(std::string const& str, std::vector<std::string>& matchResult) {
    matchResult.clear();
    auto idxOpen = str.find('(');
    auto idxClose = str.find(')', idxOpen);
    if (idxClose == std::string::npos) {
        return false;
    }

    matchResult.emplace_back(str.substr(0, idxOpen));

    // split by comma
    matchResult.emplace_back(std::string{});
    for (size_t i = idxOpen + 1; i != idxClose; ++i) {
        if (str[i] == ' ' || str[i] == '\t') {
            // skip whitespace
            continue;
        }
        if (str[i] == ',') {
            // got a comma => new string
            matchResult.emplace_back(std::string{});
            continue;
        }
        // no whitespace no comma, append
        matchResult.back() += str[i];
    }
    return true;
}

static bool generateConfigTag(Node const& n, Config const& config, std::ostream& out) {
    using detail::d;

    if (n == "title") {
        out << config.mBenchmarkTitle;
        return true;
    } else if (n == "name") {
        out << config.mBenchmarkName;
        return true;
    } else if (n == "unit") {
        out << config.mUnit;
        return true;
    } else if (n == "batch") {
        out << config.mBatch;
        return true;
    } else if (n == "complexityN") {
        out << config.mComplexityN;
        return true;
    } else if (n == "epochs") {
        out << config.mNumEpochs;
        return true;
    } else if (n == "clockResolution") {
        out << d(detail::clockResolution());
        return true;
    } else if (n == "clockResolutionMultiple") {
        out << config.mClockResolutionMultiple;
        return true;
    } else if (n == "maxEpochTime") {
        out << d(config.mMaxEpochTime);
        return true;
    } else if (n == "minEpochTime") {
        out << d(config.mMinEpochTime);
        return true;
    } else if (n == "minEpochIterations") {
        out << config.mMinEpochIterations;
        return true;
    } else if (n == "epochIterations") {
        out << config.mEpochIterations;
        return true;
    } else if (n == "warmup") {
        out << config.mWarmup;
        return true;
    } else if (n == "relative") {
        out << config.mIsRelative;
        return true;
    }
    return false;
}

static std::ostream& generateResultTag(Node const& n, Result const& r, std::ostream& out) {
    if (generateConfigTag(n, r.config(), out)) {
        return out;
    }
    // match e.g. "median(elapsed)"
    // g++ 4.8 doesn't implement std::regex :(
    // static std::regex const regOpArg1("^([a-zA-Z]+)\\(([a-zA-Z]*)\\)$");
    // std::cmatch matchResult;
    // if (std::regex_match(n.begin, n.end, matchResult, regOpArg1)) {
    std::vector<std::string> matchResult;
    if (matchCmdArgs(std::string(n.begin, n.end), matchResult)) {
        if (matchResult.size() == 2) {
            auto m = Result::fromString(matchResult[1]);
            if (m == Result::Measure::_size) {
                return out << 0.0;
            }

            if (matchResult[0] == "median") {
                return out << r.median(m);
            }
            if (matchResult[0] == "average") {
                return out << r.average(m);
            }
            if (matchResult[0] == "medianAbsolutePercentError") {
                return out << r.medianAbsolutePercentError(m);
            }
            if (matchResult[0] == "sum") {
                return out << r.sum(m);
            }
            if (matchResult[0] == "minimum") {
                return out << r.minimum(m);
            }
            if (matchResult[0] == "maximum") {
                return out << r.maximum(m);
            }
        } else if (matchResult.size() == 3) {
            auto m1 = Result::fromString(matchResult[1]);
            auto m2 = Result::fromString(matchResult[2]);
            if (m1 == Result::Measure::_size || m2 == Result::Measure::_size) {
                return out << 0.0;
            }

            if (matchResult[0] == "sumProduct") {
                return out << r.sumProduct(m1, m2);
            }
        }
    }

    // match e.g. "sumProduct(elapsed, iterations)"
    // static std::regex const regOpArg2("^([a-zA-Z]+)\\(([a-zA-Z]*)\\s*,\\s+([a-zA-Z]*)\\)$");

    // nothing matches :(
    throw std::runtime_error("command '" + std::string(n.begin, n.end) + "' not understood");
}

static void generateResultMeasurement(std::vector<Node> const& nodes, size_t idx, Result const& r, std::ostream& out) {
    for (auto const& n : nodes) {
        if (!generateFirstLast(n, idx, r.size(), out)) {
            ANKERL_NANOBENCH_LOG("n.type=" << static_cast<int>(n.type));
            switch (n.type) {
            case Node::Type::content:
                out.write(n.begin, std::distance(n.begin, n.end));
                break;

            case Node::Type::inverted_section:
                throw std::runtime_error("got a inverted section inside measurement");

            case Node::Type::section:
                throw std::runtime_error("got a section inside measurement");

            case Node::Type::tag: {
                auto m = Result::fromString(std::string(n.begin, n.end));
                if (m == Result::Measure::_size || !r.has(m)) {
                    out << 0.0;
                } else {
                    out << r.get(idx, m);
                }
                break;
            }
            }
        }
    }
}

static void generateResult(std::vector<Node> const& nodes, size_t idx, std::vector<Result> const& results, std::ostream& out) {
    auto const& r = results[idx];
    for (auto const& n : nodes) {
        if (!generateFirstLast(n, idx, results.size(), out)) {
            ANKERL_NANOBENCH_LOG("n.type=" << static_cast<int>(n.type));
            switch (n.type) {
            case Node::Type::content:
                out.write(n.begin, std::distance(n.begin, n.end));
                break;

            case Node::Type::inverted_section:
                throw std::runtime_error("got a inverted section inside result");

            case Node::Type::section:
                if (n == "measurement") {
                    for (size_t i = 0; i < r.size(); ++i) {
                        generateResultMeasurement(n.children, i, r, out);
                    }
                } else {
                    throw std::runtime_error("got a section inside result");
                }
                break;

            case Node::Type::tag:
                generateResultTag(n, r, out);
                break;
            }
        }
    }
}

} // namespace templates

// helper stuff that only intended to be used internally
namespace detail {

char const* getEnv(char const* name);
bool isEndlessRunning(std::string const& name);
bool isWarningsEnabled();

template <typename T>
T parseFile(std::string const& filename);

void gatherStabilityInformation(std::vector<std::string>& warnings, std::vector<std::string>& recommendations);
void printStabilityInformationOnce(std::ostream* os);

// remembers the last table settings used. When it changes, a new table header is automatically written for the new entry.
uint64_t& singletonHeaderHash() noexcept;

// determines resolution of the given clock. This is done by measuring multiple times and returning the minimum time difference.
Clock::duration calcClockResolution(size_t numEvaluations) noexcept;

// formatting utilities
namespace fmt {

// adds thousands separator to numbers
ANKERL_NANOBENCH(IGNORE_PADDED_PUSH)
class NumSep : public std::numpunct<char> {
public:
    explicit NumSep(char sep);
    char do_thousands_sep() const override;
    std::string do_grouping() const override;

private:
    char mSep;
};
ANKERL_NANOBENCH(IGNORE_PADDED_POP)

// RAII to save & restore a stream's state
ANKERL_NANOBENCH(IGNORE_PADDED_PUSH)
class StreamStateRestorer {
public:
    explicit StreamStateRestorer(std::ostream& s);
    ~StreamStateRestorer();

    // sets back all stream info that we remembered at construction
    void restore();

    // don't allow copying / moving
    StreamStateRestorer(StreamStateRestorer const&) = delete;
    StreamStateRestorer& operator=(StreamStateRestorer const&) = delete;
    StreamStateRestorer(StreamStateRestorer&&) = delete;
    StreamStateRestorer& operator=(StreamStateRestorer&&) = delete;

private:
    std::ostream& mStream;
    std::locale mLocale;
    std::streamsize const mPrecision;
    std::streamsize const mWidth;
    std::ostream::char_type const mFill;
    std::ostream::fmtflags const mFmtFlags;
};
ANKERL_NANOBENCH(IGNORE_PADDED_POP)

// Number formatter
class Number {
public:
    Number(int width, int precision, double value);
    Number(int width, int precision, int64_t value);
    std::string to_s() const;

private:
    friend std::ostream& operator<<(std::ostream& os, Number const& n);
    std::ostream& write(std::ostream& os) const;

    int mWidth;
    int mPrecision;
    double mValue;
};

// helper replacement for std::to_string of signed/unsigned numbers so we are locale independent
std::string to_s(uint64_t s);

std::ostream& operator<<(std::ostream& os, Number const& n);

class MarkDownColumn {
public:
    MarkDownColumn(int w, int prec, std::string const& tit, std::string const& suff, double val);
    std::string title() const;
    std::string separator() const;
    std::string invalid() const;
    std::string value() const;

private:
    int mWidth;
    int mPrecision;
    std::string mTitle;
    std::string mSuffix;
    double mValue;
};

// Formats any text as markdown code, escaping backticks.
class MarkDownCode {
public:
    explicit MarkDownCode(std::string const& what);

private:
    friend std::ostream& operator<<(std::ostream& os, MarkDownCode const& mdCode);
    std::ostream& write(std::ostream& os) const;

    std::string mWhat{};
};

std::ostream& operator<<(std::ostream& os, MarkDownCode const& mdCode);

} // namespace fmt
} // namespace detail
} // namespace nanobench
} // namespace ankerl

// implementation /////////////////////////////////////////////////////////////////////////////////

namespace ankerl {
namespace nanobench {

void render(char const* mustacheTemplate, std::vector<Result> const& results, std::ostream& out) {
    detail::fmt::StreamStateRestorer restorer(out);

    out.precision(std::numeric_limits<double>::digits10);
    auto nodes = templates::parseMustacheTemplate(&mustacheTemplate);

    for (auto const& n : nodes) {
        ANKERL_NANOBENCH_LOG("n.type=" << static_cast<int>(n.type));
        switch (n.type) {
        case templates::Node::Type::content:
            out.write(n.begin, std::distance(n.begin, n.end));
            break;

        case templates::Node::Type::inverted_section:
            throw std::runtime_error("unknown list '" + std::string(n.begin, n.end) + "'");

        case templates::Node::Type::section:
            if (n == "result") {
                const size_t nbResults = results.size();
                for (size_t i = 0; i < nbResults; ++i) {
                    generateResult(n.children, i, results, out);
                }
            } else if (n == "measurement") {
                if (results.size() != 1) {
                    throw std::runtime_error(
                        "render: can only use section 'measurement' here if there is a single result, but there are " +
                        detail::fmt::to_s(results.size()));
                }
                // when we only have a single result, we can immediately go into its measurement.
                auto const& r = results.front();
                for (size_t i = 0; i < r.size(); ++i) {
                    generateResultMeasurement(n.children, i, r, out);
                }
            } else {
                throw std::runtime_error("render: unknown section '" + std::string(n.begin, n.end) + "'");
            }
            break;

        case templates::Node::Type::tag:
            if (results.size() == 1) {
                // result & config are both supported there
                generateResultTag(n, results.front(), out);
            } else {
                // This just uses the last result's config.
                if (!generateConfigTag(n, results.back().config(), out)) {
                    throw std::runtime_error("unknown tag '" + std::string(n.begin, n.end) + "'");
                }
            }
            break;
        }
    }
}

void render(std::string const& mustacheTemplate, std::vector<Result> const& results, std::ostream& out) {
    render(mustacheTemplate.c_str(), results, out);
}

void render(char const* mustacheTemplate, const Bench& bench, std::ostream& out) {
    render(mustacheTemplate, bench.results(), out);
}

void render(std::string const& mustacheTemplate, const Bench& bench, std::ostream& out) {
    render(mustacheTemplate.c_str(), bench.results(), out);
}

namespace detail {

PerformanceCounters& performanceCounters() {
#    if defined(__clang__)
#        pragma clang diagnostic push
#        pragma clang diagnostic ignored "-Wexit-time-destructors"
#    endif
    static PerformanceCounters pc;
#    if defined(__clang__)
#        pragma clang diagnostic pop
#    endif
    return pc;
}

// Windows version of doNotOptimizeAway
// see https://github.com/google/benchmark/blob/master/include/benchmark/benchmark.h#L307
// see https://github.com/facebook/folly/blob/master/folly/Benchmark.h#L280
// see https://docs.microsoft.com/en-us/cpp/preprocessor/optimize
#    if defined(_MSC_VER)
#        pragma optimize("", off)
void doNotOptimizeAwaySink(void const*) {}
#        pragma optimize("", on)
#    endif

template <typename T>
T parseFile(std::string const& filename) {
    std::ifstream fin(filename);
    T num{};
    fin >> num;
    return num;
}

char const* getEnv(char const* name) {
#    if defined(_MSC_VER)
#        pragma warning(push)
#        pragma warning(disable : 4996) // getenv': This function or variable may be unsafe.
#    endif
    return std::getenv(name);
#    if defined(_MSC_VER)
#        pragma warning(pop)
#    endif
}

bool isEndlessRunning(std::string const& name) {
    auto endless = getEnv("NANOBENCH_ENDLESS");
    return nullptr != endless && endless == name;
}

// True when environment variable NANOBENCH_SUPPRESS_WARNINGS is either not set at all, or set to "0"
bool isWarningsEnabled() {
    auto suppression = getEnv("NANOBENCH_SUPPRESS_WARNINGS");
    return nullptr == suppression || suppression == std::string("0");
}

void gatherStabilityInformation(std::vector<std::string>& warnings, std::vector<std::string>& recommendations) {
    warnings.clear();
    recommendations.clear();

    bool recommendCheckFlags = false;

#    if defined(DEBUG)
    warnings.emplace_back("DEBUG defined");
    recommendCheckFlags = true;
#    endif

    bool recommendPyPerf = false;
#    if defined(__linux__)
    auto nprocs = sysconf(_SC_NPROCESSORS_CONF);
    if (nprocs <= 0) {
        warnings.emplace_back("couldn't figure out number of processors - no governor, turbo check possible");
    } else {

        // check frequency scaling
        for (long id = 0; id < nprocs; ++id) {
            auto idStr = detail::fmt::to_s(static_cast<uint64_t>(id));
            auto sysCpu = "/sys/devices/system/cpu/cpu" + idStr;
            auto minFreq = parseFile<int64_t>(sysCpu + "/cpufreq/scaling_min_freq");
            auto maxFreq = parseFile<int64_t>(sysCpu + "/cpufreq/scaling_max_freq");
            if (minFreq != maxFreq) {
                auto minMHz = static_cast<double>(minFreq) / 1000.0;
                auto maxMHz = static_cast<double>(maxFreq) / 1000.0;
                warnings.emplace_back("CPU frequency scaling enabled: CPU " + idStr + " between " +
                                      detail::fmt::Number(1, 1, minMHz).to_s() + " and " + detail::fmt::Number(1, 1, maxMHz).to_s() +
                                      " MHz");
                recommendPyPerf = true;
                break;
            }
        }

        auto currentGovernor = parseFile<std::string>("/sys/devices/system/cpu/cpu0/cpufreq/scaling_governor");
        if ("performance" != currentGovernor) {
            warnings.emplace_back("CPU governor is '" + currentGovernor + "' but should be 'performance'");
            recommendPyPerf = true;
        }

        if (0 == parseFile<int>("/sys/devices/system/cpu/intel_pstate/no_turbo")) {
            warnings.emplace_back("Turbo is enabled, CPU frequency will fluctuate");
            recommendPyPerf = true;
        }
    }
#    endif

    if (recommendCheckFlags) {
        recommendations.emplace_back("Make sure you compile for Release");
    }
    if (recommendPyPerf) {
        recommendations.emplace_back("Use 'pyperf system tune' before benchmarking. See https://github.com/psf/pyperf");
    }
}

void printStabilityInformationOnce(std::ostream* outStream) {
    static bool shouldPrint = true;
    if (shouldPrint && outStream && isWarningsEnabled()) {
        auto& os = *outStream;
        shouldPrint = false;
        std::vector<std::string> warnings;
        std::vector<std::string> recommendations;
        gatherStabilityInformation(warnings, recommendations);
        if (warnings.empty()) {
            return;
        }

        os << "Warning, results might be unstable:" << std::endl;
        for (auto const& w : warnings) {
            os << "* " << w << std::endl;
        }

        os << std::endl << "Recommendations" << std::endl;
        for (auto const& r : recommendations) {
            os << "* " << r << std::endl;
        }
    }
}

// remembers the last table settings used. When it changes, a new table header is automatically written for the new entry.
uint64_t& singletonHeaderHash() noexcept {
    static uint64_t sHeaderHash{};
    return sHeaderHash;
}

ANKERL_NANOBENCH_NO_SANITIZE("integer", "undefined")
inline uint64_t hash_combine(uint64_t seed, uint64_t val) {
    return seed ^ (val + UINT64_C(0x9e3779b9) + (seed << 6U) + (seed >> 2U));
}

// determines resolution of the given clock. This is done by measuring multiple times and returning the minimum time difference.
Clock::duration calcClockResolution(size_t numEvaluations) noexcept {
    auto bestDuration = Clock::duration::max();
    Clock::time_point tBegin;
    Clock::time_point tEnd;
    for (size_t i = 0; i < numEvaluations; ++i) {
        tBegin = Clock::now();
        do {
            tEnd = Clock::now();
        } while (tBegin == tEnd);
        bestDuration = (std::min)(bestDuration, tEnd - tBegin);
    }
    return bestDuration;
}

// Calculates clock resolution once, and remembers the result
Clock::duration clockResolution() noexcept {
    static Clock::duration sResolution = calcClockResolution(20);
    return sResolution;
}

ANKERL_NANOBENCH(IGNORE_PADDED_PUSH)
struct IterationLogic::Impl {
    enum class State { warmup, upscaling_runtime, measuring, endless };

    explicit Impl(Bench const& bench)
        : mBench(bench)
        , mResult(bench.config()) {
        printStabilityInformationOnce(mBench.output());

        // determine target runtime per epoch
        mTargetRuntimePerEpoch = detail::clockResolution() * mBench.clockResolutionMultiple();
        if (mTargetRuntimePerEpoch > mBench.maxEpochTime()) {
            mTargetRuntimePerEpoch = mBench.maxEpochTime();
        }
        if (mTargetRuntimePerEpoch < mBench.minEpochTime()) {
            mTargetRuntimePerEpoch = mBench.minEpochTime();
        }

        if (isEndlessRunning(mBench.name())) {
            std::cerr << "NANOBENCH_ENDLESS set: running '" << mBench.name() << "' endlessly" << std::endl;
            mNumIters = (std::numeric_limits<uint64_t>::max)();
            mState = State::endless;
        } else if (0 != mBench.warmup()) {
            mNumIters = mBench.warmup();
            mState = State::warmup;
        } else if (0 != mBench.epochIterations()) {
            // exact number of iterations
            mNumIters = mBench.epochIterations();
            mState = State::measuring;
        } else {
            mNumIters = mBench.minEpochIterations();
            mState = State::upscaling_runtime;
        }
    }

    // directly calculates new iters based on elapsed&iters, and adds a 10% noise. Makes sure we don't underflow.
    ANKERL_NANOBENCH(NODISCARD) uint64_t calcBestNumIters(std::chrono::nanoseconds elapsed, uint64_t iters) noexcept {
        auto doubleElapsed = d(elapsed);
        auto doubleTargetRuntimePerEpoch = d(mTargetRuntimePerEpoch);
        auto doubleNewIters = doubleTargetRuntimePerEpoch / doubleElapsed * d(iters);

        auto doubleMinEpochIters = d(mBench.minEpochIterations());
        if (doubleNewIters < doubleMinEpochIters) {
            doubleNewIters = doubleMinEpochIters;
        }
        doubleNewIters *= 1.0 + 0.2 * mRng.uniform01();

        // +0.5 for correct rounding when casting
        // NOLINTNEXTLINE(bugprone-incorrect-roundings)
        return static_cast<uint64_t>(doubleNewIters + 0.5);
    }

    ANKERL_NANOBENCH_NO_SANITIZE("integer", "undefined") void upscale(std::chrono::nanoseconds elapsed) {
        if (elapsed * 10 < mTargetRuntimePerEpoch) {
            // we are far below the target runtime. Multiply iterations by 10 (with overflow check)
            if (mNumIters * 10 < mNumIters) {
                // overflow :-(
                showResult("iterations overflow. Maybe your code got optimized away?");
                mNumIters = 0;
                return;
            }
            mNumIters *= 10;
        } else {
            mNumIters = calcBestNumIters(elapsed, mNumIters);
        }
    }

    void add(std::chrono::nanoseconds elapsed, PerformanceCounters const& pc) noexcept {
#    if defined(ANKERL_NANOBENCH_LOG_ENABLED)
        auto oldIters = mNumIters;
#    endif

        switch (mState) {
        case State::warmup:
            if (isCloseEnoughForMeasurements(elapsed)) {
                // if elapsed is close enough, we can skip upscaling and go right to measurements
                // still, we don't add the result to the measurements.
                mState = State::measuring;
                mNumIters = calcBestNumIters(elapsed, mNumIters);
            } else {
                // not close enough: switch to upscaling
                mState = State::upscaling_runtime;
                upscale(elapsed);
            }
            break;

        case State::upscaling_runtime:
            if (isCloseEnoughForMeasurements(elapsed)) {
                // if we are close enough, add measurement and switch to always measuring
                mState = State::measuring;
                mTotalElapsed += elapsed;
                mTotalNumIters += mNumIters;
                mResult.add(elapsed, mNumIters, pc);
                mNumIters = calcBestNumIters(mTotalElapsed, mTotalNumIters);
            } else {
                upscale(elapsed);
            }
            break;

        case State::measuring:
            // just add measurements - no questions asked. Even when runtime is low. But we can't ignore
            // that fluctuation, or else we would bias the result
            mTotalElapsed += elapsed;
            mTotalNumIters += mNumIters;
            mResult.add(elapsed, mNumIters, pc);
            if (0 != mBench.epochIterations()) {
                mNumIters = mBench.epochIterations();
            } else {
                mNumIters = calcBestNumIters(mTotalElapsed, mTotalNumIters);
            }
            break;

        case State::endless:
            mNumIters = (std::numeric_limits<uint64_t>::max)();
            break;
        }

        if (static_cast<uint64_t>(mResult.size()) == mBench.epochs()) {
            // we got all the results that we need, finish it
            showResult("");
            mNumIters = 0;
        }

        ANKERL_NANOBENCH_LOG(mBench.name() << ": " << detail::fmt::Number(20, 3, static_cast<double>(elapsed.count())) << " elapsed, "
                                           << detail::fmt::Number(20, 3, static_cast<double>(mTargetRuntimePerEpoch.count()))
                                           << " target. oldIters=" << oldIters << ", mNumIters=" << mNumIters
                                           << ", mState=" << static_cast<int>(mState));
    }

    void showResult(std::string const& errorMessage) const {
        ANKERL_NANOBENCH_LOG(errorMessage);

        if (mBench.output() != nullptr) {
            // prepare column data ///////
            std::vector<fmt::MarkDownColumn> columns;

            auto rMedian = mResult.median(Result::Measure::elapsed);

            if (mBench.relative()) {
                double d = 100.0;
                if (!mBench.results().empty()) {
                    d = rMedian <= 0.0 ? 0.0 : mBench.results().front().median(Result::Measure::elapsed) / rMedian * 100.0;
                }
                columns.emplace_back(11, 1, "relative", "%", d);
            }

            if (mBench.complexityN() > 0) {
                columns.emplace_back(14, 0, "complexityN", "", mBench.complexityN());
            }

            columns.emplace_back(22, 2, mBench.timeUnitName() + "/" + mBench.unit(), "",
                                 rMedian / (mBench.timeUnit().count() * mBench.batch()));
            columns.emplace_back(22, 2, mBench.unit() + "/s", "", rMedian <= 0.0 ? 0.0 : mBench.batch() / rMedian);

            double rErrorMedian = mResult.medianAbsolutePercentError(Result::Measure::elapsed);
            columns.emplace_back(10, 1, "err%", "%", rErrorMedian * 100.0);

            double rInsMedian = -1.0;
            if (mResult.has(Result::Measure::instructions)) {
                rInsMedian = mResult.median(Result::Measure::instructions);
                columns.emplace_back(18, 2, "ins/" + mBench.unit(), "", rInsMedian / mBench.batch());
            }

            double rCycMedian = -1.0;
            if (mResult.has(Result::Measure::cpucycles)) {
                rCycMedian = mResult.median(Result::Measure::cpucycles);
                columns.emplace_back(18, 2, "cyc/" + mBench.unit(), "", rCycMedian / mBench.batch());
            }
            if (rInsMedian > 0.0 && rCycMedian > 0.0) {
                columns.emplace_back(9, 3, "IPC", "", rCycMedian <= 0.0 ? 0.0 : rInsMedian / rCycMedian);
            }
            if (mResult.has(Result::Measure::branchinstructions)) {
                double rBraMedian = mResult.median(Result::Measure::branchinstructions);
                columns.emplace_back(17, 2, "bra/" + mBench.unit(), "", rBraMedian / mBench.batch());
                if (mResult.has(Result::Measure::branchmisses)) {
                    double p = 0.0;
                    if (rBraMedian >= 1e-9) {
                        p = 100.0 * mResult.median(Result::Measure::branchmisses) / rBraMedian;
                    }
                    columns.emplace_back(10, 1, "miss%", "%", p);
                }
            }

            columns.emplace_back(12, 2, "total", "", mResult.sumProduct(Result::Measure::iterations, Result::Measure::elapsed));

            // write everything
            auto& os = *mBench.output();

            // combine all elements that are relevant for printing the header
            uint64_t hash = 0;
            hash = hash_combine(std::hash<std::string>{}(mBench.unit()), hash);
            hash = hash_combine(std::hash<std::string>{}(mBench.title()), hash);
            hash = hash_combine(std::hash<std::string>{}(mBench.timeUnitName()), hash);
            hash = hash_combine(std::hash<double>{}(mBench.timeUnit().count()), hash);
            hash = hash_combine(std::hash<bool>{}(mBench.relative()), hash);
            hash = hash_combine(std::hash<bool>{}(mBench.performanceCounters()), hash);

            if (hash != singletonHeaderHash()) {
                singletonHeaderHash() = hash;

                // no result yet, print header
                os << std::endl;
                for (auto const& col : columns) {
                    os << col.title();
                }
                os << "| " << mBench.title() << std::endl;

                for (auto const& col : columns) {
                    os << col.separator();
                }
                os << "|:" << std::string(mBench.title().size() + 1U, '-') << std::endl;
            }

            if (!errorMessage.empty()) {
                for (auto const& col : columns) {
                    os << col.invalid();
                }
                os << "| :boom: " << fmt::MarkDownCode(mBench.name()) << " (" << errorMessage << ')' << std::endl;
            } else {
                for (auto const& col : columns) {
                    os << col.value();
                }
                os << "| ";
                auto showUnstable = isWarningsEnabled() && rErrorMedian >= 0.05;
                if (showUnstable) {
                    os << ":wavy_dash: ";
                }
                os << fmt::MarkDownCode(mBench.name());
                if (showUnstable) {
                    auto avgIters = static_cast<double>(mTotalNumIters) / static_cast<double>(mBench.epochs());
                    // NOLINTNEXTLINE(bugprone-incorrect-roundings)
                    auto suggestedIters = static_cast<uint64_t>(avgIters * 10 + 0.5);

                    os << " (Unstable with ~" << detail::fmt::Number(1, 1, avgIters)
                       << " iters. Increase `minEpochIterations` to e.g. " << suggestedIters << ")";
                }
                os << std::endl;
            }
        }
    }

    ANKERL_NANOBENCH(NODISCARD) bool isCloseEnoughForMeasurements(std::chrono::nanoseconds elapsed) const noexcept {
        return elapsed * 3 >= mTargetRuntimePerEpoch * 2;
    }

    uint64_t mNumIters = 1;
    Bench const& mBench;
    std::chrono::nanoseconds mTargetRuntimePerEpoch{};
    Result mResult;
    Rng mRng{123};
    std::chrono::nanoseconds mTotalElapsed{};
    uint64_t mTotalNumIters = 0;

    State mState = State::upscaling_runtime;
};
ANKERL_NANOBENCH(IGNORE_PADDED_POP)

IterationLogic::IterationLogic(Bench const& bench) noexcept
    : mPimpl(new Impl(bench)) {}

IterationLogic::~IterationLogic() {
    if (mPimpl) {
        delete mPimpl;
    }
}

uint64_t IterationLogic::numIters() const noexcept {
    ANKERL_NANOBENCH_LOG(mPimpl->mBench.name() << ": mNumIters=" << mPimpl->mNumIters);
    return mPimpl->mNumIters;
}

void IterationLogic::add(std::chrono::nanoseconds elapsed, PerformanceCounters const& pc) noexcept {
    mPimpl->add(elapsed, pc);
}

void IterationLogic::moveResultTo(std::vector<Result>& results) noexcept {
    results.emplace_back(std::move(mPimpl->mResult));
}

#    if ANKERL_NANOBENCH(PERF_COUNTERS)

ANKERL_NANOBENCH(IGNORE_PADDED_PUSH)
class LinuxPerformanceCounters {
public:
    struct Target {
        Target(uint64_t* targetValue_, bool correctMeasuringOverhead_, bool correctLoopOverhead_)
            : targetValue(targetValue_)
            , correctMeasuringOverhead(correctMeasuringOverhead_)
            , correctLoopOverhead(correctLoopOverhead_) {}

        uint64_t* targetValue{};
        bool correctMeasuringOverhead{};
        bool correctLoopOverhead{};
    };

    ~LinuxPerformanceCounters();

    // quick operation
    inline void start() {}

    inline void stop() {}

    bool monitor(perf_sw_ids swId, Target target);
    bool monitor(perf_hw_id hwId, Target target);

    bool hasError() const noexcept {
        return mHasError;
    }

    // Just reading data is faster than enable & disabling.
    // we subtract data ourselves.
    inline void beginMeasure() {
        if (mHasError) {
            return;
        }

        // NOLINTNEXTLINE(hicpp-signed-bitwise)
        mHasError = -1 == ioctl(mFd, PERF_EVENT_IOC_RESET, PERF_IOC_FLAG_GROUP);
        if (mHasError) {
            return;
        }

        // NOLINTNEXTLINE(hicpp-signed-bitwise)
        mHasError = -1 == ioctl(mFd, PERF_EVENT_IOC_ENABLE, PERF_IOC_FLAG_GROUP);
    }

    inline void endMeasure() {
        if (mHasError) {
            return;
        }

        // NOLINTNEXTLINE(hicpp-signed-bitwise)
        mHasError = (-1 == ioctl(mFd, PERF_EVENT_IOC_DISABLE, PERF_IOC_FLAG_GROUP));
        if (mHasError) {
            return;
        }

        auto const numBytes = sizeof(uint64_t) * mCounters.size();
        auto ret = read(mFd, mCounters.data(), numBytes);
        mHasError = ret != static_cast<ssize_t>(numBytes);
    }

    void updateResults(uint64_t numIters);

    // rounded integer division
    template <typename T>
    static inline T divRounded(T a, T divisor) {
        return (a + divisor / 2) / divisor;
    }

    template <typename Op>
    ANKERL_NANOBENCH_NO_SANITIZE("integer", "undefined")
    void calibrate(Op&& op) {
        // clear current calibration data,
        for (auto& v : mCalibratedOverhead) {
            v = UINT64_C(0);
        }

        // create new calibration data
        auto newCalibration = mCalibratedOverhead;
        for (auto& v : newCalibration) {
            v = (std::numeric_limits<uint64_t>::max)();
        }
        for (size_t iter = 0; iter < 100; ++iter) {
            beginMeasure();
            op();
            endMeasure();
            if (mHasError) {
                return;
            }

            for (size_t i = 0; i < newCalibration.size(); ++i) {
                auto diff = mCounters[i];
                if (newCalibration[i] > diff) {
                    newCalibration[i] = diff;
                }
            }
        }

        mCalibratedOverhead = std::move(newCalibration);

        {
            // calibrate loop overhead. For branches & instructions this makes sense, not so much for everything else like cycles.
            // marsaglia's xorshift: mov, sal/shr, xor. Times 3.
            // This has the nice property that the compiler doesn't seem to be able to optimize multiple calls any further.
            // see https://godbolt.org/z/49RVQ5
            uint64_t const numIters = 100000U + (std::random_device{}() & 3);
            uint64_t n = numIters;
            uint32_t x = 1234567;
            auto fn = [&]() {
                x ^= x << 13;
                x ^= x >> 17;
                x ^= x << 5;
            };

            beginMeasure();
            while (n-- > 0) {
                fn();
            }
            endMeasure();
            detail::doNotOptimizeAway(x);
            auto measure1 = mCounters;

            n = numIters;
            beginMeasure();
            while (n-- > 0) {
                // we now run *twice* so we can easily calculate the overhead
                fn();
                fn();
            }
            endMeasure();
            detail::doNotOptimizeAway(x);
            auto measure2 = mCounters;

            for (size_t i = 0; i < mCounters.size(); ++i) {
                // factor 2 because we have two instructions per loop
                auto m1 = measure1[i] > mCalibratedOverhead[i] ? measure1[i] - mCalibratedOverhead[i] : 0;
                auto m2 = measure2[i] > mCalibratedOverhead[i] ? measure2[i] - mCalibratedOverhead[i] : 0;
                auto overhead = m1 * 2 > m2 ? m1 * 2 - m2 : 0;

                mLoopOverhead[i] = divRounded(overhead, numIters);
            }
        }
    }

private:
    bool monitor(uint32_t type, uint64_t eventid, Target target);

    std::map<uint64_t, Target> mIdToTarget{};

    // start with minimum size of 3 for read_format
    std::vector<uint64_t> mCounters{3};
    std::vector<uint64_t> mCalibratedOverhead{3};
    std::vector<uint64_t> mLoopOverhead{3};

    uint64_t mTimeEnabledNanos = 0;
    uint64_t mTimeRunningNanos = 0;
    int mFd = -1;
    bool mHasError = false;
};
ANKERL_NANOBENCH(IGNORE_PADDED_POP)

LinuxPerformanceCounters::~LinuxPerformanceCounters() {
    if (-1 != mFd) {
        close(mFd);
    }
}

bool LinuxPerformanceCounters::monitor(perf_sw_ids swId, LinuxPerformanceCounters::Target target) {
    return monitor(PERF_TYPE_SOFTWARE, swId, target);
}

bool LinuxPerformanceCounters::monitor(perf_hw_id hwId, LinuxPerformanceCounters::Target target) {
    return monitor(PERF_TYPE_HARDWARE, hwId, target);
}

// overflow is ok, it's checked
ANKERL_NANOBENCH_NO_SANITIZE("integer", "undefined")
void LinuxPerformanceCounters::updateResults(uint64_t numIters) {
    // clear old data
    for (auto& id_value : mIdToTarget) {
        *id_value.second.targetValue = UINT64_C(0);
    }

    if (mHasError) {
        return;
    }

    mTimeEnabledNanos = mCounters[1] - mCalibratedOverhead[1];
    mTimeRunningNanos = mCounters[2] - mCalibratedOverhead[2];

    for (uint64_t i = 0; i < mCounters[0]; ++i) {
        auto idx = static_cast<size_t>(3 + i * 2 + 0);
        auto id = mCounters[idx + 1U];

        auto it = mIdToTarget.find(id);
        if (it != mIdToTarget.end()) {

            auto& tgt = it->second;
            *tgt.targetValue = mCounters[idx];
            if (tgt.correctMeasuringOverhead) {
                if (*tgt.targetValue >= mCalibratedOverhead[idx]) {
                    *tgt.targetValue -= mCalibratedOverhead[idx];
                } else {
                    *tgt.targetValue = 0U;
                }
            }
            if (tgt.correctLoopOverhead) {
                auto correctionVal = mLoopOverhead[idx] * numIters;
                if (*tgt.targetValue >= correctionVal) {
                    *tgt.targetValue -= correctionVal;
                } else {
                    *tgt.targetValue = 0U;
                }
            }
        }
    }
}

bool LinuxPerformanceCounters::monitor(uint32_t type, uint64_t eventid, Target target) {
    *target.targetValue = (std::numeric_limits<uint64_t>::max)();
    if (mHasError) {
        return false;
    }

    auto pea = perf_event_attr();
    std::memset(&pea, 0, sizeof(perf_event_attr));
    pea.type = type;
    pea.size = sizeof(perf_event_attr);
    pea.config = eventid;
    pea.disabled = 1; // start counter as disabled
    pea.exclude_kernel = 1;
    pea.exclude_hv = 1;

    // NOLINTNEXTLINE(hicpp-signed-bitwise)
    pea.read_format = PERF_FORMAT_GROUP | PERF_FORMAT_ID | PERF_FORMAT_TOTAL_TIME_ENABLED | PERF_FORMAT_TOTAL_TIME_RUNNING;

    const int pid = 0;                    // the current process
    const int cpu = -1;                   // all CPUs
#        if defined(PERF_FLAG_FD_CLOEXEC) // since Linux 3.14
    const unsigned long flags = PERF_FLAG_FD_CLOEXEC;
#        else
    const unsigned long flags = 0;
#        endif

    auto fd = static_cast<int>(syscall(__NR_perf_event_open, &pea, pid, cpu, mFd, flags));
    if (-1 == fd) {
        return false;
    }
    if (-1 == mFd) {
        // first call: set to fd, and use this from now on
        mFd = fd;
    }
    uint64_t id = 0;
    // NOLINTNEXTLINE(hicpp-signed-bitwise)
    if (-1 == ioctl(fd, PERF_EVENT_IOC_ID, &id)) {
        // couldn't get id
        return false;
    }

    // insert into map, rely on the fact that map's references are constant.
    mIdToTarget.emplace(id, target);

    // prepare readformat with the correct size (after the insert)
    auto size = 3 + 2 * mIdToTarget.size();
    mCounters.resize(size);
    mCalibratedOverhead.resize(size);
    mLoopOverhead.resize(size);

    return true;
}

PerformanceCounters::PerformanceCounters()
    : mPc(new LinuxPerformanceCounters())
    , mVal()
    , mHas() {

    mHas.pageFaults = mPc->monitor(PERF_COUNT_SW_PAGE_FAULTS, LinuxPerformanceCounters::Target(&mVal.pageFaults, true, false));
    mHas.cpuCycles = mPc->monitor(PERF_COUNT_HW_REF_CPU_CYCLES, LinuxPerformanceCounters::Target(&mVal.cpuCycles, true, false));
    mHas.contextSwitches =
        mPc->monitor(PERF_COUNT_SW_CONTEXT_SWITCHES, LinuxPerformanceCounters::Target(&mVal.contextSwitches, true, false));
    mHas.instructions = mPc->monitor(PERF_COUNT_HW_INSTRUCTIONS, LinuxPerformanceCounters::Target(&mVal.instructions, true, true));
    mHas.branchInstructions =
        mPc->monitor(PERF_COUNT_HW_BRANCH_INSTRUCTIONS, LinuxPerformanceCounters::Target(&mVal.branchInstructions, true, false));
    mHas.branchMisses = mPc->monitor(PERF_COUNT_HW_BRANCH_MISSES, LinuxPerformanceCounters::Target(&mVal.branchMisses, true, false));
    // mHas.branchMisses = false;

    mPc->start();
    mPc->calibrate([] {
        auto before = ankerl::nanobench::Clock::now();
        auto after = ankerl::nanobench::Clock::now();
        (void)before;
        (void)after;
    });

    if (mPc->hasError()) {
        // something failed, don't monitor anything.
        mHas = PerfCountSet<bool>{};
    }
}

PerformanceCounters::~PerformanceCounters() {
    if (nullptr != mPc) {
        delete mPc;
    }
}

void PerformanceCounters::beginMeasure() {
    mPc->beginMeasure();
}

void PerformanceCounters::endMeasure() {
    mPc->endMeasure();
}

void PerformanceCounters::updateResults(uint64_t numIters) {
    mPc->updateResults(numIters);
}

#    else

PerformanceCounters::PerformanceCounters() = default;
PerformanceCounters::~PerformanceCounters() = default;
void PerformanceCounters::beginMeasure() {}
void PerformanceCounters::endMeasure() {}
void PerformanceCounters::updateResults(uint64_t) {}

#    endif

ANKERL_NANOBENCH(NODISCARD) PerfCountSet<uint64_t> const& PerformanceCounters::val() const noexcept {
    return mVal;
}
ANKERL_NANOBENCH(NODISCARD) PerfCountSet<bool> const& PerformanceCounters::has() const noexcept {
    return mHas;
}

// formatting utilities
namespace fmt {

// adds thousands separator to numbers
NumSep::NumSep(char sep)
    : mSep(sep) {}

char NumSep::do_thousands_sep() const {
    return mSep;
}

std::string NumSep::do_grouping() const {
    return "\003";
}

// RAII to save & restore a stream's state
StreamStateRestorer::StreamStateRestorer(std::ostream& s)
    : mStream(s)
    , mLocale(s.getloc())
    , mPrecision(s.precision())
    , mWidth(s.width())
    , mFill(s.fill())
    , mFmtFlags(s.flags()) {}

StreamStateRestorer::~StreamStateRestorer() {
    restore();
}

// sets back all stream info that we remembered at construction
void StreamStateRestorer::restore() {
    mStream.imbue(mLocale);
    mStream.precision(mPrecision);
    mStream.width(mWidth);
    mStream.fill(mFill);
    mStream.flags(mFmtFlags);
}

Number::Number(int width, int precision, int64_t value)
    : mWidth(width)
    , mPrecision(precision)
    , mValue(static_cast<double>(value)) {}

Number::Number(int width, int precision, double value)
    : mWidth(width)
    , mPrecision(precision)
    , mValue(value) {}

std::ostream& Number::write(std::ostream& os) const {
    StreamStateRestorer restorer(os);
    os.imbue(std::locale(os.getloc(), new NumSep(',')));
    os << std::setw(mWidth) << std::setprecision(mPrecision) << std::fixed << mValue;
    return os;
}

std::string Number::to_s() const {
    std::stringstream ss;
    write(ss);
    return ss.str();
}

std::string to_s(uint64_t n) {
    std::string str;
    do {
        str += static_cast<char>('0' + static_cast<char>(n % 10));
        n /= 10;
    } while (n != 0);
    std::reverse(str.begin(), str.end());
    return str;
}

std::ostream& operator<<(std::ostream& os, Number const& n) {
    return n.write(os);
}

MarkDownColumn::MarkDownColumn(int w, int prec, std::string const& tit, std::string const& suff, double val)
    : mWidth(w)
    , mPrecision(prec)
    , mTitle(tit)
    , mSuffix(suff)
    , mValue(val) {}

std::string MarkDownColumn::title() const {
    std::stringstream ss;
    ss << '|' << std::setw(mWidth - 2) << std::right << mTitle << ' ';
    return ss.str();
}

std::string MarkDownColumn::separator() const {
    std::string sep(static_cast<size_t>(mWidth), '-');
    sep.front() = '|';
    sep.back() = ':';
    return sep;
}

std::string MarkDownColumn::invalid() const {
    std::string sep(static_cast<size_t>(mWidth), ' ');
    sep.front() = '|';
    sep[sep.size() - 2] = '-';
    return sep;
}

std::string MarkDownColumn::value() const {
    std::stringstream ss;
    auto width = mWidth - 2 - static_cast<int>(mSuffix.size());
    ss << '|' << Number(width, mPrecision, mValue) << mSuffix << ' ';
    return ss.str();
}

// Formats any text as markdown code, escaping backticks.
MarkDownCode::MarkDownCode(std::string const& what) {
    mWhat.reserve(what.size() + 2);
    mWhat.push_back('`');
    for (char c : what) {
        mWhat.push_back(c);
        if ('`' == c) {
            mWhat.push_back('`');
        }
    }
    mWhat.push_back('`');
}

std::ostream& MarkDownCode::write(std::ostream& os) const {
    return os << mWhat;
}

std::ostream& operator<<(std::ostream& os, MarkDownCode const& mdCode) {
    return mdCode.write(os);
}
} // namespace fmt
} // namespace detail

// provide implementation here so it's only generated once
Config::Config() = default;
Config::~Config() = default;
Config& Config::operator=(Config const&) = default;
Config& Config::operator=(Config&&) = default;
Config::Config(Config const&) = default;
Config::Config(Config&&) noexcept = default;

// provide implementation here so it's only generated once
Result::~Result() = default;
Result& Result::operator=(Result const&) = default;
Result& Result::operator=(Result&&) = default;
Result::Result(Result const&) = default;
Result::Result(Result&&) noexcept = default;

namespace detail {
template <typename T>
inline constexpr typename std::underlying_type<T>::type u(T val) noexcept {
    return static_cast<typename std::underlying_type<T>::type>(val);
}
} // namespace detail

// Result returned after a benchmark has finished. Can be used as a baseline for relative().
Result::Result(Config const& benchmarkConfig)
    : mConfig(benchmarkConfig)
    , mNameToMeasurements{detail::u(Result::Measure::_size)} {}

void Result::add(Clock::duration totalElapsed, uint64_t iters, detail::PerformanceCounters const& pc) {
    using detail::d;
    using detail::u;

    double dIters = d(iters);
    mNameToMeasurements[u(Result::Measure::iterations)].push_back(dIters);

    mNameToMeasurements[u(Result::Measure::elapsed)].push_back(d(totalElapsed) / dIters);
    if (pc.has().pageFaults) {
        mNameToMeasurements[u(Result::Measure::pagefaults)].push_back(d(pc.val().pageFaults) / dIters);
    }
    if (pc.has().cpuCycles) {
        mNameToMeasurements[u(Result::Measure::cpucycles)].push_back(d(pc.val().cpuCycles) / dIters);
    }
    if (pc.has().contextSwitches) {
        mNameToMeasurements[u(Result::Measure::contextswitches)].push_back(d(pc.val().contextSwitches) / dIters);
    }
    if (pc.has().instructions) {
        mNameToMeasurements[u(Result::Measure::instructions)].push_back(d(pc.val().instructions) / dIters);
    }
    if (pc.has().branchInstructions) {
        double branchInstructions = 0.0;
        // correcting branches: remove branch introduced by the while (...) loop for each iteration.
        if (pc.val().branchInstructions > iters + 1U) {
            branchInstructions = d(pc.val().branchInstructions - (iters + 1U));
        }
        mNameToMeasurements[u(Result::Measure::branchinstructions)].push_back(branchInstructions / dIters);

        if (pc.has().branchMisses) {
            // correcting branch misses
            double branchMisses = d(pc.val().branchMisses);
            if (branchMisses > branchInstructions) {
                // can't have branch misses when there were branches...
                branchMisses = branchInstructions;
            }

            // assuming at least one missed branch for the loop
            branchMisses -= 1.0;
            if (branchMisses < 1.0) {
                branchMisses = 1.0;
            }
            mNameToMeasurements[u(Result::Measure::branchmisses)].push_back(branchMisses / dIters);
        }
    }
}

Config const& Result::config() const noexcept {
    return mConfig;
}

inline double calcMedian(std::vector<double>& data) {
    if (data.empty()) {
        return 0.0;
    }
    std::sort(data.begin(), data.end());

    auto midIdx = data.size() / 2U;
    if (1U == (data.size() & 1U)) {
        return data[midIdx];
    }
    return (data[midIdx - 1U] + data[midIdx]) / 2U;
}

double Result::median(Measure m) const {
    // create a copy so we can sort
    auto data = mNameToMeasurements[detail::u(m)];
    return calcMedian(data);
}

double Result::average(Measure m) const {
    using detail::d;
    auto const& data = mNameToMeasurements[detail::u(m)];
    if (data.empty()) {
        return 0.0;
    }

    // create a copy so we can sort
    return sum(m) / d(data.size());
}

double Result::medianAbsolutePercentError(Measure m) const {
    // create copy
    auto data = mNameToMeasurements[detail::u(m)];

    // calculates MdAPE which is the median of percentage error
    // see https://www.spiderfinancial.com/support/documentation/numxl/reference-manual/forecasting-performance/mdape
    auto med = calcMedian(data);

    // transform the data to absolute error
    for (auto& x : data) {
        x = (x - med) / x;
        if (x < 0) {
            x = -x;
        }
    }
    return calcMedian(data);
}

double Result::sum(Measure m) const noexcept {
    auto const& data = mNameToMeasurements[detail::u(m)];
    return std::accumulate(data.begin(), data.end(), 0.0);
}

double Result::sumProduct(Measure m1, Measure m2) const noexcept {
    auto const& data1 = mNameToMeasurements[detail::u(m1)];
    auto const& data2 = mNameToMeasurements[detail::u(m2)];

    if (data1.size() != data2.size()) {
        return 0.0;
    }

    double result = 0.0;
    for (size_t i = 0, s = data1.size(); i != s; ++i) {
        result += data1[i] * data2[i];
    }
    return result;
}

bool Result::has(Measure m) const noexcept {
    return !mNameToMeasurements[detail::u(m)].empty();
}

double Result::get(size_t idx, Measure m) const {
    auto const& data = mNameToMeasurements[detail::u(m)];
    return data.at(idx);
}

bool Result::empty() const noexcept {
    return 0U == size();
}

size_t Result::size() const noexcept {
    auto const& data = mNameToMeasurements[detail::u(Measure::elapsed)];
    return data.size();
}

double Result::minimum(Measure m) const noexcept {
    auto const& data = mNameToMeasurements[detail::u(m)];
    if (data.empty()) {
        return 0.0;
    }

    // here its save to assume that at least one element is there
    return *std::min_element(data.begin(), data.end());
}

double Result::maximum(Measure m) const noexcept {
    auto const& data = mNameToMeasurements[detail::u(m)];
    if (data.empty()) {
        return 0.0;
    }

    // here its save to assume that at least one element is there
    return *std::max_element(data.begin(), data.end());
}

Result::Measure Result::fromString(std::string const& str) {
    if (str == "elapsed") {
        return Measure::elapsed;
    } else if (str == "iterations") {
        return Measure::iterations;
    } else if (str == "pagefaults") {
        return Measure::pagefaults;
    } else if (str == "cpucycles") {
        return Measure::cpucycles;
    } else if (str == "contextswitches") {
        return Measure::contextswitches;
    } else if (str == "instructions") {
        return Measure::instructions;
    } else if (str == "branchinstructions") {
        return Measure::branchinstructions;
    } else if (str == "branchmisses") {
        return Measure::branchmisses;
    } else {
        // not found, return _size
        return Measure::_size;
    }
}

// Configuration of a microbenchmark.
Bench::Bench() {
    mConfig.mOut = &std::cout;
}

Bench::Bench(Bench&&) = default;
Bench& Bench::operator=(Bench&&) = default;
Bench::Bench(Bench const&) = default;
Bench& Bench::operator=(Bench const&) = default;
Bench::~Bench() noexcept = default;

double Bench::batch() const noexcept {
    return mConfig.mBatch;
}

double Bench::complexityN() const noexcept {
    return mConfig.mComplexityN;
}

// Set a baseline to compare it to. 100% it is exactly as fast as the baseline, >100% means it is faster than the baseline, <100%
// means it is slower than the baseline.
Bench& Bench::relative(bool isRelativeEnabled) noexcept {
    mConfig.mIsRelative = isRelativeEnabled;
    return *this;
}
bool Bench::relative() const noexcept {
    return mConfig.mIsRelative;
}

Bench& Bench::performanceCounters(bool showPerformanceCounters) noexcept {
    mConfig.mShowPerformanceCounters = showPerformanceCounters;
    return *this;
}
bool Bench::performanceCounters() const noexcept {
    return mConfig.mShowPerformanceCounters;
}

// Operation unit. Defaults to "op", could be e.g. "byte" for string processing.
// If u differs from currently set unit, the stored results will be cleared.
// Use singular (byte, not bytes).
Bench& Bench::unit(char const* u) {
    if (u != mConfig.mUnit) {
        mResults.clear();
    }
    mConfig.mUnit = u;
    return *this;
}

Bench& Bench::unit(std::string const& u) {
    return unit(u.c_str());
}

std::string const& Bench::unit() const noexcept {
    return mConfig.mUnit;
}

Bench& Bench::timeUnit(std::chrono::duration<double> const& tu, std::string const& tuName) {
    mConfig.mTimeUnit = tu;
    mConfig.mTimeUnitName = tuName;
    return *this;
}

std::string const& Bench::timeUnitName() const noexcept {
    return mConfig.mTimeUnitName;
}

std::chrono::duration<double> const& Bench::timeUnit() const noexcept {
    return mConfig.mTimeUnit;
}

// If benchmarkTitle differs from currently set title, the stored results will be cleared.
Bench& Bench::title(const char* benchmarkTitle) {
    if (benchmarkTitle != mConfig.mBenchmarkTitle) {
        mResults.clear();
    }
    mConfig.mBenchmarkTitle = benchmarkTitle;
    return *this;
}
Bench& Bench::title(std::string const& benchmarkTitle) {
    if (benchmarkTitle != mConfig.mBenchmarkTitle) {
        mResults.clear();
    }
    mConfig.mBenchmarkTitle = benchmarkTitle;
    return *this;
}

std::string const& Bench::title() const noexcept {
    return mConfig.mBenchmarkTitle;
}

Bench& Bench::name(const char* benchmarkName) {
    mConfig.mBenchmarkName = benchmarkName;
    return *this;
}

Bench& Bench::name(std::string const& benchmarkName) {
    mConfig.mBenchmarkName = benchmarkName;
    return *this;
}

std::string const& Bench::name() const noexcept {
    return mConfig.mBenchmarkName;
}

// Number of epochs to evaluate. The reported result will be the median of evaluation of each epoch.
Bench& Bench::epochs(size_t numEpochs) noexcept {
    mConfig.mNumEpochs = numEpochs;
    return *this;
}
size_t Bench::epochs() const noexcept {
    return mConfig.mNumEpochs;
}

// Desired evaluation time is a multiple of clock resolution. Default is to be 1000 times above this measurement precision.
Bench& Bench::clockResolutionMultiple(size_t multiple) noexcept {
    mConfig.mClockResolutionMultiple = multiple;
    return *this;
}
size_t Bench::clockResolutionMultiple() const noexcept {
    return mConfig.mClockResolutionMultiple;
}

// Sets the maximum time each epoch should take. Default is 100ms.
Bench& Bench::maxEpochTime(std::chrono::nanoseconds t) noexcept {
    mConfig.mMaxEpochTime = t;
    return *this;
}
std::chrono::nanoseconds Bench::maxEpochTime() const noexcept {
    return mConfig.mMaxEpochTime;
}

// Sets the maximum time each epoch should take. Default is 100ms.
Bench& Bench::minEpochTime(std::chrono::nanoseconds t) noexcept {
    mConfig.mMinEpochTime = t;
    return *this;
}
std::chrono::nanoseconds Bench::minEpochTime() const noexcept {
    return mConfig.mMinEpochTime;
}

Bench& Bench::minEpochIterations(uint64_t numIters) noexcept {
    mConfig.mMinEpochIterations = (numIters == 0) ? 1 : numIters;
    return *this;
}
uint64_t Bench::minEpochIterations() const noexcept {
    return mConfig.mMinEpochIterations;
}

Bench& Bench::epochIterations(uint64_t numIters) noexcept {
    mConfig.mEpochIterations = numIters;
    return *this;
}
uint64_t Bench::epochIterations() const noexcept {
    return mConfig.mEpochIterations;
}

Bench& Bench::warmup(uint64_t numWarmupIters) noexcept {
    mConfig.mWarmup = numWarmupIters;
    return *this;
}
uint64_t Bench::warmup() const noexcept {
    return mConfig.mWarmup;
}

Bench& Bench::config(Config const& benchmarkConfig) {
    mConfig = benchmarkConfig;
    return *this;
}
Config const& Bench::config() const noexcept {
    return mConfig;
}

Bench& Bench::output(std::ostream* outstream) noexcept {
    mConfig.mOut = outstream;
    return *this;
}

ANKERL_NANOBENCH(NODISCARD) std::ostream* Bench::output() const noexcept {
    return mConfig.mOut;
}

std::vector<Result> const& Bench::results() const noexcept {
    return mResults;
}

Bench& Bench::render(char const* templateContent, std::ostream& os) {
    ::ankerl::nanobench::render(templateContent, *this, os);
    return *this;
}

Bench& Bench::render(std::string const& templateContent, std::ostream& os) {
    ::ankerl::nanobench::render(templateContent, *this, os);
    return *this;
}

std::vector<BigO> Bench::complexityBigO() const {
    std::vector<BigO> bigOs;
    auto rangeMeasure = BigO::collectRangeMeasure(mResults);
    bigOs.emplace_back("O(1)", rangeMeasure, [](double) {
        return 1.0;
    });
    bigOs.emplace_back("O(n)", rangeMeasure, [](double n) {
        return n;
    });
    bigOs.emplace_back("O(log n)", rangeMeasure, [](double n) {
        return std::log2(n);
    });
    bigOs.emplace_back("O(n log n)", rangeMeasure, [](double n) {
        return n * std::log2(n);
    });
    bigOs.emplace_back("O(n^2)", rangeMeasure, [](double n) {
        return n * n;
    });
    bigOs.emplace_back("O(n^3)", rangeMeasure, [](double n) {
        return n * n * n;
    });
    std::sort(bigOs.begin(), bigOs.end());
    return bigOs;
}

Rng::Rng()
    : mX(0)
    , mY(0) {
    std::random_device rd;
    std::uniform_int_distribution<uint64_t> dist;
    do {
        mX = dist(rd);
        mY = dist(rd);
    } while (mX == 0 && mY == 0);
}

ANKERL_NANOBENCH_NO_SANITIZE("integer", "undefined")
uint64_t splitMix64(uint64_t& state) noexcept {
    uint64_t z = (state += UINT64_C(0x9e3779b97f4a7c15));
    z = (z ^ (z >> 30U)) * UINT64_C(0xbf58476d1ce4e5b9);
    z = (z ^ (z >> 27U)) * UINT64_C(0x94d049bb133111eb);
    return z ^ (z >> 31U);
}

// Seeded as described in romu paper (update april 2020)
Rng::Rng(uint64_t seed) noexcept
    : mX(splitMix64(seed))
    , mY(splitMix64(seed)) {
    for (size_t i = 0; i < 10; ++i) {
        operator()();
    }
}

// only internally used to copy the RNG.
Rng::Rng(uint64_t x, uint64_t y) noexcept
    : mX(x)
    , mY(y) {}

Rng Rng::copy() const noexcept {
    return Rng{mX, mY};
}

Rng::Rng(std::vector<uint64_t> const& data)
    : mX(0)
    , mY(0) {
    if (data.size() != 2) {
        throw std::runtime_error("ankerl::nanobench::Rng::Rng: needed exactly 2 entries in data, but got " +
                                 detail::fmt::to_s(data.size()));
    }
    mX = data[0];
    mY = data[1];
}

std::vector<uint64_t> Rng::state() const {
    std::vector<uint64_t> data(2);
    data[0] = mX;
    data[1] = mY;
    return data;
}

BigO::RangeMeasure BigO::collectRangeMeasure(std::vector<Result> const& results) {
    BigO::RangeMeasure rangeMeasure;
    for (auto const& result : results) {
        if (result.config().mComplexityN > 0.0) {
            rangeMeasure.emplace_back(result.config().mComplexityN, result.median(Result::Measure::elapsed));
        }
    }
    return rangeMeasure;
}

BigO::BigO(std::string const& bigOName, RangeMeasure const& rangeMeasure)
    : mName(bigOName) {

    // estimate the constant factor
    double sumRangeMeasure = 0.0;
    double sumRangeRange = 0.0;

    for (size_t i = 0; i < rangeMeasure.size(); ++i) {
        sumRangeMeasure += rangeMeasure[i].first * rangeMeasure[i].second;
        sumRangeRange += rangeMeasure[i].first * rangeMeasure[i].first;
    }
    mConstant = sumRangeMeasure / sumRangeRange;

    // calculate root mean square
    double err = 0.0;
    double sumMeasure = 0.0;
    for (size_t i = 0; i < rangeMeasure.size(); ++i) {
        auto diff = mConstant * rangeMeasure[i].first - rangeMeasure[i].second;
        err += diff * diff;

        sumMeasure += rangeMeasure[i].second;
    }

    auto n = static_cast<double>(rangeMeasure.size());
    auto mean = sumMeasure / n;
    mNormalizedRootMeanSquare = std::sqrt(err / n) / mean;
}

BigO::BigO(const char* bigOName, RangeMeasure const& rangeMeasure)
    : BigO(std::string(bigOName), rangeMeasure) {}

std::string const& BigO::name() const noexcept {
    return mName;
}

double BigO::constant() const noexcept {
    return mConstant;
}

double BigO::normalizedRootMeanSquare() const noexcept {
    return mNormalizedRootMeanSquare;
}

bool BigO::operator<(BigO const& other) const noexcept {
    return std::tie(mNormalizedRootMeanSquare, mName) < std::tie(other.mNormalizedRootMeanSquare, other.mName);
}

std::ostream& operator<<(std::ostream& os, BigO const& bigO) {
    return os << bigO.constant() << " * " << bigO.name() << ", rms=" << bigO.normalizedRootMeanSquare();
}

std::ostream& operator<<(std::ostream& os, std::vector<ankerl::nanobench::BigO> const& bigOs) {
    detail::fmt::StreamStateRestorer restorer(os);
    os << std::endl << "|   coefficient |   err% | complexity" << std::endl << "|--------------:|-------:|------------" << std::endl;
    for (auto const& bigO : bigOs) {
        os << "|" << std::setw(14) << std::setprecision(7) << std::scientific << bigO.constant() << " ";
        os << "|" << detail::fmt::Number(6, 1, bigO.normalizedRootMeanSquare() * 100.0) << "% ";
        os << "| " << bigO.name();
        os << std::endl;
    }
    return os;
}

} // namespace nanobench
} // namespace ankerl

#endif // ANKERL_NANOBENCH_IMPLEMENT
#endif // ANKERL_NANOBENCH_H_INCLUDED