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-rw-r--r--absl/random/internal/pool_urbg_test.cc182
1 files changed, 182 insertions, 0 deletions
diff --git a/absl/random/internal/pool_urbg_test.cc b/absl/random/internal/pool_urbg_test.cc
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+// 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/internal/pool_urbg.h"
+
+#include <algorithm>
+#include <bitset>
+#include <cmath>
+#include <cstdint>
+#include <iterator>
+
+#include "gtest/gtest.h"
+#include "absl/meta/type_traits.h"
+#include "absl/types/span.h"
+
+using absl::random_internal::PoolURBG;
+using absl::random_internal::RandenPool;
+
+namespace {
+
+// is_randen_pool trait is true when parameterized by an RandenPool
+template <typename T>
+using is_randen_pool = typename absl::disjunction<  //
+    std::is_same<T, RandenPool<uint8_t>>,           //
+    std::is_same<T, RandenPool<uint16_t>>,          //
+    std::is_same<T, RandenPool<uint32_t>>,          //
+    std::is_same<T, RandenPool<uint64_t>>>;         //
+
+// MyFill either calls RandenPool::Fill() or std::generate(..., rng)
+template <typename T, typename V>
+typename absl::enable_if_t<absl::negation<is_randen_pool<T>>::value, void>  //
+MyFill(T& rng, absl::Span<V> data) {  // NOLINT(runtime/references)
+  std::generate(std::begin(data), std::end(data), rng);
+}
+
+template <typename T, typename V>
+typename absl::enable_if_t<is_randen_pool<T>::value, void>  //
+MyFill(T& rng, absl::Span<V> data) {  // NOLINT(runtime/references)
+  rng.Fill(data);
+}
+
+template <typename EngineType>
+class PoolURBGTypedTest : public ::testing::Test {};
+
+using EngineTypes = ::testing::Types<  //
+    RandenPool<uint8_t>,               //
+    RandenPool<uint16_t>,              //
+    RandenPool<uint32_t>,              //
+    RandenPool<uint64_t>,              //
+    PoolURBG<uint8_t, 2>,              //
+    PoolURBG<uint16_t, 2>,             //
+    PoolURBG<uint32_t, 2>,             //
+    PoolURBG<uint64_t, 2>,             //
+    PoolURBG<unsigned int, 8>,         // NOLINT(runtime/int)
+    PoolURBG<unsigned long, 8>,        // NOLINT(runtime/int)
+    PoolURBG<unsigned long int, 4>,    // NOLINT(runtime/int)
+    PoolURBG<unsigned long long, 4>>;  // NOLINT(runtime/int)
+
+TYPED_TEST_SUITE(PoolURBGTypedTest, EngineTypes);
+
+// This test is checks that the engines meet the URBG interface requirements
+// defined in [rand.req.urbg].
+TYPED_TEST(PoolURBGTypedTest, URBGInterface) {
+  using E = TypeParam;
+  using T = typename E::result_type;
+
+  static_assert(std::is_copy_constructible<E>::value,
+                "engine must be copy constructible");
+
+  static_assert(absl::is_copy_assignable<E>::value,
+                "engine must be copy assignable");
+
+  E e;
+  const E x;
+
+  e();
+
+  static_assert(std::is_same<decltype(e()), T>::value,
+                "return type of operator() must be result_type");
+
+  E u0(x);
+  u0();
+
+  E u1 = e;
+  u1();
+}
+
+// This validates that sequences are independent.
+TYPED_TEST(PoolURBGTypedTest, VerifySequences) {
+  using E = TypeParam;
+  using result_type = typename E::result_type;
+
+  E rng;
+  (void)rng();  // Discard one value.
+
+  constexpr int kNumOutputs = 64;
+  result_type a[kNumOutputs];
+  result_type b[kNumOutputs];
+  std::fill(std::begin(b), std::end(b), 0);
+
+  // Fill a using Fill or generate, depending on the engine type.
+  {
+    E x = rng;
+    MyFill(x, absl::MakeSpan(a));
+  }
+
+  // Fill b using std::generate().
+  {
+    E x = rng;
+    std::generate(std::begin(b), std::end(b), x);
+  }
+
+  // Test that generated sequence changed as sequence of bits, i.e. if about
+  // half of the bites were flipped between two non-correlated values.
+  size_t changed_bits = 0;
+  size_t unchanged_bits = 0;
+  size_t total_set = 0;
+  size_t total_bits = 0;
+  size_t equal_count = 0;
+  for (size_t i = 0; i < kNumOutputs; ++i) {
+    equal_count += (a[i] == b[i]) ? 1 : 0;
+    std::bitset<sizeof(result_type) * 8> bitset(a[i] ^ b[i]);
+    changed_bits += bitset.count();
+    unchanged_bits += bitset.size() - bitset.count();
+
+    std::bitset<sizeof(result_type) * 8> a_set(a[i]);
+    std::bitset<sizeof(result_type) * 8> b_set(b[i]);
+    total_set += a_set.count() + b_set.count();
+    total_bits += 2 * 8 * sizeof(result_type);
+  }
+  // On average, half the bits are changed between two calls.
+  EXPECT_LE(changed_bits, 0.60 * (changed_bits + unchanged_bits));
+  EXPECT_GE(changed_bits, 0.40 * (changed_bits + unchanged_bits));
+
+  // verify using a quick normal-approximation to the binomial.
+  EXPECT_NEAR(total_set, total_bits * 0.5, 4 * std::sqrt(total_bits))
+      << "@" << total_set / static_cast<double>(total_bits);
+
+  // Also, A[i] == B[i] with probability (1/range) * N.
+  // Give this a pretty wide latitude, though.
+  const double kExpected = kNumOutputs / (1.0 * sizeof(result_type) * 8);
+  EXPECT_LE(equal_count, 1.0 + kExpected);
+}
+
+}  // namespace
+
+/*
+$ nanobenchmarks 1 RandenPool construct
+$ nanobenchmarks 1 PoolURBG construct
+
+RandenPool<uint32_t> | 1    | 1000 |    48482.00 ticks | 48.48 ticks | 13.9 ns
+RandenPool<uint32_t> | 10   | 2000 |  1028795.00 ticks | 51.44 ticks | 14.7 ns
+RandenPool<uint32_t> | 100  | 1000 |  5119968.00 ticks | 51.20 ticks | 14.6 ns
+RandenPool<uint32_t> | 1000 |  500 | 25867936.00 ticks | 51.74 ticks | 14.8 ns
+
+RandenPool<uint64_t> | 1    | 1000 |    49921.00 ticks | 49.92 ticks | 14.3 ns
+RandenPool<uint64_t> | 10   | 2000 |  1208269.00 ticks | 60.41 ticks | 17.3 ns
+RandenPool<uint64_t> | 100  | 1000 |  5844955.00 ticks | 58.45 ticks | 16.7 ns
+RandenPool<uint64_t> | 1000 |  500 | 28767404.00 ticks | 57.53 ticks | 16.4 ns
+
+PoolURBG<uint32_t,8> | 1    | 1000 |    86431.00 ticks | 86.43 ticks | 24.7 ns
+PoolURBG<uint32_t,8> | 10   | 1000 |   206191.00 ticks | 20.62 ticks |  5.9 ns
+PoolURBG<uint32_t,8> | 100  | 1000 |  1516049.00 ticks | 15.16 ticks |  4.3 ns
+PoolURBG<uint32_t,8> | 1000 |  500 |  7613936.00 ticks | 15.23 ticks |  4.4 ns
+
+PoolURBG<uint64_t,4> | 1    | 1000 |    96668.00 ticks | 96.67 ticks | 27.6 ns
+PoolURBG<uint64_t,4> | 10   | 1000 |   282423.00 ticks | 28.24 ticks |  8.1 ns
+PoolURBG<uint64_t,4> | 100  | 1000 |  2609587.00 ticks | 26.10 ticks |  7.5 ns
+PoolURBG<uint64_t,4> | 1000 |  500 | 12408757.00 ticks | 24.82 ticks |  7.1 ns
+
+*/