--- /dev/null
+// Copyright 2018 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#ifndef ABSL_RANDOM_PCG_ENGINE_H_
+#define ABSL_RANDOM_PCG_ENGINE_H_
+
+#include <type_traits>
+
+#include "absl/base/config.h"
+#include "absl/meta/type_traits.h"
+#include "absl/numeric/int128.h"
+#include "absl/random/internal/fastmath.h"
+#include "absl/random/internal/iostream_state_saver.h"
+
+namespace absl {
+namespace random_internal {
+
+// pcg_engine is a simplified implementation of Melissa O'Neil's PCG engine in
+// C++. PCG combines a linear congruential generator (LCG) with output state
+// mixing functions to generate each random variate. pcg_engine supports only a
+// single sequence (oneseq), and does not support streams.
+//
+// pcg_engine is parameterized by two types:
+// Params, which provides the multiplier and increment values;
+// Mix, which mixes the state into the result.
+//
+template <typename Params, typename Mix>
+class pcg_engine {
+ static_assert(std::is_same<typename Params::state_type,
+ typename Mix::state_type>::value,
+ "Class-template absl::pcg_engine must be parameterized by "
+ "Params and Mix with identical state_type");
+
+ static_assert(std::is_unsigned<typename Mix::result_type>::value,
+ "Class-template absl::pcg_engine must be parameterized by "
+ "an unsigned Mix::result_type");
+
+ using params_type = Params;
+ using mix_type = Mix;
+ using state_type = typename Mix::state_type;
+
+ public:
+ // C++11 URBG interface:
+ using result_type = typename Mix::result_type;
+
+ static constexpr result_type(min)() {
+ return (std::numeric_limits<result_type>::min)();
+ }
+
+ static constexpr result_type(max)() {
+ return (std::numeric_limits<result_type>::max)();
+ }
+
+ explicit pcg_engine(uint64_t seed_value = 0) { seed(seed_value); }
+
+ template <class SeedSequence,
+ typename = typename absl::enable_if_t<
+ !std::is_same<SeedSequence, pcg_engine>::value>>
+ explicit pcg_engine(SeedSequence&& seq) {
+ seed(seq);
+ }
+
+ pcg_engine(const pcg_engine&) = default;
+ pcg_engine& operator=(const pcg_engine&) = default;
+ pcg_engine(pcg_engine&&) = default;
+ pcg_engine& operator=(pcg_engine&&) = default;
+
+ result_type operator()() {
+ // Advance the LCG state, always using the new value to generate the output.
+ state_ = lcg(state_);
+ return Mix{}(state_);
+ }
+
+ void seed(uint64_t seed_value = 0) {
+ state_type tmp = seed_value;
+ state_ = lcg(tmp + Params::increment());
+ }
+
+ template <class SeedSequence>
+ typename absl::enable_if_t<
+ !std::is_convertible<SeedSequence, uint64_t>::value, void>
+ seed(SeedSequence&& seq) {
+ reseed(seq);
+ }
+
+ void discard(uint64_t count) { state_ = advance(state_, count); }
+
+ bool operator==(const pcg_engine& other) const {
+ return state_ == other.state_;
+ }
+
+ bool operator!=(const pcg_engine& other) const { return !(*this == other); }
+
+ template <class CharT, class Traits>
+ friend typename absl::enable_if_t<(sizeof(state_type) == 16),
+ std::basic_ostream<CharT, Traits>&>
+ operator<<(
+ std::basic_ostream<CharT, Traits>& os, // NOLINT(runtime/references)
+ const pcg_engine& engine) {
+ auto saver = random_internal::make_ostream_state_saver(os);
+ random_internal::stream_u128_helper<state_type> helper;
+ helper.write(pcg_engine::params_type::multiplier(), os);
+ os << os.fill();
+ helper.write(pcg_engine::params_type::increment(), os);
+ os << os.fill();
+ helper.write(engine.state_, os);
+ return os;
+ }
+
+ template <class CharT, class Traits>
+ friend typename absl::enable_if_t<(sizeof(state_type) <= 8),
+ std::basic_ostream<CharT, Traits>&>
+ operator<<(
+ std::basic_ostream<CharT, Traits>& os, // NOLINT(runtime/references)
+ const pcg_engine& engine) {
+ auto saver = random_internal::make_ostream_state_saver(os);
+ os << pcg_engine::params_type::multiplier() << os.fill();
+ os << pcg_engine::params_type::increment() << os.fill();
+ os << engine.state_;
+ return os;
+ }
+
+ template <class CharT, class Traits>
+ friend typename absl::enable_if_t<(sizeof(state_type) == 16),
+ std::basic_istream<CharT, Traits>&>
+ operator>>(
+ std::basic_istream<CharT, Traits>& is, // NOLINT(runtime/references)
+ pcg_engine& engine) { // NOLINT(runtime/references)
+ random_internal::stream_u128_helper<state_type> helper;
+ auto mult = helper.read(is);
+ auto inc = helper.read(is);
+ auto tmp = helper.read(is);
+ if (mult != pcg_engine::params_type::multiplier() ||
+ inc != pcg_engine::params_type::increment()) {
+ // signal failure by setting the failbit.
+ is.setstate(is.rdstate() | std::ios_base::failbit);
+ }
+ if (!is.fail()) {
+ engine.state_ = tmp;
+ }
+ return is;
+ }
+
+ template <class CharT, class Traits>
+ friend typename absl::enable_if_t<(sizeof(state_type) <= 8),
+ std::basic_istream<CharT, Traits>&>
+ operator>>(
+ std::basic_istream<CharT, Traits>& is, // NOLINT(runtime/references)
+ pcg_engine& engine) { // NOLINT(runtime/references)
+ state_type mult{}, inc{}, tmp{};
+ is >> mult >> inc >> tmp;
+ if (mult != pcg_engine::params_type::multiplier() ||
+ inc != pcg_engine::params_type::increment()) {
+ // signal failure by setting the failbit.
+ is.setstate(is.rdstate() | std::ios_base::failbit);
+ }
+ if (!is.fail()) {
+ engine.state_ = tmp;
+ }
+ return is;
+ }
+
+ private:
+ state_type state_;
+
+ // Returns the linear-congruential generator next state.
+ static inline constexpr state_type lcg(state_type s) {
+ return s * Params::multiplier() + Params::increment();
+ }
+
+ // Returns the linear-congruential arbitrary seek state.
+ inline state_type advance(state_type s, uint64_t n) const {
+ state_type mult = Params::multiplier();
+ state_type inc = Params::increment();
+ state_type m = 1;
+ state_type i = 0;
+ while (n > 0) {
+ if (n & 1) {
+ m *= mult;
+ i = i * mult + inc;
+ }
+ inc = (mult + 1) * inc;
+ mult *= mult;
+ n >>= 1;
+ }
+ return m * s + i;
+ }
+
+ template <class SeedSequence>
+ void reseed(SeedSequence& seq) {
+ using sequence_result_type = typename SeedSequence::result_type;
+ constexpr size_t kBufferSize =
+ sizeof(state_type) / sizeof(sequence_result_type);
+ sequence_result_type buffer[kBufferSize];
+ seq.generate(std::begin(buffer), std::end(buffer));
+ // Convert the seed output to a single state value.
+ state_type tmp = buffer[0];
+ for (size_t i = 1; i < kBufferSize; i++) {
+ tmp <<= (sizeof(sequence_result_type) * 8);
+ tmp |= buffer[i];
+ }
+ state_ = lcg(tmp + params_type::increment());
+ }
+};
+
+// Parameterized implementation of the PCG 128-bit oneseq state.
+// This provides state_type, multiplier, and increment for pcg_engine.
+template <uint64_t kMultA, uint64_t kMultB, uint64_t kIncA, uint64_t kIncB>
+class pcg128_params {
+ public:
+#if ABSL_HAVE_INTRINSIC_INT128
+ using state_type = __uint128_t;
+ static inline constexpr state_type make_u128(uint64_t a, uint64_t b) {
+ return (static_cast<__uint128_t>(a) << 64) | b;
+ }
+#else
+ using state_type = absl::uint128;
+ static inline constexpr state_type make_u128(uint64_t a, uint64_t b) {
+ return absl::MakeUint128(a, b);
+ }
+#endif
+
+ static inline constexpr state_type multiplier() {
+ return make_u128(kMultA, kMultB);
+ }
+ static inline constexpr state_type increment() {
+ return make_u128(kIncA, kIncB);
+ }
+};
+
+// Implementation of the PCG xsl_rr_128_64 128-bit mixing function, which
+// accepts an input of state_type and mixes it into an output of result_type.
+struct pcg_xsl_rr_128_64 {
+#if ABSL_HAVE_INTRINSIC_INT128
+ using state_type = __uint128_t;
+#else
+ using state_type = absl::uint128;
+#endif
+ using result_type = uint64_t;
+
+ inline uint64_t operator()(state_type state) {
+ // This is equivalent to the xsl_rr_128_64 mixing function.
+#if ABSL_HAVE_INTRINSIC_INT128
+ uint64_t rotate = static_cast<uint64_t>(state >> 122u);
+ state ^= state >> 64;
+ uint64_t s = static_cast<uint64_t>(state);
+#else
+ uint64_t h = Uint128High64(state);
+ uint64_t rotate = h >> 58u;
+ uint64_t s = Uint128Low64(state) ^ h;
+#endif
+ return random_internal::rotr(s, rotate);
+ }
+};
+
+// Parameterized implementation of the PCG 64-bit oneseq state.
+// This provides state_type, multiplier, and increment for pcg_engine.
+template <uint64_t kMult, uint64_t kInc>
+class pcg64_params {
+ public:
+ using state_type = uint64_t;
+ static inline constexpr state_type multiplier() { return kMult; }
+ static inline constexpr state_type increment() { return kInc; }
+};
+
+// Implementation of the PCG xsh_rr_64_32 64-bit mixing function, which accepts
+// an input of state_type and mixes it into an output of result_type.
+struct pcg_xsh_rr_64_32 {
+ using state_type = uint64_t;
+ using result_type = uint32_t;
+ inline uint32_t operator()(uint64_t state) {
+ return random_internal::rotr(
+ static_cast<uint32_t>(((state >> 18) ^ state) >> 27), state >> 59);
+ }
+};
+
+// Stable pcg_engine implementations:
+// This is a 64-bit generator using 128-bits of state.
+// The output sequence is equivalent to Melissa O'Neil's pcg64_oneseq.
+using pcg64_2018_engine = pcg_engine<
+ random_internal::pcg128_params<0x2360ed051fc65da4ull, 0x4385df649fccf645ull,
+ 0x5851f42d4c957f2d, 0x14057b7ef767814f>,
+ random_internal::pcg_xsl_rr_128_64>;
+
+// This is a 32-bit generator using 64-bits of state.
+// This is equivalent to Melissa O'Neil's pcg32_oneseq.
+using pcg32_2018_engine = pcg_engine<
+ random_internal::pcg64_params<0x5851f42d4c957f2dull, 0x14057b7ef767814full>,
+ random_internal::pcg_xsh_rr_64_32>;
+
+} // namespace random_internal
+} // namespace absl
+
+#endif // ABSL_RANDOM_PCG2018_ENGINE_H_
git://repos.xcallymotion.com / motion2.git / blobdiff