181 lines
6.7 KiB
C++
181 lines
6.7 KiB
C++
//
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// Copyright 2018 The Abseil Authors.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// https://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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//
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// -----------------------------------------------------------------------------
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// File: bit_gen_ref.h
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// -----------------------------------------------------------------------------
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//
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// This header defines a bit generator "reference" class, for use in interfaces
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// that take both Abseil (e.g. `absl::BitGen`) and standard library (e.g.
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// `std::mt19937`) bit generators.
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#ifndef ABSL_RANDOM_BIT_GEN_REF_H_
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#define ABSL_RANDOM_BIT_GEN_REF_H_
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#include "absl/base/internal/fast_type_id.h"
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#include "absl/base/macros.h"
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#include "absl/meta/type_traits.h"
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#include "absl/random/internal/distribution_caller.h"
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#include "absl/random/internal/fast_uniform_bits.h"
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namespace absl {
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ABSL_NAMESPACE_BEGIN
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namespace random_internal {
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template <typename URBG, typename = void, typename = void, typename = void>
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struct is_urbg : std::false_type {};
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template <typename URBG>
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struct is_urbg<
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URBG,
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absl::enable_if_t<std::is_same<
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typename URBG::result_type,
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typename std::decay<decltype((URBG::min)())>::type>::value>,
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absl::enable_if_t<std::is_same<
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typename URBG::result_type,
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typename std::decay<decltype((URBG::max)())>::type>::value>,
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absl::enable_if_t<std::is_same<
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typename URBG::result_type,
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typename std::decay<decltype(std::declval<URBG>()())>::type>::value>>
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: std::true_type {};
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template <typename>
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struct DistributionCaller;
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class MockHelpers;
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} // namespace random_internal
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// -----------------------------------------------------------------------------
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// absl::BitGenRef
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// -----------------------------------------------------------------------------
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//
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// `absl::BitGenRef` is a type-erasing class that provides a generator-agnostic
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// non-owning "reference" interface for use in place of any specific uniform
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// random bit generator (URBG). This class may be used for both Abseil
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// (e.g. `absl::BitGen`, `absl::InsecureBitGen`) and Standard library (e.g
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// `std::mt19937`, `std::minstd_rand`) bit generators.
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//
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// Like other reference classes, `absl::BitGenRef` does not own the
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// underlying bit generator, and the underlying instance must outlive the
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// `absl::BitGenRef`.
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//
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// `absl::BitGenRef` is particularly useful when used with an
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// `absl::MockingBitGen` to test specific paths in functions which use random
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// values.
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//
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// Example:
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// void TakesBitGenRef(absl::BitGenRef gen) {
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// int x = absl::Uniform<int>(gen, 0, 1000);
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// }
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//
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class BitGenRef {
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// SFINAE to detect whether the URBG type includes a member matching
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// bool InvokeMock(base_internal::FastTypeIdType, void*, void*).
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//
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// These live inside BitGenRef so that they have friend access
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// to MockingBitGen. (see similar methods in DistributionCaller).
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template <template <class...> class Trait, class AlwaysVoid, class... Args>
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struct detector : std::false_type {};
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template <template <class...> class Trait, class... Args>
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struct detector<Trait, absl::void_t<Trait<Args...>>, Args...>
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: std::true_type {};
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template <class T>
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using invoke_mock_t = decltype(std::declval<T*>()->InvokeMock(
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std::declval<base_internal::FastTypeIdType>(), std::declval<void*>(),
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std::declval<void*>()));
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template <typename T>
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using HasInvokeMock = typename detector<invoke_mock_t, void, T>::type;
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public:
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BitGenRef(const BitGenRef&) = default;
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BitGenRef(BitGenRef&&) = default;
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BitGenRef& operator=(const BitGenRef&) = default;
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BitGenRef& operator=(BitGenRef&&) = default;
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template <typename URBG, typename absl::enable_if_t<
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(!std::is_same<URBG, BitGenRef>::value &&
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random_internal::is_urbg<URBG>::value &&
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!HasInvokeMock<URBG>::value)>* = nullptr>
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BitGenRef(URBG& gen) // NOLINT
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: t_erased_gen_ptr_(reinterpret_cast<uintptr_t>(&gen)),
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mock_call_(NotAMock),
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generate_impl_fn_(ImplFn<URBG>) {}
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template <typename URBG,
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typename absl::enable_if_t<(!std::is_same<URBG, BitGenRef>::value &&
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random_internal::is_urbg<URBG>::value &&
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HasInvokeMock<URBG>::value)>* = nullptr>
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BitGenRef(URBG& gen) // NOLINT
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: t_erased_gen_ptr_(reinterpret_cast<uintptr_t>(&gen)),
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mock_call_(&MockCall<URBG>),
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generate_impl_fn_(ImplFn<URBG>) {}
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using result_type = uint64_t;
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static constexpr result_type(min)() {
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return (std::numeric_limits<result_type>::min)();
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}
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static constexpr result_type(max)() {
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return (std::numeric_limits<result_type>::max)();
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}
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result_type operator()() { return generate_impl_fn_(t_erased_gen_ptr_); }
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private:
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using impl_fn = result_type (*)(uintptr_t);
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using mock_call_fn = bool (*)(uintptr_t, base_internal::FastTypeIdType, void*,
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void*);
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template <typename URBG>
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static result_type ImplFn(uintptr_t ptr) {
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// Ensure that the return values from operator() fill the entire
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// range promised by result_type, min() and max().
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absl::random_internal::FastUniformBits<result_type> fast_uniform_bits;
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return fast_uniform_bits(*reinterpret_cast<URBG*>(ptr));
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}
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// Get a type-erased InvokeMock pointer.
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template <typename URBG>
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static bool MockCall(uintptr_t gen_ptr, base_internal::FastTypeIdType type,
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void* result, void* arg_tuple) {
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return reinterpret_cast<URBG*>(gen_ptr)->InvokeMock(type, result,
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arg_tuple);
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}
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static bool NotAMock(uintptr_t, base_internal::FastTypeIdType, void*, void*) {
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return false;
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}
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inline bool InvokeMock(base_internal::FastTypeIdType type, void* args_tuple,
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void* result) {
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if (mock_call_ == NotAMock) return false; // avoids an indirect call.
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return mock_call_(t_erased_gen_ptr_, type, args_tuple, result);
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}
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uintptr_t t_erased_gen_ptr_;
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mock_call_fn mock_call_;
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impl_fn generate_impl_fn_;
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template <typename>
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friend struct ::absl::random_internal::DistributionCaller; // for InvokeMock
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friend class ::absl::random_internal::MockHelpers; // for InvokeMock
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};
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ABSL_NAMESPACE_END
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} // namespace absl
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#endif // ABSL_RANDOM_BIT_GEN_REF_H_
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