--- /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.
+//
+// MOTIVATION AND TUTORIAL
+//
+// If you want to put in a single heap allocation N doubles followed by M ints,
+// it's easy if N and M are known at compile time.
+//
+// struct S {
+// double a[N];
+// int b[M];
+// };
+//
+// S* p = new S;
+//
+// But what if N and M are known only in run time? Class template Layout to the
+// rescue! It's a portable generalization of the technique known as struct hack.
+//
+// // This object will tell us everything we need to know about the memory
+// // layout of double[N] followed by int[M]. It's structurally identical to
+// // size_t[2] that stores N and M. It's very cheap to create.
+// const Layout<double, int> layout(N, M);
+//
+// // Allocate enough memory for both arrays. `AllocSize()` tells us how much
+// // memory is needed. We are free to use any allocation function we want as
+// // long as it returns aligned memory.
+// std::unique_ptr<unsigned char[]> p(new unsigned char[layout.AllocSize()]);
+//
+// // Obtain the pointer to the array of doubles.
+// // Equivalent to `reinterpret_cast<double*>(p.get())`.
+// //
+// // We could have written layout.Pointer<0>(p) instead. If all the types are
+// // unique you can use either form, but if some types are repeated you must
+// // use the index form.
+// double* a = layout.Pointer<double>(p.get());
+//
+// // Obtain the pointer to the array of ints.
+// // Equivalent to `reinterpret_cast<int*>(p.get() + N * 8)`.
+// int* b = layout.Pointer<int>(p);
+//
+// If we are unable to specify sizes of all fields, we can pass as many sizes as
+// we can to `Partial()`. In return, it'll allow us to access the fields whose
+// locations and sizes can be computed from the provided information.
+// `Partial()` comes in handy when the array sizes are embedded into the
+// allocation.
+//
+// // size_t[1] containing N, size_t[1] containing M, double[N], int[M].
+// using L = Layout<size_t, size_t, double, int>;
+//
+// unsigned char* Allocate(size_t n, size_t m) {
+// const L layout(1, 1, n, m);
+// unsigned char* p = new unsigned char[layout.AllocSize()];
+// *layout.Pointer<0>(p) = n;
+// *layout.Pointer<1>(p) = m;
+// return p;
+// }
+//
+// void Use(unsigned char* p) {
+// // First, extract N and M.
+// // Specify that the first array has only one element. Using `prefix` we
+// // can access the first two arrays but not more.
+// constexpr auto prefix = L::Partial(1);
+// size_t n = *prefix.Pointer<0>(p);
+// size_t m = *prefix.Pointer<1>(p);
+//
+// // Now we can get pointers to the payload.
+// const L layout(1, 1, n, m);
+// double* a = layout.Pointer<double>(p);
+// int* b = layout.Pointer<int>(p);
+// }
+//
+// The layout we used above combines fixed-size with dynamically-sized fields.
+// This is quite common. Layout is optimized for this use case and generates
+// optimal code. All computations that can be performed at compile time are
+// indeed performed at compile time.
+//
+// Efficiency tip: The order of fields matters. In `Layout<T1, ..., TN>` try to
+// ensure that `alignof(T1) >= ... >= alignof(TN)`. This way you'll have no
+// padding in between arrays.
+//
+// You can manually override the alignment of an array by wrapping the type in
+// `Aligned<T, N>`. `Layout<..., Aligned<T, N>, ...>` has exactly the same API
+// and behavior as `Layout<..., T, ...>` except that the first element of the
+// array of `T` is aligned to `N` (the rest of the elements follow without
+// padding). `N` cannot be less than `alignof(T)`.
+//
+// `AllocSize()` and `Pointer()` are the most basic methods for dealing with
+// memory layouts. Check out the reference or code below to discover more.
+//
+// EXAMPLE
+//
+// // Immutable move-only string with sizeof equal to sizeof(void*). The
+// // string size and the characters are kept in the same heap allocation.
+// class CompactString {
+// public:
+// CompactString(const char* s = "") {
+// const size_t size = strlen(s);
+// // size_t[1] followed by char[size + 1].
+// const L layout(1, size + 1);
+// p_.reset(new unsigned char[layout.AllocSize()]);
+// // If running under ASAN, mark the padding bytes, if any, to catch
+// // memory errors.
+// layout.PoisonPadding(p_.get());
+// // Store the size in the allocation.
+// *layout.Pointer<size_t>(p_.get()) = size;
+// // Store the characters in the allocation.
+// memcpy(layout.Pointer<char>(p_.get()), s, size + 1);
+// }
+//
+// size_t size() const {
+// // Equivalent to reinterpret_cast<size_t&>(*p).
+// return *L::Partial().Pointer<size_t>(p_.get());
+// }
+//
+// const char* c_str() const {
+// // Equivalent to reinterpret_cast<char*>(p.get() + sizeof(size_t)).
+// // The argument in Partial(1) specifies that we have size_t[1] in front
+// // of the characters.
+// return L::Partial(1).Pointer<char>(p_.get());
+// }
+//
+// private:
+// // Our heap allocation contains a size_t followed by an array of chars.
+// using L = Layout<size_t, char>;
+// std::unique_ptr<unsigned char[]> p_;
+// };
+//
+// int main() {
+// CompactString s = "hello";
+// assert(s.size() == 5);
+// assert(strcmp(s.c_str(), "hello") == 0);
+// }
+//
+// DOCUMENTATION
+//
+// The interface exported by this file consists of:
+// - class `Layout<>` and its public members.
+// - The public members of class `internal_layout::LayoutImpl<>`. That class
+// isn't intended to be used directly, and its name and template parameter
+// list are internal implementation details, but the class itself provides
+// most of the functionality in this file. See comments on its members for
+// detailed documentation.
+//
+// `Layout<T1,... Tn>::Partial(count1,..., countm)` (where `m` <= `n`) returns a
+// `LayoutImpl<>` object. `Layout<T1,..., Tn> layout(count1,..., countn)`
+// creates a `Layout` object, which exposes the same functionality by inheriting
+// from `LayoutImpl<>`.
+
+#ifndef ABSL_CONTAINER_INTERNAL_LAYOUT_H_
+#define ABSL_CONTAINER_INTERNAL_LAYOUT_H_
+
+#include <assert.h>
+#include <stddef.h>
+#include <stdint.h>
+#include <ostream>
+#include <string>
+#include <tuple>
+#include <type_traits>
+#include <typeinfo>
+#include <utility>
+
+#ifdef ADDRESS_SANITIZER
+#include <sanitizer/asan_interface.h>
+#endif
+
+#include "absl/meta/type_traits.h"
+#include "absl/strings/str_cat.h"
+#include "absl/types/span.h"
+#include "absl/utility/utility.h"
+
+#if defined(__GXX_RTTI)
+#define ABSL_INTERNAL_HAS_CXA_DEMANGLE
+#endif
+
+#ifdef ABSL_INTERNAL_HAS_CXA_DEMANGLE
+#include <cxxabi.h>
+#endif
+
+namespace absl {
+namespace container_internal {
+
+// A type wrapper that instructs `Layout` to use the specific alignment for the
+// array. `Layout<..., Aligned<T, N>, ...>` has exactly the same API
+// and behavior as `Layout<..., T, ...>` except that the first element of the
+// array of `T` is aligned to `N` (the rest of the elements follow without
+// padding).
+//
+// Requires: `N >= alignof(T)` and `N` is a power of 2.
+template <class T, size_t N>
+struct Aligned;
+
+namespace internal_layout {
+
+template <class T>
+struct NotAligned {};
+
+template <class T, size_t N>
+struct NotAligned<const Aligned<T, N>> {
+ static_assert(sizeof(T) == 0, "Aligned<T, N> cannot be const-qualified");
+};
+
+template <size_t>
+using IntToSize = size_t;
+
+template <class>
+using TypeToSize = size_t;
+
+template <class T>
+struct Type : NotAligned<T> {
+ using type = T;
+};
+
+template <class T, size_t N>
+struct Type<Aligned<T, N>> {
+ using type = T;
+};
+
+template <class T>
+struct SizeOf : NotAligned<T>, std::integral_constant<size_t, sizeof(T)> {};
+
+template <class T, size_t N>
+struct SizeOf<Aligned<T, N>> : std::integral_constant<size_t, sizeof(T)> {};
+
+// Note: workaround for https://gcc.gnu.org/PR88115
+template <class T>
+struct AlignOf : NotAligned<T> {
+ static constexpr size_t value = alignof(T);
+};
+
+template <class T, size_t N>
+struct AlignOf<Aligned<T, N>> {
+ static_assert(N % alignof(T) == 0,
+ "Custom alignment can't be lower than the type's alignment");
+ static constexpr size_t value = N;
+};
+
+// Does `Ts...` contain `T`?
+template <class T, class... Ts>
+using Contains = absl::disjunction<std::is_same<T, Ts>...>;
+
+template <class From, class To>
+using CopyConst =
+ typename std::conditional<std::is_const<From>::value, const To, To>::type;
+
+// Note: We're not qualifying this with absl:: because it doesn't compile under
+// MSVC.
+template <class T>
+using SliceType = Span<T>;
+
+// This namespace contains no types. It prevents functions defined in it from
+// being found by ADL.
+namespace adl_barrier {
+
+template <class Needle, class... Ts>
+constexpr size_t Find(Needle, Needle, Ts...) {
+ static_assert(!Contains<Needle, Ts...>(), "Duplicate element type");
+ return 0;
+}
+
+template <class Needle, class T, class... Ts>
+constexpr size_t Find(Needle, T, Ts...) {
+ return adl_barrier::Find(Needle(), Ts()...) + 1;
+}
+
+constexpr bool IsPow2(size_t n) { return !(n & (n - 1)); }
+
+// Returns `q * m` for the smallest `q` such that `q * m >= n`.
+// Requires: `m` is a power of two. It's enforced by IsLegalElementType below.
+constexpr size_t Align(size_t n, size_t m) { return (n + m - 1) & ~(m - 1); }
+
+constexpr size_t Min(size_t a, size_t b) { return b < a ? b : a; }
+
+constexpr size_t Max(size_t a) { return a; }
+
+template <class... Ts>
+constexpr size_t Max(size_t a, size_t b, Ts... rest) {
+ return adl_barrier::Max(b < a ? a : b, rest...);
+}
+
+template <class T>
+std::string TypeName() {
+ std::string out;
+ int status = 0;
+ char* demangled = nullptr;
+#ifdef ABSL_INTERNAL_HAS_CXA_DEMANGLE
+ demangled = abi::__cxa_demangle(typeid(T).name(), nullptr, nullptr, &status);
+#endif
+ if (status == 0 && demangled != nullptr) { // Demangling succeeded.
+ absl::StrAppend(&out, "<", demangled, ">");
+ free(demangled);
+ } else {
+#if defined(__GXX_RTTI) || defined(_CPPRTTI)
+ absl::StrAppend(&out, "<", typeid(T).name(), ">");
+#endif
+ }
+ return out;
+}
+
+} // namespace adl_barrier
+
+template <bool C>
+using EnableIf = typename std::enable_if<C, int>::type;
+
+// Can `T` be a template argument of `Layout`?
+template <class T>
+using IsLegalElementType = std::integral_constant<
+ bool, !std::is_reference<T>::value && !std::is_volatile<T>::value &&
+ !std::is_reference<typename Type<T>::type>::value &&
+ !std::is_volatile<typename Type<T>::type>::value &&
+ adl_barrier::IsPow2(AlignOf<T>::value)>;
+
+template <class Elements, class SizeSeq, class OffsetSeq>
+class LayoutImpl;
+
+// Public base class of `Layout` and the result type of `Layout::Partial()`.
+//
+// `Elements...` contains all template arguments of `Layout` that created this
+// instance.
+//
+// `SizeSeq...` is `[0, NumSizes)` where `NumSizes` is the number of arguments
+// passed to `Layout::Partial()` or `Layout::Layout()`.
+//
+// `OffsetSeq...` is `[0, NumOffsets)` where `NumOffsets` is
+// `Min(sizeof...(Elements), NumSizes + 1)` (the number of arrays for which we
+// can compute offsets).
+template <class... Elements, size_t... SizeSeq, size_t... OffsetSeq>
+class LayoutImpl<std::tuple<Elements...>, absl::index_sequence<SizeSeq...>,
+ absl::index_sequence<OffsetSeq...>> {
+ private:
+ static_assert(sizeof...(Elements) > 0, "At least one field is required");
+ static_assert(absl::conjunction<IsLegalElementType<Elements>...>::value,
+ "Invalid element type (see IsLegalElementType)");
+
+ enum {
+ NumTypes = sizeof...(Elements),
+ NumSizes = sizeof...(SizeSeq),
+ NumOffsets = sizeof...(OffsetSeq),
+ };
+
+ // These are guaranteed by `Layout`.
+ static_assert(NumOffsets == adl_barrier::Min(NumTypes, NumSizes + 1),
+ "Internal error");
+ static_assert(NumTypes > 0, "Internal error");
+
+ // Returns the index of `T` in `Elements...`. Results in a compilation error
+ // if `Elements...` doesn't contain exactly one instance of `T`.
+ template <class T>
+ static constexpr size_t ElementIndex() {
+ static_assert(Contains<Type<T>, Type<typename Type<Elements>::type>...>(),
+ "Type not found");
+ return adl_barrier::Find(Type<T>(),
+ Type<typename Type<Elements>::type>()...);
+ }
+
+ template <size_t N>
+ using ElementAlignment =
+ AlignOf<typename std::tuple_element<N, std::tuple<Elements...>>::type>;
+
+ public:
+ // Element types of all arrays packed in a tuple.
+ using ElementTypes = std::tuple<typename Type<Elements>::type...>;
+
+ // Element type of the Nth array.
+ template <size_t N>
+ using ElementType = typename std::tuple_element<N, ElementTypes>::type;
+
+ constexpr explicit LayoutImpl(IntToSize<SizeSeq>... sizes)
+ : size_{sizes...} {}
+
+ // Alignment of the layout, equal to the strictest alignment of all elements.
+ // All pointers passed to the methods of layout must be aligned to this value.
+ static constexpr size_t Alignment() {
+ return adl_barrier::Max(AlignOf<Elements>::value...);
+ }
+
+ // Offset in bytes of the Nth array.
+ //
+ // // int[3], 4 bytes of padding, double[4].
+ // Layout<int, double> x(3, 4);
+ // assert(x.Offset<0>() == 0); // The ints starts from 0.
+ // assert(x.Offset<1>() == 16); // The doubles starts from 16.
+ //
+ // Requires: `N <= NumSizes && N < sizeof...(Ts)`.
+ template <size_t N, EnableIf<N == 0> = 0>
+ constexpr size_t Offset() const {
+ return 0;
+ }
+
+ template <size_t N, EnableIf<N != 0> = 0>
+ constexpr size_t Offset() const {
+ static_assert(N < NumOffsets, "Index out of bounds");
+ return adl_barrier::Align(
+ Offset<N - 1>() + SizeOf<ElementType<N - 1>>() * size_[N - 1],
+ ElementAlignment<N>::value);
+ }
+
+ // Offset in bytes of the array with the specified element type. There must
+ // be exactly one such array and its zero-based index must be at most
+ // `NumSizes`.
+ //
+ // // int[3], 4 bytes of padding, double[4].
+ // Layout<int, double> x(3, 4);
+ // assert(x.Offset<int>() == 0); // The ints starts from 0.
+ // assert(x.Offset<double>() == 16); // The doubles starts from 16.
+ template <class T>
+ constexpr size_t Offset() const {
+ return Offset<ElementIndex<T>()>();
+ }
+
+ // Offsets in bytes of all arrays for which the offsets are known.
+ constexpr std::array<size_t, NumOffsets> Offsets() const {
+ return {{Offset<OffsetSeq>()...}};
+ }
+
+ // The number of elements in the Nth array. This is the Nth argument of
+ // `Layout::Partial()` or `Layout::Layout()` (zero-based).
+ //
+ // // int[3], 4 bytes of padding, double[4].
+ // Layout<int, double> x(3, 4);
+ // assert(x.Size<0>() == 3);
+ // assert(x.Size<1>() == 4);
+ //
+ // Requires: `N < NumSizes`.
+ template <size_t N>
+ constexpr size_t Size() const {
+ static_assert(N < NumSizes, "Index out of bounds");
+ return size_[N];
+ }
+
+ // The number of elements in the array with the specified element type.
+ // There must be exactly one such array and its zero-based index must be
+ // at most `NumSizes`.
+ //
+ // // int[3], 4 bytes of padding, double[4].
+ // Layout<int, double> x(3, 4);
+ // assert(x.Size<int>() == 3);
+ // assert(x.Size<double>() == 4);
+ template <class T>
+ constexpr size_t Size() const {
+ return Size<ElementIndex<T>()>();
+ }
+
+ // The number of elements of all arrays for which they are known.
+ constexpr std::array<size_t, NumSizes> Sizes() const {
+ return {{Size<SizeSeq>()...}};
+ }
+
+ // Pointer to the beginning of the Nth array.
+ //
+ // `Char` must be `[const] [signed|unsigned] char`.
+ //
+ // // int[3], 4 bytes of padding, double[4].
+ // Layout<int, double> x(3, 4);
+ // unsigned char* p = new unsigned char[x.AllocSize()];
+ // int* ints = x.Pointer<0>(p);
+ // double* doubles = x.Pointer<1>(p);
+ //
+ // Requires: `N <= NumSizes && N < sizeof...(Ts)`.
+ // Requires: `p` is aligned to `Alignment()`.
+ template <size_t N, class Char>
+ CopyConst<Char, ElementType<N>>* Pointer(Char* p) const {
+ using C = typename std::remove_const<Char>::type;
+ static_assert(
+ std::is_same<C, char>() || std::is_same<C, unsigned char>() ||
+ std::is_same<C, signed char>(),
+ "The argument must be a pointer to [const] [signed|unsigned] char");
+ constexpr size_t alignment = Alignment();
+ (void)alignment;
+ assert(reinterpret_cast<uintptr_t>(p) % alignment == 0);
+ return reinterpret_cast<CopyConst<Char, ElementType<N>>*>(p + Offset<N>());
+ }
+
+ // Pointer to the beginning of the array with the specified element type.
+ // There must be exactly one such array and its zero-based index must be at
+ // most `NumSizes`.
+ //
+ // `Char` must be `[const] [signed|unsigned] char`.
+ //
+ // // int[3], 4 bytes of padding, double[4].
+ // Layout<int, double> x(3, 4);
+ // unsigned char* p = new unsigned char[x.AllocSize()];
+ // int* ints = x.Pointer<int>(p);
+ // double* doubles = x.Pointer<double>(p);
+ //
+ // Requires: `p` is aligned to `Alignment()`.
+ template <class T, class Char>
+ CopyConst<Char, T>* Pointer(Char* p) const {
+ return Pointer<ElementIndex<T>()>(p);
+ }
+
+ // Pointers to all arrays for which pointers are known.
+ //
+ // `Char` must be `[const] [signed|unsigned] char`.
+ //
+ // // int[3], 4 bytes of padding, double[4].
+ // Layout<int, double> x(3, 4);
+ // unsigned char* p = new unsigned char[x.AllocSize()];
+ //
+ // int* ints;
+ // double* doubles;
+ // std::tie(ints, doubles) = x.Pointers(p);
+ //
+ // Requires: `p` is aligned to `Alignment()`.
+ //
+ // Note: We're not using ElementType alias here because it does not compile
+ // under MSVC.
+ template <class Char>
+ std::tuple<CopyConst<
+ Char, typename std::tuple_element<OffsetSeq, ElementTypes>::type>*...>
+ Pointers(Char* p) const {
+ return std::tuple<CopyConst<Char, ElementType<OffsetSeq>>*...>(
+ Pointer<OffsetSeq>(p)...);
+ }
+
+ // The Nth array.
+ //
+ // `Char` must be `[const] [signed|unsigned] char`.
+ //
+ // // int[3], 4 bytes of padding, double[4].
+ // Layout<int, double> x(3, 4);
+ // unsigned char* p = new unsigned char[x.AllocSize()];
+ // Span<int> ints = x.Slice<0>(p);
+ // Span<double> doubles = x.Slice<1>(p);
+ //
+ // Requires: `N < NumSizes`.
+ // Requires: `p` is aligned to `Alignment()`.
+ template <size_t N, class Char>
+ SliceType<CopyConst<Char, ElementType<N>>> Slice(Char* p) const {
+ return SliceType<CopyConst<Char, ElementType<N>>>(Pointer<N>(p), Size<N>());
+ }
+
+ // The array with the specified element type. There must be exactly one
+ // such array and its zero-based index must be less than `NumSizes`.
+ //
+ // `Char` must be `[const] [signed|unsigned] char`.
+ //
+ // // int[3], 4 bytes of padding, double[4].
+ // Layout<int, double> x(3, 4);
+ // unsigned char* p = new unsigned char[x.AllocSize()];
+ // Span<int> ints = x.Slice<int>(p);
+ // Span<double> doubles = x.Slice<double>(p);
+ //
+ // Requires: `p` is aligned to `Alignment()`.
+ template <class T, class Char>
+ SliceType<CopyConst<Char, T>> Slice(Char* p) const {
+ return Slice<ElementIndex<T>()>(p);
+ }
+
+ // All arrays with known sizes.
+ //
+ // `Char` must be `[const] [signed|unsigned] char`.
+ //
+ // // int[3], 4 bytes of padding, double[4].
+ // Layout<int, double> x(3, 4);
+ // unsigned char* p = new unsigned char[x.AllocSize()];
+ //
+ // Span<int> ints;
+ // Span<double> doubles;
+ // std::tie(ints, doubles) = x.Slices(p);
+ //
+ // Requires: `p` is aligned to `Alignment()`.
+ //
+ // Note: We're not using ElementType alias here because it does not compile
+ // under MSVC.
+ template <class Char>
+ std::tuple<SliceType<CopyConst<
+ Char, typename std::tuple_element<SizeSeq, ElementTypes>::type>>...>
+ Slices(Char* p) const {
+ // Workaround for https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63875 (fixed
+ // in 6.1).
+ (void)p;
+ return std::tuple<SliceType<CopyConst<Char, ElementType<SizeSeq>>>...>(
+ Slice<SizeSeq>(p)...);
+ }
+
+ // The size of the allocation that fits all arrays.
+ //
+ // // int[3], 4 bytes of padding, double[4].
+ // Layout<int, double> x(3, 4);
+ // unsigned char* p = new unsigned char[x.AllocSize()]; // 48 bytes
+ //
+ // Requires: `NumSizes == sizeof...(Ts)`.
+ constexpr size_t AllocSize() const {
+ static_assert(NumTypes == NumSizes, "You must specify sizes of all fields");
+ return Offset<NumTypes - 1>() +
+ SizeOf<ElementType<NumTypes - 1>>() * size_[NumTypes - 1];
+ }
+
+ // If built with --config=asan, poisons padding bytes (if any) in the
+ // allocation. The pointer must point to a memory block at least
+ // `AllocSize()` bytes in length.
+ //
+ // `Char` must be `[const] [signed|unsigned] char`.
+ //
+ // Requires: `p` is aligned to `Alignment()`.
+ template <class Char, size_t N = NumOffsets - 1, EnableIf<N == 0> = 0>
+ void PoisonPadding(const Char* p) const {
+ Pointer<0>(p); // verify the requirements on `Char` and `p`
+ }
+
+ template <class Char, size_t N = NumOffsets - 1, EnableIf<N != 0> = 0>
+ void PoisonPadding(const Char* p) const {
+ static_assert(N < NumOffsets, "Index out of bounds");
+ (void)p;
+#ifdef ADDRESS_SANITIZER
+ PoisonPadding<Char, N - 1>(p);
+ // The `if` is an optimization. It doesn't affect the observable behaviour.
+ if (ElementAlignment<N - 1>::value % ElementAlignment<N>::value) {
+ size_t start =
+ Offset<N - 1>() + SizeOf<ElementType<N - 1>>() * size_[N - 1];
+ ASAN_POISON_MEMORY_REGION(p + start, Offset<N>() - start);
+ }
+#endif
+ }
+
+ // Human-readable description of the memory layout. Useful for debugging.
+ // Slow.
+ //
+ // // char[5], 3 bytes of padding, int[3], 4 bytes of padding, followed
+ // // by an unknown number of doubles.
+ // auto x = Layout<char, int, double>::Partial(5, 3);
+ // assert(x.DebugString() ==
+ // "@0<char>(1)[5]; @8<int>(4)[3]; @24<double>(8)");
+ //
+ // Each field is in the following format: @offset<type>(sizeof)[size] (<type>
+ // may be missing depending on the target platform). For example,
+ // @8<int>(4)[3] means that at offset 8 we have an array of ints, where each
+ // int is 4 bytes, and we have 3 of those ints. The size of the last field may
+ // be missing (as in the example above). Only fields with known offsets are
+ // described. Type names may differ across platforms: one compiler might
+ // produce "unsigned*" where another produces "unsigned int *".
+ std::string DebugString() const {
+ const auto offsets = Offsets();
+ const size_t sizes[] = {SizeOf<ElementType<OffsetSeq>>()...};
+ const std::string types[] = {
+ adl_barrier::TypeName<ElementType<OffsetSeq>>()...};
+ std::string res = absl::StrCat("@0", types[0], "(", sizes[0], ")");
+ for (size_t i = 0; i != NumOffsets - 1; ++i) {
+ absl::StrAppend(&res, "[", size_[i], "]; @", offsets[i + 1], types[i + 1],
+ "(", sizes[i + 1], ")");
+ }
+ // NumSizes is a constant that may be zero. Some compilers cannot see that
+ // inside the if statement "size_[NumSizes - 1]" must be valid.
+ int last = static_cast<int>(NumSizes) - 1;
+ if (NumTypes == NumSizes && last >= 0) {
+ absl::StrAppend(&res, "[", size_[last], "]");
+ }
+ return res;
+ }
+
+ private:
+ // Arguments of `Layout::Partial()` or `Layout::Layout()`.
+ size_t size_[NumSizes > 0 ? NumSizes : 1];
+};
+
+template <size_t NumSizes, class... Ts>
+using LayoutType = LayoutImpl<
+ std::tuple<Ts...>, absl::make_index_sequence<NumSizes>,
+ absl::make_index_sequence<adl_barrier::Min(sizeof...(Ts), NumSizes + 1)>>;
+
+} // namespace internal_layout
+
+// Descriptor of arrays of various types and sizes laid out in memory one after
+// another. See the top of the file for documentation.
+//
+// Check out the public API of internal_layout::LayoutImpl above. The type is
+// internal to the library but its methods are public, and they are inherited
+// by `Layout`.
+template <class... Ts>
+class Layout : public internal_layout::LayoutType<sizeof...(Ts), Ts...> {
+ public:
+ static_assert(sizeof...(Ts) > 0, "At least one field is required");
+ static_assert(
+ absl::conjunction<internal_layout::IsLegalElementType<Ts>...>::value,
+ "Invalid element type (see IsLegalElementType)");
+
+ // The result type of `Partial()` with `NumSizes` arguments.
+ template <size_t NumSizes>
+ using PartialType = internal_layout::LayoutType<NumSizes, Ts...>;
+
+ // `Layout` knows the element types of the arrays we want to lay out in
+ // memory but not the number of elements in each array.
+ // `Partial(size1, ..., sizeN)` allows us to specify the latter. The
+ // resulting immutable object can be used to obtain pointers to the
+ // individual arrays.
+ //
+ // It's allowed to pass fewer array sizes than the number of arrays. E.g.,
+ // if all you need is to the offset of the second array, you only need to
+ // pass one argument -- the number of elements in the first array.
+ //
+ // // int[3] followed by 4 bytes of padding and an unknown number of
+ // // doubles.
+ // auto x = Layout<int, double>::Partial(3);
+ // // doubles start at byte 16.
+ // assert(x.Offset<1>() == 16);
+ //
+ // If you know the number of elements in all arrays, you can still call
+ // `Partial()` but it's more convenient to use the constructor of `Layout`.
+ //
+ // Layout<int, double> x(3, 5);
+ //
+ // Note: The sizes of the arrays must be specified in number of elements,
+ // not in bytes.
+ //
+ // Requires: `sizeof...(Sizes) <= sizeof...(Ts)`.
+ // Requires: all arguments are convertible to `size_t`.
+ template <class... Sizes>
+ static constexpr PartialType<sizeof...(Sizes)> Partial(Sizes&&... sizes) {
+ static_assert(sizeof...(Sizes) <= sizeof...(Ts), "");
+ return PartialType<sizeof...(Sizes)>(absl::forward<Sizes>(sizes)...);
+ }
+
+ // Creates a layout with the sizes of all arrays specified. If you know
+ // only the sizes of the first N arrays (where N can be zero), you can use
+ // `Partial()` defined above. The constructor is essentially equivalent to
+ // calling `Partial()` and passing in all array sizes; the constructor is
+ // provided as a convenient abbreviation.
+ //
+ // Note: The sizes of the arrays must be specified in number of elements,
+ // not in bytes.
+ constexpr explicit Layout(internal_layout::TypeToSize<Ts>... sizes)
+ : internal_layout::LayoutType<sizeof...(Ts), Ts...>(sizes...) {}
+};
+
+} // namespace container_internal
+} // namespace absl
+
+#endif // ABSL_CONTAINER_INTERNAL_LAYOUT_H_
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