// 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
*/
