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/*
* Copyright 2021 Google Inc. All rights reserved.
*
* 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
*
* http://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 FLATBUFFERS_ARRAY_H_
#define FLATBUFFERS_ARRAY_H_
#include <cstdint>
#include <memory>
#include "flatbuffers/base.h"
#include "flatbuffers/stl_emulation.h"
#include "flatbuffers/vector.h"
namespace flatbuffers {
// This is used as a helper type for accessing arrays.
template<typename T, uint16_t length> class Array {
// Array<T> can carry only POD data types (scalars or structs).
typedef typename flatbuffers::bool_constant<flatbuffers::is_scalar<T>::value>
scalar_tag;
typedef
typename flatbuffers::conditional<scalar_tag::value, T, const T *>::type
IndirectHelperType;
public:
typedef uint16_t size_type;
typedef typename IndirectHelper<IndirectHelperType>::return_type return_type;
typedef VectorConstIterator<T, return_type, uoffset_t> const_iterator;
typedef VectorReverseIterator<const_iterator> const_reverse_iterator;
// If T is a LE-scalar or a struct (!scalar_tag::value).
static FLATBUFFERS_CONSTEXPR bool is_span_observable =
(scalar_tag::value && (FLATBUFFERS_LITTLEENDIAN || sizeof(T) == 1)) ||
!scalar_tag::value;
FLATBUFFERS_CONSTEXPR uint16_t size() const { return length; }
return_type Get(uoffset_t i) const {
FLATBUFFERS_ASSERT(i < size());
return IndirectHelper<IndirectHelperType>::Read(Data(), i);
}
return_type operator[](uoffset_t i) const { return Get(i); }
// If this is a Vector of enums, T will be its storage type, not the enum
// type. This function makes it convenient to retrieve value with enum
// type E.
template<typename E> E GetEnum(uoffset_t i) const {
return static_cast<E>(Get(i));
}
const_iterator begin() const { return const_iterator(Data(), 0); }
const_iterator end() const { return const_iterator(Data(), size()); }
const_reverse_iterator rbegin() const {
return const_reverse_iterator(end());
}
const_reverse_iterator rend() const {
return const_reverse_iterator(begin());
}
const_iterator cbegin() const { return begin(); }
const_iterator cend() const { return end(); }
const_reverse_iterator crbegin() const { return rbegin(); }
const_reverse_iterator crend() const { return rend(); }
// Get a mutable pointer to elements inside this array.
// This method used to mutate arrays of structs followed by a @p Mutate
// operation. For primitive types use @p Mutate directly.
// @warning Assignments and reads to/from the dereferenced pointer are not
// automatically converted to the correct endianness.
typename flatbuffers::conditional<scalar_tag::value, void, T *>::type
GetMutablePointer(uoffset_t i) const {
FLATBUFFERS_ASSERT(i < size());
return const_cast<T *>(&data()[i]);
}
// Change elements if you have a non-const pointer to this object.
void Mutate(uoffset_t i, const T &val) { MutateImpl(scalar_tag(), i, val); }
// The raw data in little endian format. Use with care.
const uint8_t *Data() const { return data_; }
uint8_t *Data() { return data_; }
// Similarly, but typed, much like std::vector::data
const T *data() const { return reinterpret_cast<const T *>(Data()); }
T *data() { return reinterpret_cast<T *>(Data()); }
// Copy data from a span with endian conversion.
// If this Array and the span overlap, the behavior is undefined.
void CopyFromSpan(flatbuffers::span<const T, length> src) {
const auto p1 = reinterpret_cast<const uint8_t *>(src.data());
const auto p2 = Data();
FLATBUFFERS_ASSERT(!(p1 >= p2 && p1 < (p2 + length)) &&
!(p2 >= p1 && p2 < (p1 + length)));
(void)p1;
(void)p2;
CopyFromSpanImpl(flatbuffers::bool_constant<is_span_observable>(), src);
}
protected:
void MutateImpl(flatbuffers::true_type, uoffset_t i, const T &val) {
FLATBUFFERS_ASSERT(i < size());
WriteScalar(data() + i, val);
}
void MutateImpl(flatbuffers::false_type, uoffset_t i, const T &val) {
*(GetMutablePointer(i)) = val;
}
void CopyFromSpanImpl(flatbuffers::true_type,
flatbuffers::span<const T, length> src) {
// Use std::memcpy() instead of std::copy() to avoid performance degradation
// due to aliasing if T is char or unsigned char.
// The size is known at compile time, so memcpy would be inlined.
std::memcpy(data(), src.data(), length * sizeof(T));
}
// Copy data from flatbuffers::span with endian conversion.
void CopyFromSpanImpl(flatbuffers::false_type,
flatbuffers::span<const T, length> src) {
for (size_type k = 0; k < length; k++) { Mutate(k, src[k]); }
}
// This class is only used to access pre-existing data. Don't ever
// try to construct these manually.
// 'constexpr' allows us to use 'size()' at compile time.
// @note Must not use 'FLATBUFFERS_CONSTEXPR' here, as const is not allowed on
// a constructor.
#if defined(__cpp_constexpr)
constexpr Array();
#else
Array();
#endif
uint8_t data_[length * sizeof(T)];
private:
// This class is a pointer. Copying will therefore create an invalid object.
// Private and unimplemented copy constructor.
Array(const Array &);
Array &operator=(const Array &);
};
// Specialization for Array[struct] with access using Offset<void> pointer.
// This specialization used by idl_gen_text.cpp.
template<typename T, uint16_t length, template<typename> class OffsetT>
class Array<OffsetT<T>, length> {
static_assert(flatbuffers::is_same<T, void>::value, "unexpected type T");
public:
typedef const void *return_type;
typedef uint16_t size_type;
const uint8_t *Data() const { return data_; }
// Make idl_gen_text.cpp::PrintContainer happy.
return_type operator[](uoffset_t) const {
FLATBUFFERS_ASSERT(false);
return nullptr;
}
private:
// This class is only used to access pre-existing data.
Array();
Array(const Array &);
Array &operator=(const Array &);
uint8_t data_[1];
};
template<class U, uint16_t N>
FLATBUFFERS_CONSTEXPR_CPP11 flatbuffers::span<U, N> make_span(Array<U, N> &arr)
FLATBUFFERS_NOEXCEPT {
static_assert(
Array<U, N>::is_span_observable,
"wrong type U, only plain struct, LE-scalar, or byte types are allowed");
return span<U, N>(arr.data(), N);
}
template<class U, uint16_t N>
FLATBUFFERS_CONSTEXPR_CPP11 flatbuffers::span<const U, N> make_span(
const Array<U, N> &arr) FLATBUFFERS_NOEXCEPT {
static_assert(
Array<U, N>::is_span_observable,
"wrong type U, only plain struct, LE-scalar, or byte types are allowed");
return span<const U, N>(arr.data(), N);
}
template<class U, uint16_t N>
FLATBUFFERS_CONSTEXPR_CPP11 flatbuffers::span<uint8_t, sizeof(U) * N>
make_bytes_span(Array<U, N> &arr) FLATBUFFERS_NOEXCEPT {
static_assert(Array<U, N>::is_span_observable,
"internal error, Array<T> might hold only scalars or structs");
return span<uint8_t, sizeof(U) * N>(arr.Data(), sizeof(U) * N);
}
template<class U, uint16_t N>
FLATBUFFERS_CONSTEXPR_CPP11 flatbuffers::span<const uint8_t, sizeof(U) * N>
make_bytes_span(const Array<U, N> &arr) FLATBUFFERS_NOEXCEPT {
static_assert(Array<U, N>::is_span_observable,
"internal error, Array<T> might hold only scalars or structs");
return span<const uint8_t, sizeof(U) * N>(arr.Data(), sizeof(U) * N);
}
// Cast a raw T[length] to a raw flatbuffers::Array<T, length>
// without endian conversion. Use with care.
// TODO: move these Cast-methods to `internal` namespace.
template<typename T, uint16_t length>
Array<T, length> &CastToArray(T (&arr)[length]) {
return *reinterpret_cast<Array<T, length> *>(arr);
}
template<typename T, uint16_t length>
const Array<T, length> &CastToArray(const T (&arr)[length]) {
return *reinterpret_cast<const Array<T, length> *>(arr);
}
template<typename E, typename T, uint16_t length>
Array<E, length> &CastToArrayOfEnum(T (&arr)[length]) {
static_assert(sizeof(E) == sizeof(T), "invalid enum type E");
return *reinterpret_cast<Array<E, length> *>(arr);
}
template<typename E, typename T, uint16_t length>
const Array<E, length> &CastToArrayOfEnum(const T (&arr)[length]) {
static_assert(sizeof(E) == sizeof(T), "invalid enum type E");
return *reinterpret_cast<const Array<E, length> *>(arr);
}
template<typename T, uint16_t length>
bool operator==(const Array<T, length> &lhs,
const Array<T, length> &rhs) noexcept {
return std::addressof(lhs) == std::addressof(rhs) ||
(lhs.size() == rhs.size() &&
std::memcmp(lhs.Data(), rhs.Data(), rhs.size() * sizeof(T)) == 0);
}
} // namespace flatbuffers
#endif // FLATBUFFERS_ARRAY_H_