cpp-shared-random-generator/test/distribution_test.cxx

//
//  distribution_test.cxx
//  shared_random_generator-test
//
//  Created by Sam Jaffe on 3/25/23.
//  Copyright © 2023 Sam Jaffe. All rights reserved.
//

#include <random/distribution.h>

#include <random/random.h>

#include "xcode_gtest_helper.h"

using testing::DoubleNear;

using engine::random::Random;
using engine::random::Uniform;

class kahan_summation {
private:
  double sum_{0.0};
  double carry_{0.0};

public:
  kahan_summation() = default;
  kahan_summation & operator+=(double d);

  explicit operator double() const { return sum_; }
};

kahan_summation & kahan_summation::operator+=(double num) {
  double const yield = num - carry_;
  double const total = sum_ + yield;
  carry_ = (total - sum_) - yield;
  sum_ = total;
  return *this;
}

TEST(UniformIntTest, UniformOnDefaultRandom) {
  Random generator{};
  kahan_summation sum{};
  size_t const iters = 2000000;
  for (size_t i = 0; i < iters; ++i) {
    // All values from 0 - 100 are allowable
    sum += generator(Uniform(0, 100));
  }
  // Expected result is (0+99)/2 +/- 0.1%
  EXPECT_THAT(double(sum) / iters, DoubleNear(50, 0.05));
}

TEST(UniformIntTest, IsClosed) {
  EXPECT_THAT(to_string(Uniform(0, 10)), "iUniform[0,10]");
}

TEST(UniformRealTest, UniformOnDefaultRandom) {
  Random generator{};
  kahan_summation sum{};
  size_t const iters = 2000000;
  for (size_t i = 0; i < iters; ++i) {
    // All values from 0 - 99 are allowable
    sum += generator(Uniform(0.0, 100.0));
  }
  // Expected result is [0.0, 100.0) +/- 0.1%
  EXPECT_THAT(double(sum) / iters, DoubleNear(50, 0.05));
}

TEST(UniformRealTest, IsOpen) {
  EXPECT_THAT(to_string(Uniform(0., 10.)), "dUniform[0,10)");
}