add benchmark code to the repo

Author: strega-nil

benchmarks/CMakeLists.txt

@@ -71,7 +71,5 @@ function(add_benchmark name)
     target_link_libraries(benchmark-${name} PRIVATE benchmark::benchmark)
 endfunction()
 
-add_benchmark(std_copy
-    src/std_copy.cpp
-    CXX_STANDARD 23
-)
+add_benchmark(std_copy src/std_copy.cpp)
+add_benchmark(random_integer_generation src/random_integer_generation.cpp)

benchmarks/src/random_integer_generation.cpp

@@ -0,0 +1,98 @@
+#include <benchmark/benchmark.h>
+#include <random>
+
+/// Test URBGs alone
+
+static void BM_mt19937(benchmark::State& state) {
+    std::mt19937 gen;
+    for (auto _ : state) {
+        benchmark::DoNotOptimize(gen());
+    }
+}
+BENCHMARK(BM_mt19937);
+
+static void BM_mt19937_64(benchmark::State& state) {
+    std::mt19937_64 gen;
+    for (auto _ : state) {
+        benchmark::DoNotOptimize(gen());
+    }
+}
+BENCHMARK(BM_mt19937_64);
+
+static void BM_lcg(benchmark::State& state) {
+    std::minstd_rand gen;
+    for (auto _ : state) {
+        benchmark::DoNotOptimize(gen());
+    }
+}
+BENCHMARK(BM_lcg);
+
+uint32_t GetMax() {
+    std::random_device gen;
+    std::uniform_int_distribution<uint32_t> dist(10'000'000, 20'000'000);
+    return dist(gen);
+}
+
+static const uint32_t max = GetMax(); // random divisor to prevent strength reduction
+
+/// Test mt19937
+
+static void BM_raw_mt19937_old(benchmark::State& state) {
+    std::mt19937 gen;
+    std::_Rng_from_urng<uint32_t, decltype(gen)> rng(gen);
+    for (auto _ : state) {
+        benchmark::DoNotOptimize(rng(max));
+    }
+}
+BENCHMARK(BM_raw_mt19937_old);
+
+static void BM_raw_mt19937_new(benchmark::State& state) {
+    std::mt19937 gen;
+    std::_Rng_from_urng_v2<uint32_t, decltype(gen)> rng(gen);
+    for (auto _ : state) {
+        benchmark::DoNotOptimize(rng(max));
+    }
+}
+BENCHMARK(BM_raw_mt19937_new);
+
+/// Test mt19937_64
+
+static void BM_raw_mt19937_64_old(benchmark::State& state) {
+    std::mt19937_64 gen;
+    std::_Rng_from_urng<uint64_t, decltype(gen)> rng(gen);
+    for (auto _ : state) {
+        benchmark::DoNotOptimize(rng(max));
+    }
+}
+BENCHMARK(BM_raw_mt19937_64_old);
+
+static void BM_raw_mt19937_64_new(benchmark::State& state) {
+    std::mt19937_64 gen;
+    std::_Rng_from_urng_v2<uint64_t, decltype(gen)> rng(gen);
+    for (auto _ : state) {
+        benchmark::DoNotOptimize(rng(max));
+    }
+}
+BENCHMARK(BM_raw_mt19937_64_new);
+
+/// Test minstd_rand
+
+static void BM_raw_lcg_old(benchmark::State& state) {
+    std::minstd_rand gen;
+    std::_Rng_from_urng<uint32_t, decltype(gen)> rng(gen);
+    for (auto _ : state) {
+        benchmark::DoNotOptimize(rng(max));
+    }
+}
+BENCHMARK(BM_raw_lcg_old);
+
+static void BM_raw_lcg_new(benchmark::State& state) {
+    std::minstd_rand gen;
+    std::_Rng_from_urng_v2<uint32_t, decltype(gen)> rng(gen);
+    for (auto _ : state) {
+        benchmark::DoNotOptimize(rng(max));
+    }
+}
+BENCHMARK(BM_raw_lcg_new);
+
+BENCHMARK_MAIN();

stl/inc/random

@@ -1844,9 +1844,7 @@ private:
 
     template <class _Engine>
     result_type _Eval(_Engine& _Eng, _Ty _Min, _Ty _Max) const { // compute next value in range [_Min, _Max]
-        conditional_t<_Has_static_min_max<_Engine>::value, _Rng_from_urng_v2<_Uty, _Engine>,
-            _Rng_from_urng<_Uty, _Engine>>
-            _Generator(_Eng);
+        _Rng_from_urng<_Uty, _Engine> _Generator(_Eng);
 
         const _Uty _Umin = _Adjust(static_cast<_Uty>(_Min));
         const _Uty _Umax = _Adjust(static_cast<_Uty>(_Max));
@@ -1864,7 +1862,7 @@ private:
 
     static _Uty _Adjust(_Uty _Uval) { // convert signed ranges to unsigned ranges and vice versa
         if constexpr (is_signed_v<_Ty>) {
-            constexpr _Uty _Adjuster = (static_cast<_Uty>(-1) >> 1) + 1; // 2^(N-1)
+            const _Uty _Adjuster = (static_cast<_Uty>(-1) >> 1) + 1; // 2^(N-1)
 
             if (_Uval < _Adjuster) {
                 return static_cast<_Uty>(_Uval + _Adjuster);