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/* SPDX-License-Identifier: BSL-1.0 OR BSD-3-Clause */
#ifndef MPT_RANDOM_DEVICE_HPP
#define MPT_RANDOM_DEVICE_HPP
#include "mpt/base/bit.hpp"
#include "mpt/base/detect.hpp"
#include "mpt/base/macros.hpp"
#include "mpt/base/math.hpp"
#include "mpt/base/integer.hpp"
#include "mpt/base/namespace.hpp"
#include "mpt/crc/crc.hpp"
#include "mpt/endian/integer.hpp"
#include "mpt/mutex/mutex.hpp"
#include "mpt/out_of_memory/out_of_memory.hpp"
#include "mpt/random/engine.hpp"
#include "mpt/random/engine_lcg.hpp"
#include "mpt/random/random.hpp"
#include <chrono>
#include <limits>
#include <memory>
#include <random>
#include <string>
#include <cmath>
#include <cstring>
namespace mpt {
inline namespace MPT_INLINE_NS {
inline constexpr uint32 DETERMINISTIC_RNG_SEED = 3141592653u; // pi
template <typename T>
struct default_radom_seed_hash {
};
template <>
struct default_radom_seed_hash<uint8> {
using type = mpt::crc16;
};
template <>
struct default_radom_seed_hash<uint16> {
using type = mpt::crc16;
};
template <>
struct default_radom_seed_hash<uint32> {
using type = mpt::crc32c;
};
template <>
struct default_radom_seed_hash<uint64> {
using type = mpt::crc64_jones;
};
class prng_random_device_time_seeder {
public:
template <typename T>
inline T generate_seed() {
// Note: CRC is actually not that good a choice here, but it is simple and we
// already have an implementaion available. Better choices for mixing entropy
// would be a hash function with proper avalanche characteristics or a block
// or stream cipher with any pre-choosen random key and IV. The only aspect we
// really need here is whitening of the bits.
typename mpt::default_radom_seed_hash<T>::type hash;
{
uint64be time;
time = std::chrono::duration_cast<std::chrono::nanoseconds>(std::chrono::system_clock().now().time_since_epoch()).count();
std::byte bytes[sizeof(time)];
std::memcpy(bytes, &time, sizeof(time));
hash(std::begin(bytes), std::end(bytes));
}
#if !defined(MPT_COMPILER_QUIRK_CHRONO_NO_HIGH_RESOLUTION_CLOCK)
// Avoid std::chrono::high_resolution_clock on Emscripten because availability is problematic in AudioWorklet context.
{
uint64be time;
time = std::chrono::duration_cast<std::chrono::nanoseconds>(std::chrono::high_resolution_clock().now().time_since_epoch()).count();
std::byte bytes[sizeof(time)];
std::memcpy(bytes, &time, sizeof(time));
hash(std::begin(bytes), std::end(bytes));
}
#endif // !MPT_COMPILER_QUIRK_CHRONO_NO_HIGH_RESOLUTION_CLOCK
return static_cast<T>(hash.result());
}
public:
prng_random_device_time_seeder() = default;
};
// C++11 std::random_device may be implemented as a deterministic PRNG.
// There is no way to seed this PRNG and it is allowed to be seeded with the
// same value on each program invocation. This makes std::random_device
// completely useless even as a non-cryptographic entropy pool.
// We fallback to time-seeded std::mt19937 if std::random_device::entropy() is
// 0 or less.
class sane_random_device {
private:
mpt::mutex m;
std::string token;
#if !defined(MPT_COMPILER_QUIRK_RANDOM_NO_RANDOM_DEVICE)
std::unique_ptr<std::random_device> prd;
bool rd_reliable{false};
#endif // !MPT_COMPILER_QUIRK_RANDOM_NO_RANDOM_DEVICE
std::unique_ptr<std::mt19937> rd_fallback;
public:
using result_type = unsigned int;
private:
void init_fallback() {
if (!rd_fallback) {
if (token.length() > 0) {
uint64 seed_val = mpt::prng_random_device_time_seeder().generate_seed<uint64>();
std::vector<unsigned int> seeds;
seeds.push_back(static_cast<uint32>(seed_val >> 32));
seeds.push_back(static_cast<uint32>(seed_val >> 0));
for (std::size_t i = 0; i < token.length(); ++i) {
seeds.push_back(static_cast<unsigned int>(static_cast<unsigned char>(token[i])));
}
std::seed_seq seed(seeds.begin(), seeds.end());
rd_fallback = std::make_unique<std::mt19937>(seed);
} else {
uint64 seed_val = mpt::prng_random_device_time_seeder().generate_seed<uint64>();
unsigned int seeds[2];
seeds[0] = static_cast<uint32>(seed_val >> 32);
seeds[1] = static_cast<uint32>(seed_val >> 0);
std::seed_seq seed(seeds + 0, seeds + 2);
rd_fallback = std::make_unique<std::mt19937>(seed);
}
}
}
public:
sane_random_device() {
#if !defined(MPT_COMPILER_QUIRK_RANDOM_NO_RANDOM_DEVICE)
try {
prd = std::make_unique<std::random_device>();
rd_reliable = ((*prd).entropy() > 0.0);
} catch (mpt::out_of_memory e) {
mpt::rethrow_out_of_memory(e);
} catch (const std::exception &) {
rd_reliable = false;
}
if (!rd_reliable) {
init_fallback();
}
#else // MPT_COMPILER_QUIRK_RANDOM_NO_RANDOM_DEVICE
init_fallback();
#endif // !MPT_COMPILER_QUIRK_RANDOM_NO_RANDOM_DEVICE
}
sane_random_device(const std::string & token_)
: token(token_) {
#if !defined(MPT_COMPILER_QUIRK_RANDOM_NO_RANDOM_DEVICE)
try {
prd = std::make_unique<std::random_device>(token);
rd_reliable = ((*prd).entropy() > 0.0);
} catch (mpt::out_of_memory e) {
mpt::rethrow_out_of_memory(e);
} catch (const std::exception &) {
rd_reliable = false;
}
if (!rd_reliable) {
init_fallback();
}
#else // MPT_COMPILER_QUIRK_RANDOM_NO_RANDOM_DEVICE
init_fallback();
#endif // !MPT_COMPILER_QUIRK_RANDOM_NO_RANDOM_DEVICE
}
static MPT_CONSTEXPRINLINE result_type min() {
return std::numeric_limits<result_type>::min();
}
static MPT_CONSTEXPRINLINE result_type max() {
return std::numeric_limits<result_type>::max();
}
static MPT_CONSTEXPRINLINE int result_bits() {
return sizeof(result_type) * 8;
}
result_type operator()() {
mpt::lock_guard<mpt::mutex> l(m);
result_type result = 0;
#if !defined(MPT_COMPILER_QUIRK_RANDOM_NO_RANDOM_DEVICE)
if (prd) {
try {
if constexpr (std::random_device::min() != 0 || !mpt::is_mask(std::random_device::max())) {
// insane std::random_device
// This implementation is not exactly uniformly distributed but good enough
// for OpenMPT.
constexpr double rd_min = static_cast<double>(std::random_device::min());
constexpr double rd_max = static_cast<double>(std::random_device::max());
constexpr double rd_range = rd_max - rd_min;
constexpr double rd_size = rd_range + 1.0;
const double rd_entropy = mpt::log2(rd_size);
const int iterations = static_cast<int>(std::ceil(result_bits() / rd_entropy));
double tmp = 0.0;
for (int i = 0; i < iterations; ++i) {
tmp = (tmp * rd_size) + (static_cast<double>((*prd)()) - rd_min);
}
double result_01 = std::floor(tmp / std::pow(rd_size, iterations));
result = static_cast<result_type>(std::floor(result_01 * (static_cast<double>(max() - min()) + 1.0))) + min();
} else {
// sane std::random_device
result = 0;
std::size_t rd_bits = mpt::lower_bound_entropy_bits(std::random_device::max());
for (std::size_t entropy = 0; entropy < (sizeof(result_type) * 8); entropy += rd_bits) {
if (rd_bits < (sizeof(result_type) * 8)) {
result = (result << rd_bits) | static_cast<result_type>((*prd)());
} else {
result = result | static_cast<result_type>((*prd)());
}
}
}
} catch (const std::exception &) {
rd_reliable = false;
init_fallback();
}
} else {
rd_reliable = false;
}
if (!rd_reliable) {
// std::random_device is unreliable
// XOR the generated random number with more entropy from the time-seeded
// PRNG.
// Note: This is safe even if the std::random_device itself is implemented
// as a std::mt19937 PRNG because we are very likely using a different
// seed.
result ^= mpt::random<result_type>(*rd_fallback);
}
#else // MPT_COMPILER_QUIRK_RANDOM_NO_RANDOM_DEVICE
result ^= mpt::random<result_type>(*rd_fallback);
#endif // !MPT_COMPILER_QUIRK_RANDOM_NO_RANDOM_DEVICE
return result;
}
};
class prng_random_device_deterministic_seeder {
protected:
template <typename T>
constexpr T generate_seed() noexcept {
return static_cast<T>(mpt::DETERMINISTIC_RNG_SEED);
}
protected:
prng_random_device_deterministic_seeder() = default;
};
template <typename Trng = mpt::lcg_musl, typename seeder = mpt::prng_random_device_time_seeder>
class prng_random_device
: private seeder {
public:
using result_type = unsigned int;
private:
mpt::mutex m;
Trng rng;
public:
prng_random_device()
: rng(seeder::template generate_seed<typename Trng::state_type>()) {
return;
}
prng_random_device(const std::string &)
: rng(seeder::template generate_seed<typename Trng::state_type>()) {
return;
}
static MPT_CONSTEXPRINLINE result_type min() {
return std::numeric_limits<unsigned int>::min();
}
static MPT_CONSTEXPRINLINE result_type max() {
return std::numeric_limits<unsigned int>::max();
}
static MPT_CONSTEXPRINLINE int result_bits() {
return sizeof(unsigned int) * 8;
}
result_type operator()() {
mpt::lock_guard<mpt::mutex> l(m);
return mpt::random<unsigned int>(rng);
}
};
using deterministc_random_device = mpt::prng_random_device<mpt::lcg_musl, mpt::prng_random_device_deterministic_seeder>;
} // namespace MPT_INLINE_NS
} // namespace mpt
#endif // MPT_RANDOM_DEVICE_HPP
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