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/**
* 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 <algorithm>
#include <cstdint>
#include <cstring>
#include <limits>
#include <memory>
#include <random>
namespace mongo {
/**
* A uniform random bit generator based on XorShift.
* Uses http://en.wikipedia.org/wiki/Xorshift
*/
class XorShift128 {
public:
using result_type = uint32_t;
static constexpr result_type min() {
return std::numeric_limits<result_type>::lowest();
}
static constexpr result_type max() {
return std::numeric_limits<result_type>::max();
}
explicit XorShift128(uint32_t seed) : _x{seed} {}
result_type operator()() {
uint32_t t = _x ^ (_x << 11);
_x = _y;
_y = _z;
_z = _w;
return _w = _w ^ (_w >> 19) ^ (t ^ (t >> 8));
}
private:
uint32_t _x; // seed
uint32_t _y = 362436069;
uint32_t _z = 521288629;
uint32_t _w = 88675123;
};
/** The SecureUrbg impls all produce the full range of uint64_t. */
class SecureUrbg {
public:
using result_type = uint64_t;
static constexpr result_type min() {
return std::numeric_limits<result_type>::lowest();
}
static constexpr result_type max() {
return std::numeric_limits<result_type>::max();
}
// Details including State vary by platform and are deferred to the .cpp file.
SecureUrbg();
~SecureUrbg();
result_type operator()();
private:
class State;
std::unique_ptr<State> _state;
};
// Provides mongo-traditional functions around a pluggable UniformRandomBitGenerator.
template <typename Urbg>
class RandomBase {
public:
using urbg_type = Urbg;
RandomBase() : _urbg{} {}
explicit RandomBase(urbg_type u) : _urbg{std::move(u)} {}
/** The underlying generator */
urbg_type& urbg() {
return _urbg;
}
/** A random number in the range [0, 1). */
double nextCanonicalDouble() {
return std::uniform_real_distribution<double>{0, 1}(_urbg);
}
/** A number uniformly distributed over all possible values. */
int32_t nextInt32() {
return _nextAny<int32_t>();
}
/** A number uniformly distributed over all possible values. */
int64_t nextInt64() {
return _nextAny<int64_t>();
}
/** A number in the half-open interval [0, max) */
int32_t nextInt32(int32_t max) {
return std::uniform_int_distribution<int32_t>(0, max - 1)(_urbg);
}
/** A number in the half-open interval [0, max) */
int64_t nextInt64(int64_t max) {
return std::uniform_int_distribution<int64_t>(0, max - 1)(_urbg);
}
/**
A number uniformly distributed over all possible values that can be safely represented as
double without loosing precision.
*/
int64_t nextInt64SafeDoubleRepresentable() {
const int64_t maxRepresentableLimit =
static_cast<int64_t>(std::ldexp(1, std::numeric_limits<double>::digits)) + 1;
return nextInt64(maxRepresentableLimit);
}
/** Fill array `buf` with `n` random bytes. */
void fill(void* buf, size_t n) {
const auto p = static_cast<uint8_t*>(buf);
size_t written = 0;
while (written < n) {
uint64_t t = nextInt64();
size_t w = std::min(n - written, sizeof(t));
std::memcpy(p + written, &t, w);
written += w;
}
}
private:
template <typename T>
T _nextAny() {
using Limits = std::numeric_limits<T>;
return std::uniform_int_distribution<T>(Limits::lowest(), Limits::max())(_urbg);
}
urbg_type _urbg;
};
/**
* A Pseudorandom generator that's not cryptographically secure, but very fast and small.
*/
class PseudoRandom : public RandomBase<XorShift128> {
using Base = RandomBase<XorShift128>;
public:
explicit PseudoRandom(uint32_t seed) : Base{XorShift128{seed}} {}
explicit PseudoRandom(int32_t seed) : PseudoRandom{static_cast<uint32_t>(seed)} {}
explicit PseudoRandom(uint64_t seed)
: PseudoRandom{static_cast<uint32_t>(seed ^ (seed >> 32))} {}
explicit PseudoRandom(int64_t seed) : PseudoRandom{static_cast<uint64_t>(seed)} {}
};
/**
* More secure random numbers
* Suitable for nonce/crypto
* Slower than PseudoRandom, so only use when really need
*/
class SecureRandom : public RandomBase<SecureUrbg> {
using Base = RandomBase<SecureUrbg>;
public:
using Base::Base;
};
} // namespace mongo
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