254 lines
7.9 KiB
C++
254 lines
7.9 KiB
C++
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// Copyright 2017 The Abseil Authors.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// https://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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#include "absl/random/internal/pool_urbg.h"
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#include <algorithm>
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#include <atomic>
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#include <cstdint>
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#include <cstring>
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#include <iterator>
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#include "absl/base/attributes.h"
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#include "absl/base/call_once.h"
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#include "absl/base/config.h"
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#include "absl/base/internal/endian.h"
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#include "absl/base/internal/raw_logging.h"
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#include "absl/base/internal/spinlock.h"
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#include "absl/base/internal/sysinfo.h"
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#include "absl/base/internal/unaligned_access.h"
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#include "absl/base/optimization.h"
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#include "absl/random/internal/randen.h"
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#include "absl/random/internal/seed_material.h"
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#include "absl/random/seed_gen_exception.h"
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using absl::base_internal::SpinLock;
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using absl::base_internal::SpinLockHolder;
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namespace absl {
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ABSL_NAMESPACE_BEGIN
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namespace random_internal {
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namespace {
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// RandenPoolEntry is a thread-safe pseudorandom bit generator, implementing a
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// single generator within a RandenPool<T>. It is an internal implementation
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// detail, and does not aim to conform to [rand.req.urng].
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//
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// NOTE: There are alignment issues when used on ARM, for instance.
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// See the allocation code in PoolAlignedAlloc().
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class RandenPoolEntry {
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public:
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static constexpr size_t kState = RandenTraits::kStateBytes / sizeof(uint32_t);
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static constexpr size_t kCapacity =
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RandenTraits::kCapacityBytes / sizeof(uint32_t);
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void Init(absl::Span<const uint32_t> data) {
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SpinLockHolder l(&mu_); // Always uncontested.
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std::copy(data.begin(), data.end(), std::begin(state_));
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next_ = kState;
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}
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// Copy bytes into out.
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void Fill(uint8_t* out, size_t bytes) ABSL_LOCKS_EXCLUDED(mu_);
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// Returns random bits from the buffer in units of T.
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template <typename T>
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inline T Generate() ABSL_LOCKS_EXCLUDED(mu_);
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inline void MaybeRefill() ABSL_EXCLUSIVE_LOCKS_REQUIRED(mu_) {
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if (next_ >= kState) {
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next_ = kCapacity;
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impl_.Generate(state_);
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}
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}
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private:
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// Randen URBG state.
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uint32_t state_[kState] ABSL_GUARDED_BY(mu_); // First to satisfy alignment.
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SpinLock mu_;
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const Randen impl_;
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size_t next_ ABSL_GUARDED_BY(mu_);
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};
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template <>
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inline uint8_t RandenPoolEntry::Generate<uint8_t>() {
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SpinLockHolder l(&mu_);
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MaybeRefill();
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return static_cast<uint8_t>(state_[next_++]);
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}
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template <>
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inline uint16_t RandenPoolEntry::Generate<uint16_t>() {
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SpinLockHolder l(&mu_);
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MaybeRefill();
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return static_cast<uint16_t>(state_[next_++]);
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}
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template <>
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inline uint32_t RandenPoolEntry::Generate<uint32_t>() {
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SpinLockHolder l(&mu_);
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MaybeRefill();
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return state_[next_++];
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}
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template <>
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inline uint64_t RandenPoolEntry::Generate<uint64_t>() {
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SpinLockHolder l(&mu_);
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if (next_ >= kState - 1) {
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next_ = kCapacity;
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impl_.Generate(state_);
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}
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auto p = state_ + next_;
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next_ += 2;
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uint64_t result;
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std::memcpy(&result, p, sizeof(result));
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return result;
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}
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void RandenPoolEntry::Fill(uint8_t* out, size_t bytes) {
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SpinLockHolder l(&mu_);
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while (bytes > 0) {
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MaybeRefill();
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size_t remaining = (kState - next_) * sizeof(state_[0]);
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size_t to_copy = std::min(bytes, remaining);
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std::memcpy(out, &state_[next_], to_copy);
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out += to_copy;
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bytes -= to_copy;
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next_ += (to_copy + sizeof(state_[0]) - 1) / sizeof(state_[0]);
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}
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}
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// Number of pooled urbg entries.
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static constexpr int kPoolSize = 8;
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// Shared pool entries.
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static absl::once_flag pool_once;
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ABSL_CACHELINE_ALIGNED static RandenPoolEntry* shared_pools[kPoolSize];
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// Returns an id in the range [0 ... kPoolSize), which indexes into the
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// pool of random engines.
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//
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// Each thread to access the pool is assigned a sequential ID (without reuse)
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// from the pool-id space; the id is cached in a thread_local variable.
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// This id is assigned based on the arrival-order of the thread to the
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// GetPoolID call; this has no binary, CL, or runtime stability because
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// on subsequent runs the order within the same program may be significantly
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// different. However, as other thread IDs are not assigned sequentially,
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// this is not expected to matter.
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int GetPoolID() {
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static_assert(kPoolSize >= 1,
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"At least one urbg instance is required for PoolURBG");
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ABSL_CONST_INIT static std::atomic<int64_t> sequence{0};
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#ifdef ABSL_HAVE_THREAD_LOCAL
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static thread_local int my_pool_id = -1;
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if (ABSL_PREDICT_FALSE(my_pool_id < 0)) {
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my_pool_id = (sequence++ % kPoolSize);
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}
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return my_pool_id;
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#else
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static pthread_key_t tid_key = [] {
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pthread_key_t tmp_key;
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int err = pthread_key_create(&tmp_key, nullptr);
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if (err) {
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ABSL_RAW_LOG(FATAL, "pthread_key_create failed with %d", err);
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}
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return tmp_key;
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}();
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// Store the value in the pthread_{get/set}specific. However an uninitialized
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// value is 0, so add +1 to distinguish from the null value.
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intptr_t my_pool_id =
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reinterpret_cast<intptr_t>(pthread_getspecific(tid_key));
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if (ABSL_PREDICT_FALSE(my_pool_id == 0)) {
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// No allocated ID, allocate the next value, cache it, and return.
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my_pool_id = (sequence++ % kPoolSize) + 1;
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int err = pthread_setspecific(tid_key, reinterpret_cast<void*>(my_pool_id));
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if (err) {
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ABSL_RAW_LOG(FATAL, "pthread_setspecific failed with %d", err);
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}
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}
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return my_pool_id - 1;
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#endif
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}
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// Allocate a RandenPoolEntry with at least 32-byte alignment, which is required
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// by ARM platform code.
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RandenPoolEntry* PoolAlignedAlloc() {
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constexpr size_t kAlignment =
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ABSL_CACHELINE_SIZE > 32 ? ABSL_CACHELINE_SIZE : 32;
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// Not all the platforms that we build for have std::aligned_alloc, however
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// since we never free these objects, we can over allocate and munge the
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// pointers to the correct alignment.
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intptr_t x = reinterpret_cast<intptr_t>(
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new char[sizeof(RandenPoolEntry) + kAlignment]);
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auto y = x % kAlignment;
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void* aligned = reinterpret_cast<void*>(y == 0 ? x : (x + kAlignment - y));
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return new (aligned) RandenPoolEntry();
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}
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// Allocate and initialize kPoolSize objects of type RandenPoolEntry.
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//
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// The initialization strategy is to initialize one object directly from
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// OS entropy, then to use that object to seed all of the individual
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// pool instances.
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void InitPoolURBG() {
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static constexpr size_t kSeedSize =
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RandenTraits::kStateBytes / sizeof(uint32_t);
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// Read the seed data from OS entropy once.
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uint32_t seed_material[kPoolSize * kSeedSize];
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if (!random_internal::ReadSeedMaterialFromOSEntropy(
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absl::MakeSpan(seed_material))) {
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random_internal::ThrowSeedGenException();
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}
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for (int i = 0; i < kPoolSize; i++) {
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shared_pools[i] = PoolAlignedAlloc();
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shared_pools[i]->Init(
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absl::MakeSpan(&seed_material[i * kSeedSize], kSeedSize));
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}
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}
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// Returns the pool entry for the current thread.
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RandenPoolEntry* GetPoolForCurrentThread() {
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absl::call_once(pool_once, InitPoolURBG);
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return shared_pools[GetPoolID()];
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}
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} // namespace
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template <typename T>
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typename RandenPool<T>::result_type RandenPool<T>::Generate() {
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auto* pool = GetPoolForCurrentThread();
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return pool->Generate<T>();
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}
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template <typename T>
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void RandenPool<T>::Fill(absl::Span<result_type> data) {
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auto* pool = GetPoolForCurrentThread();
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pool->Fill(reinterpret_cast<uint8_t*>(data.data()),
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data.size() * sizeof(result_type));
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}
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template class RandenPool<uint8_t>;
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template class RandenPool<uint16_t>;
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template class RandenPool<uint32_t>;
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template class RandenPool<uint64_t>;
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} // namespace random_internal
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ABSL_NAMESPACE_END
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} // namespace absl
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