diff options
Diffstat (limited to 'third_party/abseil_cpp/absl/random/bit_gen_ref.h')
-rw-r--r-- | third_party/abseil_cpp/absl/random/bit_gen_ref.h | 181 |
1 files changed, 181 insertions, 0 deletions
diff --git a/third_party/abseil_cpp/absl/random/bit_gen_ref.h b/third_party/abseil_cpp/absl/random/bit_gen_ref.h new file mode 100644 index 000000000000..9555460fd491 --- /dev/null +++ b/third_party/abseil_cpp/absl/random/bit_gen_ref.h @@ -0,0 +1,181 @@ +// +// 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. +// +// ----------------------------------------------------------------------------- +// File: bit_gen_ref.h +// ----------------------------------------------------------------------------- +// +// This header defines a bit generator "reference" class, for use in interfaces +// that take both Abseil (e.g. `absl::BitGen`) and standard library (e.g. +// `std::mt19937`) bit generators. + +#ifndef ABSL_RANDOM_BIT_GEN_REF_H_ +#define ABSL_RANDOM_BIT_GEN_REF_H_ + +#include "absl/base/internal/fast_type_id.h" +#include "absl/base/macros.h" +#include "absl/meta/type_traits.h" +#include "absl/random/internal/distribution_caller.h" +#include "absl/random/internal/fast_uniform_bits.h" + +namespace absl { +ABSL_NAMESPACE_BEGIN +namespace random_internal { + +template <typename URBG, typename = void, typename = void, typename = void> +struct is_urbg : std::false_type {}; + +template <typename URBG> +struct is_urbg< + URBG, + absl::enable_if_t<std::is_same< + typename URBG::result_type, + typename std::decay<decltype((URBG::min)())>::type>::value>, + absl::enable_if_t<std::is_same< + typename URBG::result_type, + typename std::decay<decltype((URBG::max)())>::type>::value>, + absl::enable_if_t<std::is_same< + typename URBG::result_type, + typename std::decay<decltype(std::declval<URBG>()())>::type>::value>> + : std::true_type {}; + +template <typename> +struct DistributionCaller; +class MockHelpers; + +} // namespace random_internal + +// ----------------------------------------------------------------------------- +// absl::BitGenRef +// ----------------------------------------------------------------------------- +// +// `absl::BitGenRef` is a type-erasing class that provides a generator-agnostic +// non-owning "reference" interface for use in place of any specific uniform +// random bit generator (URBG). This class may be used for both Abseil +// (e.g. `absl::BitGen`, `absl::InsecureBitGen`) and Standard library (e.g +// `std::mt19937`, `std::minstd_rand`) bit generators. +// +// Like other reference classes, `absl::BitGenRef` does not own the +// underlying bit generator, and the underlying instance must outlive the +// `absl::BitGenRef`. +// +// `absl::BitGenRef` is particularly useful when used with an +// `absl::MockingBitGen` to test specific paths in functions which use random +// values. +// +// Example: +// void TakesBitGenRef(absl::BitGenRef gen) { +// int x = absl::Uniform<int>(gen, 0, 1000); +// } +// +class BitGenRef { + // SFINAE to detect whether the URBG type includes a member matching + // bool InvokeMock(base_internal::FastTypeIdType, void*, void*). + // + // These live inside BitGenRef so that they have friend access + // to MockingBitGen. (see similar methods in DistributionCaller). + template <template <class...> class Trait, class AlwaysVoid, class... Args> + struct detector : std::false_type {}; + template <template <class...> class Trait, class... Args> + struct detector<Trait, absl::void_t<Trait<Args...>>, Args...> + : std::true_type {}; + + template <class T> + using invoke_mock_t = decltype(std::declval<T*>()->InvokeMock( + std::declval<base_internal::FastTypeIdType>(), std::declval<void*>(), + std::declval<void*>())); + + template <typename T> + using HasInvokeMock = typename detector<invoke_mock_t, void, T>::type; + + public: + BitGenRef(const BitGenRef&) = default; + BitGenRef(BitGenRef&&) = default; + BitGenRef& operator=(const BitGenRef&) = default; + BitGenRef& operator=(BitGenRef&&) = default; + + template <typename URBG, typename absl::enable_if_t< + (!std::is_same<URBG, BitGenRef>::value && + random_internal::is_urbg<URBG>::value && + !HasInvokeMock<URBG>::value)>* = nullptr> + BitGenRef(URBG& gen) // NOLINT + : t_erased_gen_ptr_(reinterpret_cast<uintptr_t>(&gen)), + mock_call_(NotAMock), + generate_impl_fn_(ImplFn<URBG>) {} + + template <typename URBG, + typename absl::enable_if_t<(!std::is_same<URBG, BitGenRef>::value && + random_internal::is_urbg<URBG>::value && + HasInvokeMock<URBG>::value)>* = nullptr> + BitGenRef(URBG& gen) // NOLINT + : t_erased_gen_ptr_(reinterpret_cast<uintptr_t>(&gen)), + mock_call_(&MockCall<URBG>), + generate_impl_fn_(ImplFn<URBG>) {} + + 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 generate_impl_fn_(t_erased_gen_ptr_); } + + private: + using impl_fn = result_type (*)(uintptr_t); + using mock_call_fn = bool (*)(uintptr_t, base_internal::FastTypeIdType, void*, + void*); + + template <typename URBG> + static result_type ImplFn(uintptr_t ptr) { + // Ensure that the return values from operator() fill the entire + // range promised by result_type, min() and max(). + absl::random_internal::FastUniformBits<result_type> fast_uniform_bits; + return fast_uniform_bits(*reinterpret_cast<URBG*>(ptr)); + } + + // Get a type-erased InvokeMock pointer. + template <typename URBG> + static bool MockCall(uintptr_t gen_ptr, base_internal::FastTypeIdType type, + void* result, void* arg_tuple) { + return reinterpret_cast<URBG*>(gen_ptr)->InvokeMock(type, result, + arg_tuple); + } + static bool NotAMock(uintptr_t, base_internal::FastTypeIdType, void*, void*) { + return false; + } + + inline bool InvokeMock(base_internal::FastTypeIdType type, void* args_tuple, + void* result) { + if (mock_call_ == NotAMock) return false; // avoids an indirect call. + return mock_call_(t_erased_gen_ptr_, type, args_tuple, result); + } + + uintptr_t t_erased_gen_ptr_; + mock_call_fn mock_call_; + impl_fn generate_impl_fn_; + + template <typename> + friend struct ::absl::random_internal::DistributionCaller; // for InvokeMock + friend class ::absl::random_internal::MockHelpers; // for InvokeMock +}; + +ABSL_NAMESPACE_END +} // namespace absl + +#endif // ABSL_RANDOM_BIT_GEN_REF_H_ |