132 lines
4.0 KiB
C++
132 lines
4.0 KiB
C++
// 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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#ifndef ABSL_RANDOM_INTERNAL_POOL_URBG_H_
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#define ABSL_RANDOM_INTERNAL_POOL_URBG_H_
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#include <cinttypes>
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#include <limits>
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#include "absl/random/internal/traits.h"
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#include "absl/types/span.h"
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namespace absl {
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ABSL_NAMESPACE_BEGIN
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namespace random_internal {
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// RandenPool is a thread-safe random number generator [random.req.urbg] that
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// uses an underlying pool of Randen generators to generate values. Each thread
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// has affinity to one instance of the underlying pool generators. Concurrent
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// access is guarded by a spin-lock.
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template <typename T>
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class RandenPool {
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public:
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using result_type = T;
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static_assert(std::is_unsigned<result_type>::value,
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"RandenPool template argument must be a built-in unsigned "
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"integer type");
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static constexpr result_type(min)() {
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return (std::numeric_limits<result_type>::min)();
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}
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static constexpr result_type(max)() {
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return (std::numeric_limits<result_type>::max)();
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}
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RandenPool() {}
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// Returns a single value.
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inline result_type operator()() { return Generate(); }
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// Fill data with random values.
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static void Fill(absl::Span<result_type> data);
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protected:
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// Generate returns a single value.
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static result_type Generate();
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};
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extern template class RandenPool<uint8_t>;
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extern template class RandenPool<uint16_t>;
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extern template class RandenPool<uint32_t>;
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extern template class RandenPool<uint64_t>;
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// PoolURBG uses an underlying pool of random generators to implement a
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// thread-compatible [random.req.urbg] interface with an internal cache of
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// values.
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template <typename T, size_t kBufferSize>
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class PoolURBG {
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// Inheritance to access the protected static members of RandenPool.
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using unsigned_type = typename make_unsigned_bits<T>::type;
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using PoolType = RandenPool<unsigned_type>;
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using SpanType = absl::Span<unsigned_type>;
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static constexpr size_t kInitialBuffer = kBufferSize + 1;
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static constexpr size_t kHalfBuffer = kBufferSize / 2;
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public:
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using result_type = T;
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static_assert(std::is_unsigned<result_type>::value,
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"PoolURBG must be parameterized by an unsigned integer type");
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static_assert(kBufferSize > 1,
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"PoolURBG must be parameterized by a buffer-size > 1");
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static_assert(kBufferSize <= 256,
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"PoolURBG must be parameterized by a buffer-size <= 256");
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static constexpr result_type(min)() {
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return (std::numeric_limits<result_type>::min)();
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}
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static constexpr result_type(max)() {
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return (std::numeric_limits<result_type>::max)();
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}
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PoolURBG() : next_(kInitialBuffer) {}
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// copy-constructor does not copy cache.
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PoolURBG(const PoolURBG&) : next_(kInitialBuffer) {}
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const PoolURBG& operator=(const PoolURBG&) {
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next_ = kInitialBuffer;
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return *this;
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}
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// move-constructor does move cache.
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PoolURBG(PoolURBG&&) = default;
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PoolURBG& operator=(PoolURBG&&) = default;
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inline result_type operator()() {
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if (next_ >= kBufferSize) {
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next_ = (kBufferSize > 2 && next_ > kBufferSize) ? kHalfBuffer : 0;
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PoolType::Fill(SpanType(reinterpret_cast<unsigned_type*>(state_ + next_),
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kBufferSize - next_));
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}
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return state_[next_++];
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}
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private:
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// Buffer size.
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size_t next_; // index within state_
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result_type state_[kBufferSize];
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};
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} // namespace random_internal
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ABSL_NAMESPACE_END
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} // namespace absl
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#endif // ABSL_RANDOM_INTERNAL_POOL_URBG_H_
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