gistfile1.txt

#include <benchmark/benchmark.h>
#include <fmt/chrono.h>
#include <fmt/compile.h>

#include <ctime>

static void year_month_day_strftime(benchmark::State& state) {
  srand(0);
  tm t;
  t.tm_year = rand() % 10000 - 1900;
  t.tm_mon = rand() % 12 + 1;
  t.tm_mday = rand() % 31;
  t.tm_hour = rand() % 24;
  t.tm_min = rand() % 60;
  t.tm_sec = rand() % 60;
  for (auto _ : state) {
    char buf[10] = {};
    std::strftime(buf, 10, "%F", &t);
    benchmark::DoNotOptimize(buf);
  }
}
BENCHMARK(year_month_day_strftime);

static void year_month_day_fmt(benchmark::State& state) {
  srand(0);
  tm t;
  t.tm_year = rand() % 10000 - 1900;
  t.tm_mon = rand() % 12 + 1;
  t.tm_mday = rand() % 31;
  t.tm_hour = rand() % 24;
  t.tm_min = rand() % 60;
  t.tm_sec = rand() % 60;
  for (auto _ : state) {
    char buf[10] = {};
    fmt::format_to(buf, FMT_COMPILE("{:%F}"), t);
    benchmark::DoNotOptimize(buf);
  }
}
BENCHMARK(year_month_day_fmt);

BENCHMARK_MAIN();

--- 

Before:

2021-09-10 07:56:39
Running ./a.out
Run on (8 X 2300 MHz CPU s)
CPU Caches:
  L1 Data 49K (x4)
  L1 Instruction 32K (x4)
  L2 Unified 524K (x4)
  L3 Unified 8388K (x1)
Load Average: 2.92, 3.31, 3.36
------------------------------------------------------------------
Benchmark                        Time             CPU   Iterations
------------------------------------------------------------------
year_month_day_strftime        336 ns          336 ns      2002781
year_month_day_fmt             360 ns          360 ns      1992616

After:

 % c++ test.cc -I benchmark/include -I include -std=c++17 src/format.cc benchmark/src/libbenchmark.a -DNDEBUG -O3 -march=native && ./a.out
2021-09-10 07:53:40
Running ./a.out
Run on (8 X 2300 MHz CPU s)
CPU Caches:
  L1 Data 49K (x4)
  L1 Instruction 32K (x4)
  L2 Unified 524K (x4)
  L3 Unified 8388K (x1)
Load Average: 1.99, 3.82, 3.53
------------------------------------------------------------------
Benchmark                        Time             CPU   Iterations
------------------------------------------------------------------
year_month_day_strftime        337 ns          337 ns      2036612
year_month_day_fmt            4.93 ns         4.93 ns    135893304