add lehmer64 rng

This commit is contained in:
NukeBird 2025-03-09 23:28:43 +03:00
parent f523f1c521
commit 72da4beff0
2 changed files with 228 additions and 1 deletions

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@ -1,4 +1,74 @@
#include <array>
#include <bit>
#include <random>
#include <regex>
namespace s2ga
{
template<class... T>
struct always_false: std::false_type
{
};
class lehmer64
{
public:
lehmer64(__uint128_t seed = 0)
{
this->seed(seed);
}
void seed(__uint128_t z)
{
if(z == 0)
{
z = 0xC0FFEE;
}
s = z;
}
uint64_t operator()() noexcept
{
s *= 0xda942042e4dd58b5;
return s >> 64;
}
static constexpr uint64_t min()
{
return 0;
}
static constexpr uint64_t max()
{
return UINT64_MAX;
}
template<typename T>
T random(T min, T max)
{
if constexpr(std::is_integral_v<T>)
{
return std::uniform_int_distribution<T>(min, max)(*this);
}
else if constexpr(std::is_floating_point_v<T>)
{
return std::uniform_real_distribution<T>(min, max)(*this);
}
else
{
static_assert(always_false<T>::value,
"unsupported distribution type");
}
}
private:
__uint128_t s;
};
static_assert(std::uniform_random_bit_generator<lehmer64>);
}; // namespace s2ga
inline void foo() inline void foo()
{ {
} }

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@ -1,15 +1,172 @@
#include "../s2ga.hpp" #include "../s2ga.hpp"
#include <catch2/benchmark/catch_benchmark.hpp>
#include <catch2/catch_all.hpp> #include <catch2/catch_all.hpp>
#include <catch2/catch_approx.hpp> #include <catch2/catch_approx.hpp>
#include <catch2/catch_test_macros.hpp> #include <catch2/catch_test_macros.hpp>
#include <catch2/matchers/catch_matchers_range_equals.hpp> #include <catch2/matchers/catch_matchers_range_equals.hpp>
#include <cmath> #include <cmath>
#include <numbers> #include <numbers>
#include <random>
#include <vector>
using namespace Catch; using namespace Catch;
constexpr double TOLERANCE = 1e-4; constexpr double TOLERANCE = 1e-4;
TEST_CASE("lehmer64 rng")
{
s2ga::lehmer64 rng(0);
REQUIRE(rng() != 0);
const int N = 100;
{
std::vector<int> ivalues;
rng.seed(4);
for(int i = 0; i < N; ++i)
{
ivalues.emplace_back(rng.random(0, 256));
}
rng.seed(4);
for(int i = 0; i < N; ++i)
{
REQUIRE(ivalues[i] == rng.random(0, 256));
}
}
{
std::vector<float> fvalues;
rng.seed(5);
for(int i = 0; i < N; ++i)
{
fvalues.emplace_back(rng.random(-256.0f, 256.0f));
}
rng.seed(5);
for(int i = 0; i < N; ++i)
{
REQUIRE(fvalues[i] == rng.random(-256.0f, 256.0f));
}
}
}
TEST_CASE("Uniform Distribution Tests")
{
s2ga::lehmer64 rng(42); // Fixed seed for reproducibility
SECTION("Integer Uniformity - Chi-Squared Test")
{
const int min = 0;
const int max = 9;
const int num_samples = 1'000'000;
const int num_bins = max - min + 1;
const double expected = num_samples / static_cast<double>(num_bins);
const double critical_value = 16.92; // χ²(0.05, 9)
std::vector<int> counts(num_bins, 0);
for(int i = 0; i < num_samples; ++i)
{
int val = rng.random(min, max);
++counts[val - min];
}
double chi_sq = 0.0;
for(int count: counts)
{
double diff = count - expected;
chi_sq += (diff * diff) / expected;
}
CHECK(chi_sq < critical_value);
}
SECTION("Floating Point Uniformity - Kolmogorov-Smirnov Test")
{
const double min = 0.0;
const double max = 1.0;
const int num_samples = 100'000;
const double ks_critical = 1.36 / std::sqrt(num_samples); // α=0.05
std::vector<double> samples(num_samples);
std::generate(samples.begin(), samples.end(),
[&] { return rng.random(min, max); });
std::sort(samples.begin(), samples.end());
double d_plus = 0.0;
double d_minus = 0.0;
for(size_t i = 0; i < samples.size(); ++i)
{
double fn = (i + 1.0) / num_samples;
double f = samples[i];
d_plus = std::max(d_plus, fn - f);
d_minus = std::max(d_minus, f - (i / (num_samples - 1.0)));
}
double d_stat = std::max(d_plus, d_minus);
CHECK(d_stat < ks_critical);
}
SECTION("Edge Case Coverage")
{
const int iterations = 10'000;
// Test minimum and maximum inclusion
bool hit_min = false;
bool hit_max = false;
for(int i = 0; i < iterations; ++i)
{
int val = rng.random(1, 10);
if(val == 1)
hit_min = true;
if(val == 10)
hit_max = true;
}
CHECK(hit_min);
CHECK(hit_max);
// Floating point bounds check
for(int i = 0; i < iterations; ++i)
{
double val = rng.random(0.0, 1.0);
CHECK(val >= 0.0);
CHECK(val < 1.0);
}
}
}
TEST_CASE("random benchmarking", "[benchmark]")
{
s2ga::lehmer64 rng(0);
const int N = 100'000'000;
std::mt19937 std_rng(4);
std::uniform_int_distribution dist(-512, 512);
BENCHMARK("mt19937 100'000'000")
{
for(int i = 0; i < N; ++i)
{
(void)dist(std_rng);
}
};
BENCHMARK("lehmer64 100'000'000")
{
for(int i = 0; i < N; ++i)
{
(void)dist(rng);
}
};
}
inline double sphere(double x, double y) inline double sphere(double x, double y)
{ {
return std::pow(x, 2.0) + std::pow(y, 2.0); return std::pow(x, 2.0) + std::pow(y, 2.0);