absl/random/uniform_int_distribution_test.cc

// Copyright 2017 The Abseil Authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//      https://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

#include "absl/random/uniform_int_distribution.h"

#include <cmath>
#include <cstddef>
#include <cstdint>
#include <iterator>
#include <limits>
#include <random>
#include <sstream>
#include <string>
#include <vector>

#include "gmock/gmock.h"
#include "gtest/gtest.h"
#include "absl/log/log.h"
#include "absl/random/internal/chi_square.h"
#include "absl/random/internal/distribution_test_util.h"
#include "absl/random/internal/pcg_engine.h"
#include "absl/random/internal/sequence_urbg.h"
#include "absl/random/random.h"
#include "absl/strings/str_cat.h"

namespace {

template <typename IntType>
class UniformIntDistributionTest : public ::testing::Test {};

using IntTypes = ::testing::Types<int8_t, uint8_t, int16_t, uint16_t, int32_t,
                                  uint32_t, int64_t, uint64_t>;
TYPED_TEST_SUITE(UniformIntDistributionTest, IntTypes);

TYPED_TEST(UniformIntDistributionTest, ParamSerializeTest) {
  // This test essentially ensures that the parameters serialize,
  // not that the values generated cover the full range.
  using Limits = std::numeric_limits<TypeParam>;
  using param_type =
      typename absl::uniform_int_distribution<TypeParam>::param_type;
  const TypeParam kMin = std::is_unsigned_v<TypeParam> ? 37 : -105;
  const TypeParam kNegOneOrZero = std::is_unsigned_v<TypeParam> ? 0 : -1;

  constexpr int kCount = 1000;
  absl::InsecureBitGen gen;
  for (const auto& param : {
           param_type(),
           param_type(2, 2),  // Same
           param_type(9, 32),
           param_type(kMin, 115),
           param_type(kNegOneOrZero, Limits::max()),
           param_type(Limits::min(), Limits::max()),
           param_type(Limits::lowest(), Limits::max()),
           param_type(Limits::min() + 1, Limits::max() - 1),
       }) {
    const auto a = param.a();
    const auto b = param.b();
    absl::uniform_int_distribution<TypeParam> before(a, b);
    EXPECT_EQ(before.a(), param.a());
    EXPECT_EQ(before.b(), param.b());

    {
      // Initialize via param_type
      absl::uniform_int_distribution<TypeParam> via_param(param);
      EXPECT_EQ(via_param, before);
    }

    // Initialize via iostreams
    std::stringstream ss;
    ss << before;

    absl::uniform_int_distribution<TypeParam> after(Limits::min() + 3,
                                                    Limits::max() - 5);

    EXPECT_NE(before.a(), after.a());
    EXPECT_NE(before.b(), after.b());
    EXPECT_NE(before.param(), after.param());
    EXPECT_NE(before, after);

    ss >> after;

    EXPECT_EQ(before.a(), after.a());
    EXPECT_EQ(before.b(), after.b());
    EXPECT_EQ(before.param(), after.param());
    EXPECT_EQ(before, after);

    // Smoke test.
    auto sample_min = after.max();
    auto sample_max = after.min();
    for (int i = 0; i < kCount; i++) {
      auto sample = after(gen);
      EXPECT_GE(sample, after.min());
      EXPECT_LE(sample, after.max());
      if (sample > sample_max) {
        sample_max = sample;
      }
      if (sample < sample_min) {
        sample_min = sample;
      }
    }
    LOG(INFO) << "Range: " << sample_min << ", " << sample_max;
  }
}

TYPED_TEST(UniformIntDistributionTest, ViolatesPreconditionsDeathTest) {
#if GTEST_HAS_DEATH_TEST
  // Hi < Lo
  EXPECT_DEBUG_DEATH(
      { absl::uniform_int_distribution<TypeParam> dist(10, 1); }, "");
#endif  // GTEST_HAS_DEATH_TEST
#if defined(NDEBUG)
  // opt-mode, for invalid parameters, will generate a garbage value,
  // but should not enter an infinite loop.
  absl::InsecureBitGen gen;
  absl::uniform_int_distribution<TypeParam> dist(10, 1);
  auto x = dist(gen);

  // Any value will generate a non-empty string.
  EXPECT_FALSE(absl::StrCat(+x).empty()) << x;
#endif  // NDEBUG
}

TYPED_TEST(UniformIntDistributionTest, TestMoments) {
  constexpr int kSize = 100000;
  using Limits = std::numeric_limits<TypeParam>;
  using param_type =
      typename absl::uniform_int_distribution<TypeParam>::param_type;

  // We use a fixed bit generator for distribution accuracy tests.  This allows
  // these tests to be deterministic, while still testing the quality of the
  // implementation.
  absl::random_internal::pcg64_2018_engine rng{0x2B7E151628AED2A6};

  std::vector<double> values(kSize);
  for (const auto& param :
       {param_type(0, Limits::max()), param_type(13, 127)}) {
    absl::uniform_int_distribution<TypeParam> dist(param);
    for (int i = 0; i < kSize; i++) {
      const auto sample = dist(rng);
      ASSERT_LE(dist.param().a(), sample);
      ASSERT_GE(dist.param().b(), sample);
      values[i] = sample;
    }

    auto moments = absl::random_internal::ComputeDistributionMoments(values);
    const double a = dist.param().a();
    const double b = dist.param().b();
    const double n = (b - a + 1);
    const double mean = (a + b) / 2;
    const double var = ((b - a + 1) * (b - a + 1) - 1) / 12;
    const double kurtosis = 3 - 6 * (n * n + 1) / (5 * (n * n - 1));

    // TODO(ahh): this is not the right bound
    // empirically validated with --runs_per_test=10000.
    EXPECT_NEAR(mean, moments.mean, 0.01 * var);
    EXPECT_NEAR(var, moments.variance, 0.015 * var);
    EXPECT_NEAR(0.0, moments.skewness, 0.025);
    EXPECT_NEAR(kurtosis, moments.kurtosis, 0.02 * kurtosis);
  }
}

TYPED_TEST(UniformIntDistributionTest, ChiSquaredTest50) {
  using absl::random_internal::kChiSquared;

  constexpr size_t kTrials = 1000;
  constexpr int kBuckets = 50;  // inclusive, so actually +1
  constexpr double kExpected =
      static_cast<double>(kTrials) / static_cast<double>(kBuckets);

  // Empirically validated with --runs_per_test=10000.
  const int kThreshold =
      absl::random_internal::ChiSquareValue(kBuckets, 0.999999);

  const TypeParam min = std::is_unsigned_v<TypeParam> ? 37 : -37;
  const TypeParam max = min + kBuckets;

  // We use a fixed bit generator for distribution accuracy tests.  This allows
  // these tests to be deterministic, while still testing the quality of the
  // implementation.
  absl::random_internal::pcg64_2018_engine rng{0x2B7E151628AED2A6};

  absl::uniform_int_distribution<TypeParam> dist(min, max);

  std::vector<int32_t> counts(kBuckets + 1, 0);
  for (size_t i = 0; i < kTrials; i++) {
    auto x = dist(rng);
    counts[x - min]++;
  }
  double chi_square = absl::random_internal::ChiSquareWithExpected(
      std::begin(counts), std::end(counts), kExpected);
  if (chi_square > kThreshold) {
    double p_value =
        absl::random_internal::ChiSquarePValue(chi_square, kBuckets);

    // Chi-squared test failed. Output does not appear to be uniform.
    std::string msg;
    for (const auto& a : counts) {
      absl::StrAppend(&msg, a, "\n");
    }
    absl::StrAppend(&msg, kChiSquared, " p-value ", p_value, "\n");
    absl::StrAppend(&msg, "High ", kChiSquared, " value: ", chi_square, " > ",
                    kThreshold);
    LOG(INFO) << msg;
    FAIL() << msg;
  }
}

TEST(UniformIntDistributionTest, StabilityTest) {
  // absl::uniform_int_distribution stability relies only on integer operations.
  absl::random_internal::sequence_urbg urbg(
      {0x0003eb76f6f7f755ull, 0xFFCEA50FDB2F953Bull, 0xC332DDEFBE6C5AA5ull,
       0x6558218568AB9702ull, 0x2AEF7DAD5B6E2F84ull, 0x1521B62829076170ull,
       0xECDD4775619F1510ull, 0x13CCA830EB61BD96ull, 0x0334FE1EAA0363CFull,
       0xB5735C904C70A239ull, 0xD59E9E0BCBAADE14ull, 0xEECC86BC60622CA7ull});

  std::vector<int> output(12);

  {
    absl::uniform_int_distribution<int32_t> dist(0, 4);
    for (auto& v : output) {
      v = dist(urbg);
    }
  }
  EXPECT_EQ(12, urbg.invocations());
  EXPECT_THAT(output, testing::ElementsAre(4, 4, 3, 2, 1, 0, 1, 4, 3, 1, 3, 1));

  {
    urbg.reset();
    absl::uniform_int_distribution<int32_t> dist(0, 100);
    for (auto& v : output) {
      v = dist(urbg);
    }
  }
  EXPECT_EQ(12, urbg.invocations());
  EXPECT_THAT(output, testing::ElementsAre(97, 86, 75, 41, 36, 16, 38, 92, 67,
                                           30, 80, 38));

  {
    urbg.reset();
    absl::uniform_int_distribution<int32_t> dist(0, 10000);
    for (auto& v : output) {
      v = dist(urbg);
    }
  }
  EXPECT_EQ(12, urbg.invocations());
  EXPECT_THAT(output, testing::ElementsAre(9648, 8562, 7439, 4089, 3571, 1602,
                                           3813, 9195, 6641, 2986, 7956, 3765));
}

}  // namespace