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delete the random number generator
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Nicole Mazzuca
parent
2d6df16849
commit
43493b56df
@ -1,199 +0,0 @@
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#pragma once
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#include <cstdint>
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#include <limits>
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#include <random>
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namespace vcpkg::Rng {
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namespace detail {
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template <class T>
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constexpr std::size_t bitsize = sizeof(T) * CHAR_BITS;
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template <class T>
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constexpr bool is_valid_shift(int k) {
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return 0 <= k && k <= bitsize<T>;
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}
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// precondition: 0 <= k < bitsize<T>
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template <class T>
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constexpr T ror(T x, int k) {
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if (k == 0) {
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return x;
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}
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return (x >> k) | (x << (bitsize<T> - k));
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}
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// precondition: 0 <= k < bitsize<T>
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template <class T>
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constexpr T rol(T x, int k) {
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if (k == 0) {
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return x;
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}
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return (x << k) | (x >> (bitsize<T> - k));
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}
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// there _is_ a way to do this generally, but I don't know how to
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template <class UIntType, int e>
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struct XoshiroJumpTable;
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template <>
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struct XoshiroJumpTable<std::uint64_t, 128> {
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constexpr static std::uint64_t value[4] = {
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0x180ec6d33cfd0aba, 0xd5a61266f0c9392c, 0xa9582618e03fc9aa, 0x39abdc4529b1661c
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};
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};
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}
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/*
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NOTE(ubsan): taken from the xoshiro paper
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initialized from random_device by default
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actual code is copied from wikipedia, since I wrote that code
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*/
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struct splitmix {
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splitmix() noexcept;
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constexpr splitmix(std::uint64_t seed) noexcept
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: state(seed) {}
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constexpr std::uint64_t operator()() noexcept {
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state += 0x9E3779B97F4A7C15;
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std::uint64_t result = state;
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result = (result ^ (result >> 30)) * 0xBF58476D1CE4E5B9;
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result = (result ^ (result >> 27)) * 0x94D049BB133111EB;
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return result ^ (result >> 31);
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}
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constexpr std::uint64_t max() const noexcept {
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return std::numeric_limits<std::uint64_t>::max();
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}
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constexpr std::uint64_t min() const noexcept {
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return std::numeric_limits<std::uint64_t>::min();
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}
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template <class T>
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constexpr void fill(T* first, T* last) {
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constexpr auto mask =
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static_cast<std::uint64_t>(std::numeric_limits<T>::max());
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const auto remaining =
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(last - first) % (sizeof(std::uint64_t) / sizeof(T));
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for (auto it = first; it != last - remaining;) {
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const auto item = (*this)();
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for (
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int shift = 0;
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shift < 64;
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shift += detail::bitsize<T>, ++it
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) {
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*it = static_cast<T>((item >> shift) & mask);
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}
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}
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if (remaining == 0) return;
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int shift = 0;
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const auto item = (*this)();
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for (auto it = last - remaining;
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it != last;
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shift += detail::bitsize<T>, ++it
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) {
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*it = static_cast<T>((item >> shift) & mask);
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}
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}
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private:
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std::uint64_t state;
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};
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template <class UIntType, int S, int R, int T>
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struct starstar_scrambler {
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constexpr static UIntType scramble(UIntType n) noexcept {
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return detail::rol(n * S, R) * T;
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}
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};
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// Sebastian Vigna's xorshift-based xoshiro engine
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// fast and really good
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// uses the splitmix to initialize state
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template <class UIntType, class Scrambler, int A, int B>
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struct xoshiro_engine {
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static_assert(detail::is_valid_shift<UIntType>(A));
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static_assert(detail::is_valid_shift<UIntType>(B));
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static_assert(std::is_unsigned_v<UIntType>);
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// splitmix will be initialized with random_device
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xoshiro_engine() noexcept {
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splitmix sm{};
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sm.fill(&state[0], &state[4]);
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}
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constexpr xoshiro_engine(std::uint64_t seed) noexcept : state() {
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splitmix sm{seed};
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sm.fill(&state[0], &state[4]);
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}
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constexpr UIntType operator()() noexcept {
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const UIntType result = Scrambler::scramble(state[0]);
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const UIntType t = state[1] << A;
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state[2] ^= state[0];
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state[3] ^= state[1];
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state[1] ^= state[2];
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state[0] ^= state[3];
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state[2] ^= t;
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state[3] ^= detail::rol(state[3], B);
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return result;
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}
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constexpr UIntType max() const noexcept {
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return std::numeric_limits<UIntType>::max();
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}
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constexpr std::uint64_t min() const noexcept {
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return std::numeric_limits<UIntType>::min();
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}
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// quickly jump ahead 2^e steps
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// takes 4 * bitsize<UIntType> rng next operations
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template <int e>
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constexpr void discard_e() noexcept {
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using JT = detail::XoshiroJumpTable<UIntType, e>;
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UIntType s[4] = {};
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for (const auto& jump : JT::value) {
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for (std::size_t i = 0; i < bitsize<UIntType>; ++i) {
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if ((jump >> i) & 1) {
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s[0] ^= state[0];
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s[1] ^= state[1];
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s[2] ^= state[2];
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s[3] ^= state[3];
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}
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(*this)();
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}
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}
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state[0] = s[0];
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state[1] = s[1];
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state[2] = s[2];
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state[3] = s[3];
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}
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private:
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// rotate left
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UIntType state[4];
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};
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using xoshiro256ss = xoshiro_engine<
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std::uint64_t,
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starstar_scrambler<std::uint64_t, 5, 7, 9>,
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17,
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45>;
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}
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@ -1,14 +0,0 @@
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#include <base/rng.h>
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namespace vcpkg::Rng {
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namespace {
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std::random_device system_entropy{};
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}
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splitmix::splitmix() {
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std::uint64_t top_half = system_entropy();
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std::uint64_t bottom_half = system_entropy();
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state = (top_half << 32) | bottom_half;
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}
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}
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