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// random.h
/**
* Copyright (C) 2018-present MongoDB, Inc.
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the Server Side Public License, version 1,
* as published by MongoDB, Inc.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* Server Side Public License for more details.
*
* You should have received a copy of the Server Side Public License
* along with this program. If not, see
* <http://www.mongodb.com/licensing/server-side-public-license>.
*
* As a special exception, the copyright holders give permission to link the
* code of portions of this program with the OpenSSL library under certain
* conditions as described in each individual source file and distribute
* linked combinations including the program with the OpenSSL library. You
* must comply with the Server Side Public License in all respects for
* all of the code used other than as permitted herein. If you modify file(s)
* with this exception, you may extend this exception to your version of the
* file(s), but you are not obligated to do so. If you do not wish to do so,
* delete this exception statement from your version. If you delete this
* exception statement from all source files in the program, then also delete
* it in the license file.
*/
#pragma once
#include <cstdint>
#include <limits>
#include <memory>
namespace mongo {
/**
* Uses http://en.wikipedia.org/wiki/Xorshift
*/
class PseudoRandom {
public:
PseudoRandom(int32_t seed);
PseudoRandom(uint32_t seed);
PseudoRandom(int64_t seed);
int32_t nextInt32();
int64_t nextInt64();
/**
* Returns a random number in the range [0, 1).
*/
double nextCanonicalDouble();
/**
* @return a number between 0 and max
*/
int32_t nextInt32(int32_t max) {
return static_cast<uint32_t>(nextInt32()) % static_cast<uint32_t>(max);
}
/**
* @return a number between 0 and max
*/
int64_t nextInt64(int64_t max) {
return static_cast<uint64_t>(nextInt64()) % static_cast<uint64_t>(max);
}
/**
* This returns an object that adapts PseudoRandom such that it
* can be used as the third argument to std::shuffle. Note that
* the lifetime of the returned object must be a subset of the
* lifetime of the PseudoRandom object.
*/
auto urbg() {
class URBG {
public:
explicit URBG(PseudoRandom* impl) : _impl(impl) {}
using result_type = uint64_t;
static constexpr result_type min() {
return std::numeric_limits<result_type>::min();
}
static constexpr result_type max() {
return std::numeric_limits<result_type>::max();
}
result_type operator()() {
return _impl->nextInt64();
}
private:
PseudoRandom* _impl;
};
return URBG(this);
}
private:
uint32_t nextUInt32();
uint32_t _x;
uint32_t _y;
uint32_t _z;
uint32_t _w;
};
/**
* More secure random numbers
* Suitable for nonce/crypto
* Slower than PseudoRandom, so only use when really need
*/
class SecureRandom {
public:
virtual ~SecureRandom();
virtual int64_t nextInt64() = 0;
static std::unique_ptr<SecureRandom> create();
};
} // namespace mongo
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