bench.cpp

#include <algorithm>
#include <array>
#include <concepts>
#include <cstdint>
#include <cstring>
#include <iterator>
#include <numeric>
#include <print>
#include <span>
#include <vector>

void a(std::vector<std::uint8_t>& v, std::span<std::uint8_t> s);
void b(std::vector<std::uint8_t>& v, std::span<std::uint8_t> s);
void c(std::vector<std::uint8_t>& v, std::span<std::uint8_t> s);
void d(std::vector<std::uint8_t>& v, std::span<std::uint8_t> s);

int main(int argc, char* argv[]) {
  if(argc < 2) {
    std::println("Need arg");
    std::exit(EXIT_FAILURE);
  }

  char arg = *argv[1];

  std::vector<std::uint8_t> vec;
  vec.reserve(4096);
  std::array<std::uint32_t, 1024> arr;
  std::iota(arr.begin(), arr.end(), 0);

  std::span<std::uint8_t> sp {reinterpret_cast<std::uint8_t*>(arr.data()),
      sizeof(arr)};

  auto bench = [&](auto func) {
    for(size_t i {0}; i < 65536; ++i) {
      func(vec, sp);
      vec.clear();
    }
    std::exit(EXIT_SUCCESS);
  };

  switch(arg) {
    case 'a':
      bench(a);
    case 'b':
      bench(b);
    case 'c':
      bench(c);
    case 'd':
      bench(d);
  }

  std::println("Unknown arg");
  std::exit(EXIT_FAILURE);
}

funcs.cpp

#include <algorithm>
#include <array>
#include <concepts>
#include <cstdint>
#include <cstring>
#include <iterator>
#include <numeric>
#include <print>
#include <span>
#include <vector>

void a(std::vector<std::uint8_t>& v, std::span<std::uint8_t> s) {
  auto next = v.size();
  v.resize(v.size() + s.size());
  std::memcpy(v.data() + next, s.data(), s.size());
}

void b(std::vector<std::uint8_t>& v, std::span<std::uint8_t> s) {
  auto next = v.size();
  v.resize(v.size() + s.size());
  std::ranges::copy(s, v.begin() + next);
}

void c(std::vector<std::uint8_t>& v, std::span<std::uint8_t> s) {
  std::copy(s.begin(), s.end(), std::back_inserter(v));
}

void d(std::vector<std::uint8_t>& v, std::span<std::uint8_t> s) {
  std::ranges::copy(s, std::back_inserter(v));
}