mirror of https://gitee.com/bigwinds/arangodb
80 lines
2.1 KiB
C++
80 lines
2.1 KiB
C++
////////////////////////////////////////////////////////////////////////////////
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/// DISCLAIMER
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///
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/// Copyright 2014-2017 ArangoDB GmbH, Cologne, Germany
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/// Copyright 2004-2014 triAGENS GmbH, Cologne, Germany
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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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/// http://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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///
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/// Copyright holder is ArangoDB GmbH, Cologne, Germany
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///
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/// @author Daniel H. Larkin
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////////////////////////////////////////////////////////////////////////////////
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#ifndef ARANGO_SHARED_PRNG_H
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#define ARANGO_SHARED_PRNG_H 1
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#include <memory>
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#include "Basics/Thread.h"
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#include "Basics/fasthash.h"
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#include "Basics/xoroshiro128plus.h"
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namespace arangodb {
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namespace basics {
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struct PaddedPRNG {
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PaddedPRNG();
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void seed(uint64_t seed1, uint64_t seed2);
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inline uint64_t next() { return _prng.next(); }
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private:
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#if defined(__clang__)
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#pragma clang diagnostic push
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#pragma clang diagnostic ignored "-Wunused-private-field"
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#endif
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// this padding is intentionally here
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uint8_t frontPadding[64];
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xoroshiro128plus _prng;
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uint8_t backpadding[64 - sizeof(xoroshiro128plus)];
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#if defined(__clang__)
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#pragma clang diagnostic pop
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#endif
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};
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struct SharedPRNG {
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static inline uint64_t rand() { return _global->next(); }
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SharedPRNG();
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private:
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// never want two live threads to hash to the same stripe
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static constexpr uint64_t _stripes = (1 << 16);
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static std::unique_ptr<SharedPRNG> _global;
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PaddedPRNG _prng[_stripes];
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uint64_t _mask;
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inline uint64_t id() {
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return fasthash64_uint64(Thread::currentThreadNumber(), 0xdeadbeefdeadbeefULL);
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}
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inline uint64_t next() { return _prng[id() & _mask].next(); }
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};
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} // namespace basics
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} // namespace arangodb
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#endif
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