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| // 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////      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.//// An open-addressing// hashtable with quadratic probing.//// This is a low level hashtable on top of which different interfaces can be// implemented, like flat_hash_set, node_hash_set, string_hash_set, etc.//// The table interface is similar to that of std::unordered_set. Notable// differences are that most member functions support heterogeneous keys when// BOTH the hash and eq functions are marked as transparent. They do so by// providing a typedef called `is_transparent`.//// When heterogeneous lookup is enabled, functions that take key_type act as if// they have an overload set like:////   iterator find(const key_type& key);//   template <class K>//   iterator find(const K& key);////   size_type erase(const key_type& key);//   template <class K>//   size_type erase(const K& key);////   std::pair<iterator, iterator> equal_range(const key_type& key);//   template <class K>//   std::pair<iterator, iterator> equal_range(const K& key);//// When heterogeneous lookup is disabled, only the explicit `key_type` overloads// exist.//// find() also supports passing the hash explicitly:////   iterator find(const key_type& key, size_t hash);//   template <class U>//   iterator find(const U& key, size_t hash);//// In addition the pointer to element and iterator stability guarantees are// weaker: all iterators and pointers are invalidated after a new element is// inserted.//// IMPLEMENTATION DETAILS//// The table stores elements inline in a slot array. In addition to the slot// array the table maintains some control state per slot. The extra state is one// byte per slot and stores empty or deleted marks, or alternatively 7 bits from// the hash of an occupied slot. The table is split into logical groups of// slots, like so:////      Group 1         Group 2        Group 3// +---------------+---------------+---------------+// | | | | | | | | | | | | | | | | | | | | | | | | |// +---------------+---------------+---------------+//// On lookup the hash is split into two parts:// - H2: 7 bits (those stored in the control bytes)// - H1: the rest of the bits// The groups are probed using H1. For each group the slots are matched to H2 in// parallel. Because H2 is 7 bits (128 states) and the number of slots per group// is low (8 or 16) in almost all cases a match in H2 is also a lookup hit.//// On insert, once the right group is found (as in lookup), its slots are// filled in order.//// On erase a slot is cleared. In case the group did not have any empty slots// before the erase, the erased slot is marked as deleted.//// Groups without empty slots (but maybe with deleted slots) extend the probe// sequence. The probing algorithm is quadratic. Given N the number of groups,// the probing function for the i'th probe is:////   P(0) = H1 % N////   P(i) = (P(i - 1) + i) % N//// This probing function guarantees that after N probes, all the groups of the// table will be probed exactly once.#ifndef ABSL_CONTAINER_INTERNAL_RAW_HASH_SET_H_#define ABSL_CONTAINER_INTERNAL_RAW_HASH_SET_H_#include <algorithm>#include <cmath>#include <cstdint>#include <cstring>#include <iterator>#include <limits>#include <memory>#include <tuple>#include <type_traits>#include <utility>#include "absl/base/internal/bits.h"#include "absl/base/internal/endian.h"#include "absl/base/port.h"#include "absl/container/internal/common.h"#include "absl/container/internal/compressed_tuple.h"#include "absl/container/internal/container_memory.h"#include "absl/container/internal/hash_policy_traits.h"#include "absl/container/internal/hashtable_debug_hooks.h"#include "absl/container/internal/hashtablez_sampler.h"#include "absl/container/internal/have_sse.h"#include "absl/container/internal/layout.h"#include "absl/memory/memory.h"#include "absl/meta/type_traits.h"#include "absl/types/optional.h"#include "absl/utility/utility.h"namespace absl {namespace container_internal {template <size_t Width>class probe_seq { public:  probe_seq(size_t hash, size_t mask) {    assert(((mask + 1) & mask) == 0 && "not a mask");    mask_ = mask;    offset_ = hash & mask_;  }  size_t offset() const { return offset_; }  size_t offset(size_t i) const { return (offset_ + i) & mask_; }  void next() {    index_ += Width;    offset_ += index_;    offset_ &= mask_;  }  // 0-based probe index. The i-th probe in the probe sequence.  size_t index() const { return index_; } private:  size_t mask_;  size_t offset_;  size_t index_ = 0;};template <class ContainerKey, class Hash, class Eq>struct RequireUsableKey {  template <class PassedKey, class... Args>  std::pair<      decltype(std::declval<const Hash&>()(std::declval<const PassedKey&>())),      decltype(std::declval<const Eq&>()(std::declval<const ContainerKey&>(),                                         std::declval<const PassedKey&>()))>*  operator()(const PassedKey&, const Args&...) const;};template <class E, class Policy, class Hash, class Eq, class... Ts>struct IsDecomposable : std::false_type {};template <class Policy, class Hash, class Eq, class... Ts>struct IsDecomposable<    absl::void_t<decltype(        Policy::apply(RequireUsableKey<typename Policy::key_type, Hash, Eq>(),                      std::declval<Ts>()...))>,    Policy, Hash, Eq, Ts...> : std::true_type {};// TODO(alkis): Switch to std::is_nothrow_swappable when gcc/clang supports it.template <class T>constexpr bool IsNoThrowSwappable() {  using std::swap;  return noexcept(swap(std::declval<T&>(), std::declval<T&>()));}template <typename T>int TrailingZeros(T x) {  return sizeof(T) == 8 ? base_internal::CountTrailingZerosNonZero64(                              static_cast<uint64_t>(x))                        : base_internal::CountTrailingZerosNonZero32(                              static_cast<uint32_t>(x));}template <typename T>int LeadingZeros(T x) {  return sizeof(T) == 8             ? base_internal::CountLeadingZeros64(static_cast<uint64_t>(x))             : base_internal::CountLeadingZeros32(static_cast<uint32_t>(x));}// An abstraction over a bitmask. It provides an easy way to iterate through the// indexes of the set bits of a bitmask.  When Shift=0 (platforms with SSE),// this is a true bitmask.  On non-SSE, platforms the arithematic used to// emulate the SSE behavior works in bytes (Shift=3) and leaves each bytes as// either 0x00 or 0x80.//// For example://   for (int i : BitMask<uint32_t, 16>(0x5)) -> yields 0, 2//   for (int i : BitMask<uint64_t, 8, 3>(0x0000000080800000)) -> yields 2, 3template <class T, int SignificantBits, int Shift = 0>class BitMask {  static_assert(std::is_unsigned<T>::value, "");  static_assert(Shift == 0 || Shift == 3, ""); public:  // These are useful for unit tests (gunit).  using value_type = int;  using iterator = BitMask;  using const_iterator = BitMask;  explicit BitMask(T mask) : mask_(mask) {}  BitMask& operator++() {    mask_ &= (mask_ - 1);    return *this;  }  explicit operator bool() const { return mask_ != 0; }  int operator*() const { return LowestBitSet(); }  int LowestBitSet() const {    return container_internal::TrailingZeros(mask_) >> Shift;  }  int HighestBitSet() const {    return (sizeof(T) * CHAR_BIT - container_internal::LeadingZeros(mask_) -            1) >>           Shift;  }  BitMask begin() const { return *this; }  BitMask end() const { return BitMask(0); }  int TrailingZeros() const {    return container_internal::TrailingZeros(mask_) >> Shift;  }  int LeadingZeros() const {    constexpr int total_significant_bits = SignificantBits << Shift;    constexpr int extra_bits = sizeof(T) * 8 - total_significant_bits;    return container_internal::LeadingZeros(mask_ << extra_bits) >> Shift;  } private:  friend bool operator==(const BitMask& a, const BitMask& b) {    return a.mask_ == b.mask_;  }  friend bool operator!=(const BitMask& a, const BitMask& b) {    return a.mask_ != b.mask_;  }  T mask_;};using ctrl_t = signed char;using h2_t = uint8_t;// The values here are selected for maximum performance. See the static asserts// below for details.enum Ctrl : ctrl_t {  kEmpty = -128,   // 0b10000000  kDeleted = -2,   // 0b11111110  kSentinel = -1,  // 0b11111111};static_assert(    kEmpty & kDeleted & kSentinel & 0x80,    "Special markers need to have the MSB to make checking for them efficient");static_assert(kEmpty < kSentinel && kDeleted < kSentinel,              "kEmpty and kDeleted must be smaller than kSentinel to make the "              "SIMD test of IsEmptyOrDeleted() efficient");static_assert(kSentinel == -1,              "kSentinel must be -1 to elide loading it from memory into SIMD "              "registers (pcmpeqd xmm, xmm)");static_assert(kEmpty == -128,              "kEmpty must be -128 to make the SIMD check for its "              "existence efficient (psignb xmm, xmm)");static_assert(~kEmpty & ~kDeleted & kSentinel & 0x7F,              "kEmpty and kDeleted must share an unset bit that is not shared "              "by kSentinel to make the scalar test for MatchEmptyOrDeleted() "              "efficient");static_assert(kDeleted == -2,              "kDeleted must be -2 to make the implementation of "              "ConvertSpecialToEmptyAndFullToDeleted efficient");// A single block of empty control bytes for tables without any slots allocated.// This enables removing a branch in the hot path of find().inline ctrl_t* EmptyGroup() {  alignas(16) static constexpr ctrl_t empty_group[] = {      kSentinel, kEmpty, kEmpty, kEmpty, kEmpty, kEmpty, kEmpty, kEmpty,      kEmpty,    kEmpty, kEmpty, kEmpty, kEmpty, kEmpty, kEmpty, kEmpty};  return const_cast<ctrl_t*>(empty_group);}// Mixes a randomly generated per-process seed with `hash` and `ctrl` to// randomize insertion order within groups.bool ShouldInsertBackwards(size_t hash, ctrl_t* ctrl);// Returns a hash seed.//// The seed consists of the ctrl_ pointer, which adds enough entropy to ensure// non-determinism of iteration order in most cases.inline size_t HashSeed(const ctrl_t* ctrl) {  // The low bits of the pointer have little or no entropy because of  // alignment. We shift the pointer to try to use higher entropy bits. A  // good number seems to be 12 bits, because that aligns with page size.  return reinterpret_cast<uintptr_t>(ctrl) >> 12;}inline size_t H1(size_t hash, const ctrl_t* ctrl) {  return (hash >> 7) ^ HashSeed(ctrl);}inline ctrl_t H2(size_t hash) { return hash & 0x7F; }inline bool IsEmpty(ctrl_t c) { return c == kEmpty; }inline bool IsFull(ctrl_t c) { return c >= 0; }inline bool IsDeleted(ctrl_t c) { return c == kDeleted; }inline bool IsEmptyOrDeleted(ctrl_t c) { return c < kSentinel; }#if SWISSTABLE_HAVE_SSE2// https://github.com/abseil/abseil-cpp/issues/209// https://gcc.gnu.org/bugzilla/show_bug.cgi?id=87853// _mm_cmpgt_epi8 is broken under GCC with -funsigned-char// Work around this by using the portable implementation of Group// when using -funsigned-char under GCC.inline __m128i _mm_cmpgt_epi8_fixed(__m128i a, __m128i b) {#if defined(__GNUC__) && !defined(__clang__)  if (std::is_unsigned<char>::value) {    const __m128i mask = _mm_set1_epi8(0x80);    const __m128i diff = _mm_subs_epi8(b, a);    return _mm_cmpeq_epi8(_mm_and_si128(diff, mask), mask);  }#endif  return _mm_cmpgt_epi8(a, b);}struct GroupSse2Impl {  static constexpr size_t kWidth = 16;  // the number of slots per group  explicit GroupSse2Impl(const ctrl_t* pos) {    ctrl = _mm_loadu_si128(reinterpret_cast<const __m128i*>(pos));  }  // Returns a bitmask representing the positions of slots that match hash.  BitMask<uint32_t, kWidth> Match(h2_t hash) const {    auto match = _mm_set1_epi8(hash);    return BitMask<uint32_t, kWidth>(        _mm_movemask_epi8(_mm_cmpeq_epi8(match, ctrl)));  }  // Returns a bitmask representing the positions of empty slots.  BitMask<uint32_t, kWidth> MatchEmpty() const {#if SWISSTABLE_HAVE_SSSE3    // This only works because kEmpty is -128.    return BitMask<uint32_t, kWidth>(        _mm_movemask_epi8(_mm_sign_epi8(ctrl, ctrl)));#else    return Match(kEmpty);#endif  }  // Returns a bitmask representing the positions of empty or deleted slots.  BitMask<uint32_t, kWidth> MatchEmptyOrDeleted() const {    auto special = _mm_set1_epi8(kSentinel);    return BitMask<uint32_t, kWidth>(        _mm_movemask_epi8(_mm_cmpgt_epi8_fixed(special, ctrl)));  }  // Returns the number of trailing empty or deleted elements in the group.  uint32_t CountLeadingEmptyOrDeleted() const {    auto special = _mm_set1_epi8(kSentinel);    return TrailingZeros(        _mm_movemask_epi8(_mm_cmpgt_epi8_fixed(special, ctrl)) + 1);  }  void ConvertSpecialToEmptyAndFullToDeleted(ctrl_t* dst) const {    auto msbs = _mm_set1_epi8(static_cast<char>(-128));    auto x126 = _mm_set1_epi8(126);#if SWISSTABLE_HAVE_SSSE3    auto res = _mm_or_si128(_mm_shuffle_epi8(x126, ctrl), msbs);#else    auto zero = _mm_setzero_si128();    auto special_mask = _mm_cmpgt_epi8_fixed(zero, ctrl);    auto res = _mm_or_si128(msbs, _mm_andnot_si128(special_mask, x126));#endif    _mm_storeu_si128(reinterpret_cast<__m128i*>(dst), res);  }  __m128i ctrl;};#endif  // SWISSTABLE_HAVE_SSE2struct GroupPortableImpl {  static constexpr size_t kWidth = 8;  explicit GroupPortableImpl(const ctrl_t* pos)      : ctrl(little_endian::Load64(pos)) {}  BitMask<uint64_t, kWidth, 3> Match(h2_t hash) const {    // For the technique, see:    // http://graphics.stanford.edu/~seander/bithacks.html##ValueInWord    // (Determine if a word has a byte equal to n).    //    // Caveat: there are false positives but:    // - they only occur if there is a real match    // - they never occur on kEmpty, kDeleted, kSentinel    // - they will be handled gracefully by subsequent checks in code    //    // Example:    //   v = 0x1716151413121110    //   hash = 0x12    //   retval = (v - lsbs) & ~v & msbs = 0x0000000080800000    constexpr uint64_t msbs = 0x8080808080808080ULL;    constexpr uint64_t lsbs = 0x0101010101010101ULL;    auto x = ctrl ^ (lsbs * hash);    return BitMask<uint64_t, kWidth, 3>((x - lsbs) & ~x & msbs);  }  BitMask<uint64_t, kWidth, 3> MatchEmpty() const {    constexpr uint64_t msbs = 0x8080808080808080ULL;    return BitMask<uint64_t, kWidth, 3>((ctrl & (~ctrl << 6)) & msbs);  }  BitMask<uint64_t, kWidth, 3> MatchEmptyOrDeleted() const {    constexpr uint64_t msbs = 0x8080808080808080ULL;    return BitMask<uint64_t, kWidth, 3>((ctrl & (~ctrl << 7)) & msbs);  }  uint32_t CountLeadingEmptyOrDeleted() const {    constexpr uint64_t gaps = 0x00FEFEFEFEFEFEFEULL;    return (TrailingZeros(((~ctrl & (ctrl >> 7)) | gaps) + 1) + 7) >> 3;  }  void ConvertSpecialToEmptyAndFullToDeleted(ctrl_t* dst) const {    constexpr uint64_t msbs = 0x8080808080808080ULL;    constexpr uint64_t lsbs = 0x0101010101010101ULL;    auto x = ctrl & msbs;    auto res = (~x + (x >> 7)) & ~lsbs;    little_endian::Store64(dst, res);  }  uint64_t ctrl;};#if SWISSTABLE_HAVE_SSE2using Group = GroupSse2Impl;#elseusing Group = GroupPortableImpl;#endiftemplate <class Policy, class Hash, class Eq, class Alloc>class raw_hash_set;inline bool IsValidCapacity(size_t n) {  return ((n + 1) & n) == 0 && n >= Group::kWidth - 1;}// PRECONDITION://   IsValidCapacity(capacity)//   ctrl[capacity] == kSentinel//   ctrl[i] != kSentinel for all i < capacity// Applies mapping for every byte in ctrl://   DELETED -> EMPTY//   EMPTY -> EMPTY//   FULL -> DELETEDinline void ConvertDeletedToEmptyAndFullToDeleted(    ctrl_t* ctrl, size_t capacity) {  assert(ctrl[capacity] == kSentinel);  assert(IsValidCapacity(capacity));  for (ctrl_t* pos = ctrl; pos != ctrl + capacity + 1; pos += Group::kWidth) {    Group{pos}.ConvertSpecialToEmptyAndFullToDeleted(pos);  }  // Copy the cloned ctrl bytes.  std::memcpy(ctrl + capacity + 1, ctrl, Group::kWidth);  ctrl[capacity] = kSentinel;}// Rounds up the capacity to the next power of 2 minus 1 and ensures it is// greater or equal to Group::kWidth - 1.inline size_t NormalizeCapacity(size_t n) {  constexpr size_t kMinCapacity = Group::kWidth - 1;  return n <= kMinCapacity             ? kMinCapacity             : (std::numeric_limits<size_t>::max)() >> LeadingZeros(n);}// We use 7/8th as maximum load factor.// For 16-wide groups, that gives an average of two empty slots per group.inline size_t CapacityToGrowth(size_t capacity) {  assert(IsValidCapacity(capacity));  // `capacity*7/8`  if (Group::kWidth == 8 && capacity == 7) {    // x-x/8 does not work when x==7.    return 6;  }  return capacity - capacity / 8;}// From desired "growth" to a lowerbound of the necessary capacity.// Might not be a valid one and required NormalizeCapacity().inline size_t GrowthToLowerboundCapacity(size_t growth) {  // `growth*8/7`  if (Group::kWidth == 8 && growth == 7) {    // x+(x-1)/7 does not work when x==7.    return 8;  }  return growth + static_cast<size_t>((static_cast<int64_t>(growth) - 1) / 7);}// The node_handle concept from C++17.// We specialize node_handle for sets and maps. node_handle_base holds the// common API of both.template <typename Policy, typename Alloc>class node_handle_base { protected:  using PolicyTraits = hash_policy_traits<Policy>;  using slot_type = typename PolicyTraits::slot_type; public:  using allocator_type = Alloc;  constexpr node_handle_base() {}  node_handle_base(node_handle_base&& other) noexcept {    *this = std::move(other);  }  ~node_handle_base() { destroy(); }  node_handle_base& operator=(node_handle_base&& other) {    destroy();    if (!other.empty()) {      alloc_ = other.alloc_;      PolicyTraits::transfer(alloc(), slot(), other.slot());      other.reset();    }    return *this;  }  bool empty() const noexcept { return !alloc_; }  explicit operator bool() const noexcept { return !empty(); }  allocator_type get_allocator() const { return *alloc_; } protected:  template <typename, typename, typename, typename>  friend class raw_hash_set;  node_handle_base(const allocator_type& a, slot_type* s) : alloc_(a) {    PolicyTraits::transfer(alloc(), slot(), s);  }  void destroy() {    if (!empty()) {      PolicyTraits::destroy(alloc(), slot());      reset();    }  }  void reset() {    assert(alloc_.has_value());    alloc_ = absl::nullopt;  }  slot_type* slot() const {    assert(!empty());    return reinterpret_cast<slot_type*>(std::addressof(slot_space_));  }  allocator_type* alloc() { return std::addressof(*alloc_); } private:  absl::optional<allocator_type> alloc_;  mutable absl::aligned_storage_t<sizeof(slot_type), alignof(slot_type)>      slot_space_;};// For sets.template <typename Policy, typename Alloc, typename = void>class node_handle : public node_handle_base<Policy, Alloc> {  using Base = typename node_handle::node_handle_base; public:  using value_type = typename Base::PolicyTraits::value_type;  constexpr node_handle() {}  value_type& value() const {    return Base::PolicyTraits::element(this->slot());  } private:  template <typename, typename, typename, typename>  friend class raw_hash_set;  node_handle(const Alloc& a, typename Base::slot_type* s) : Base(a, s) {}};// For maps.template <typename Policy, typename Alloc>class node_handle<Policy, Alloc, absl::void_t<typename Policy::mapped_type>>    : public node_handle_base<Policy, Alloc> {  using Base = typename node_handle::node_handle_base; public:  using key_type = typename Policy::key_type;  using mapped_type = typename Policy::mapped_type;  constexpr node_handle() {}  auto key() const -> decltype(Base::PolicyTraits::key(this->slot())) {    return Base::PolicyTraits::key(this->slot());  }  mapped_type& mapped() const {    return Base::PolicyTraits::value(        &Base::PolicyTraits::element(this->slot()));  } private:  template <typename, typename, typename, typename>  friend class raw_hash_set;  node_handle(const Alloc& a, typename Base::slot_type* s) : Base(a, s) {}};// Implement the insert_return_type<> concept of C++17.template <class Iterator, class NodeType>struct insert_return_type {  Iterator position;  bool inserted;  NodeType node;};// Policy: a policy defines how to perform different operations on// the slots of the hashtable (see hash_policy_traits.h for the full interface// of policy).//// Hash: a (possibly polymorphic) functor that hashes keys of the hashtable. The// functor should accept a key and return size_t as hash. For best performance// it is important that the hash function provides high entropy across all bits// of the hash.//// Eq: a (possibly polymorphic) functor that compares two keys for equality. It// should accept two (of possibly different type) keys and return a bool: true// if they are equal, false if they are not. If two keys compare equal, then// their hash values as defined by Hash MUST be equal.//// Allocator: an Allocator [http://devdocs.io/cpp/concept/allocator] with which// the storage of the hashtable will be allocated and the elements will be// constructed and destroyed.template <class Policy, class Hash, class Eq, class Alloc>class raw_hash_set {  using PolicyTraits = hash_policy_traits<Policy>;  using KeyArgImpl =      KeyArg<IsTransparent<Eq>::value && IsTransparent<Hash>::value>; public:  using init_type = typename PolicyTraits::init_type;  using key_type = typename PolicyTraits::key_type;  // TODO(sbenza): Hide slot_type as it is an implementation detail. Needs user  // code fixes!  using slot_type = typename PolicyTraits::slot_type;  using allocator_type = Alloc;  using size_type = size_t;  using difference_type = ptrdiff_t;  using hasher = Hash;  using key_equal = Eq;  using policy_type = Policy;  using value_type = typename PolicyTraits::value_type;  using reference = value_type&;  using const_reference = const value_type&;  using pointer = typename absl::allocator_traits<      allocator_type>::template rebind_traits<value_type>::pointer;  using const_pointer = typename absl::allocator_traits<      allocator_type>::template rebind_traits<value_type>::const_pointer;  // Alias used for heterogeneous lookup functions.  // `key_arg<K>` evaluates to `K` when the functors are transparent and to  // `key_type` otherwise. It permits template argument deduction on `K` for the  // transparent case.  template <class K>  using key_arg = typename KeyArgImpl::template type<K, key_type>; private:  // Give an early error when key_type is not hashable/eq.  auto KeyTypeCanBeHashed(const Hash& h, const key_type& k) -> decltype(h(k));  auto KeyTypeCanBeEq(const Eq& eq, const key_type& k) -> decltype(eq(k, k));  using Layout = absl::container_internal::Layout<ctrl_t, slot_type>;  static Layout MakeLayout(size_t capacity) {    assert(IsValidCapacity(capacity));    return Layout(capacity + Group::kWidth + 1, capacity);  }  using AllocTraits = absl::allocator_traits<allocator_type>;  using SlotAlloc = typename absl::allocator_traits<      allocator_type>::template rebind_alloc<slot_type>;  using SlotAllocTraits = typename absl::allocator_traits<      allocator_type>::template rebind_traits<slot_type>;  static_assert(std::is_lvalue_reference<reference>::value,                "Policy::element() must return a reference");  template <typename T>  struct SameAsElementReference      : std::is_same<typename std::remove_cv<                         typename std::remove_reference<reference>::type>::type,                     typename std::remove_cv<                         typename std::remove_reference<T>::type>::type> {};  // An enabler for insert(T&&): T must be convertible to init_type or be the  // same as [cv] value_type [ref].  // Note: we separate SameAsElementReference into its own type to avoid using  // reference unless we need to. MSVC doesn't seem to like it in some  // cases.  template <class T>  using RequiresInsertable = typename std::enable_if<      absl::disjunction<std::is_convertible<T, init_type>,                        SameAsElementReference<T>>::value,      int>::type;  // RequiresNotInit is a workaround for gcc prior to 7.1.  // See https://godbolt.org/g/Y4xsUh.  template <class T>  using RequiresNotInit =      typename std::enable_if<!std::is_same<T, init_type>::value, int>::type;  template <class... Ts>  using IsDecomposable = IsDecomposable<void, PolicyTraits, Hash, Eq, Ts...>; public:  static_assert(std::is_same<pointer, value_type*>::value,                "Allocators with custom pointer types are not supported");  static_assert(std::is_same<const_pointer, const value_type*>::value,                "Allocators with custom pointer types are not supported");  class iterator {    friend class raw_hash_set;   public:    using iterator_category = std::forward_iterator_tag;    using value_type = typename raw_hash_set::value_type;    using reference =        absl::conditional_t<PolicyTraits::constant_iterators::value,                            const value_type&, value_type&>;    using pointer = absl::remove_reference_t<reference>*;    using difference_type = typename raw_hash_set::difference_type;    iterator() {}    // PRECONDITION: not an end() iterator.    reference operator*() const { return PolicyTraits::element(slot_); }    // PRECONDITION: not an end() iterator.    pointer operator->() const { return &operator*(); }    // PRECONDITION: not an end() iterator.    iterator& operator++() {      ++ctrl_;      ++slot_;      skip_empty_or_deleted();      return *this;    }    // PRECONDITION: not an end() iterator.    iterator operator++(int) {      auto tmp = *this;      ++*this;      return tmp;    }    friend bool operator==(const iterator& a, const iterator& b) {      return a.ctrl_ == b.ctrl_;    }    friend bool operator!=(const iterator& a, const iterator& b) {      return !(a == b);    }   private:    iterator(ctrl_t* ctrl) : ctrl_(ctrl) {}  // for end()    iterator(ctrl_t* ctrl, slot_type* slot) : ctrl_(ctrl), slot_(slot) {}    void skip_empty_or_deleted() {      while (IsEmptyOrDeleted(*ctrl_)) {        // ctrl is not necessarily aligned to Group::kWidth. It is also likely        // to read past the space for ctrl bytes and into slots. This is ok        // because ctrl has sizeof() == 1 and slot has sizeof() >= 1 so there        // is no way to read outside the combined slot array.        uint32_t shift = Group{ctrl_}.CountLeadingEmptyOrDeleted();        ctrl_ += shift;        slot_ += shift;      }    }    ctrl_t* ctrl_ = nullptr;    // To avoid uninitialized member warnigs, put slot_ in an anonymous union.    // The member is not initialized on singleton and end iterators.    union {      slot_type* slot_;    };  };  class const_iterator {    friend class raw_hash_set;   public:    using iterator_category = typename iterator::iterator_category;    using value_type = typename raw_hash_set::value_type;    using reference = typename raw_hash_set::const_reference;    using pointer = typename raw_hash_set::const_pointer;    using difference_type = typename raw_hash_set::difference_type;    const_iterator() {}    // Implicit construction from iterator.    const_iterator(iterator i) : inner_(std::move(i)) {}    reference operator*() const { return *inner_; }    pointer operator->() const { return inner_.operator->(); }    const_iterator& operator++() {      ++inner_;      return *this;    }    const_iterator operator++(int) { return inner_++; }    friend bool operator==(const const_iterator& a, const const_iterator& b) {      return a.inner_ == b.inner_;    }    friend bool operator!=(const const_iterator& a, const const_iterator& b) {      return !(a == b);    }   private:    const_iterator(const ctrl_t* ctrl, const slot_type* slot)        : inner_(const_cast<ctrl_t*>(ctrl), const_cast<slot_type*>(slot)) {}    iterator inner_;  };  using node_type = container_internal::node_handle<Policy, Alloc>;  raw_hash_set() noexcept(      std::is_nothrow_default_constructible<hasher>::value&&          std::is_nothrow_default_constructible<key_equal>::value&&              std::is_nothrow_default_constructible<allocator_type>::value) {}  explicit raw_hash_set(size_t bucket_count, const hasher& hash = hasher(),                        const key_equal& eq = key_equal(),                        const allocator_type& alloc = allocator_type())      : ctrl_(EmptyGroup()), settings_(0, hash, eq, alloc) {    if (bucket_count) {      capacity_ = NormalizeCapacity(bucket_count);      reset_growth_left();      initialize_slots();    }  }  raw_hash_set(size_t bucket_count, const hasher& hash,               const allocator_type& alloc)      : raw_hash_set(bucket_count, hash, key_equal(), alloc) {}  raw_hash_set(size_t bucket_count, const allocator_type& alloc)      : raw_hash_set(bucket_count, hasher(), key_equal(), alloc) {}  explicit raw_hash_set(const allocator_type& alloc)      : raw_hash_set(0, hasher(), key_equal(), alloc) {}  template <class InputIter>  raw_hash_set(InputIter first, InputIter last, size_t bucket_count = 0,               const hasher& hash = hasher(), const key_equal& eq = key_equal(),               const allocator_type& alloc = allocator_type())      : raw_hash_set(bucket_count, hash, eq, alloc) {    insert(first, last);  }  template <class InputIter>  raw_hash_set(InputIter first, InputIter last, size_t bucket_count,               const hasher& hash, const allocator_type& alloc)      : raw_hash_set(first, last, bucket_count, hash, key_equal(), alloc) {}  template <class InputIter>  raw_hash_set(InputIter first, InputIter last, size_t bucket_count,               const allocator_type& alloc)      : raw_hash_set(first, last, bucket_count, hasher(), key_equal(), alloc) {}  template <class InputIter>  raw_hash_set(InputIter first, InputIter last, const allocator_type& alloc)      : raw_hash_set(first, last, 0, hasher(), key_equal(), alloc) {}  // Instead of accepting std::initializer_list<value_type> as the first  // argument like std::unordered_set<value_type> does, we have two overloads  // that accept std::initializer_list<T> and std::initializer_list<init_type>.  // This is advantageous for performance.  //  //   // Turns {"abc", "def"} into std::initializer_list<std::string>, then copies  //   // the strings into the set.  //   std::unordered_set<std::string> s = {"abc", "def"};  //  //   // Turns {"abc", "def"} into std::initializer_list<const char*>, then  //   // copies the strings into the set.  //   absl::flat_hash_set<std::string> s = {"abc", "def"};  //  // The same trick is used in insert().  //  // The enabler is necessary to prevent this constructor from triggering where  // the copy constructor is meant to be called.  //  //   absl::flat_hash_set<int> a, b{a};  //  // RequiresNotInit<T> is a workaround for gcc prior to 7.1.  template <class T, RequiresNotInit<T> = 0, RequiresInsertable<T> = 0>  raw_hash_set(std::initializer_list<T> init, size_t bucket_count = 0,               const hasher& hash = hasher(), const key_equal& eq = key_equal(),               const allocator_type& alloc = allocator_type())      : raw_hash_set(init.begin(), init.end(), bucket_count, hash, eq, alloc) {}  raw_hash_set(std::initializer_list<init_type> init, size_t bucket_count = 0,               const hasher& hash = hasher(), const key_equal& eq = key_equal(),               const allocator_type& alloc = allocator_type())      : raw_hash_set(init.begin(), init.end(), bucket_count, hash, eq, alloc) {}  template <class T, RequiresNotInit<T> = 0, RequiresInsertable<T> = 0>  raw_hash_set(std::initializer_list<T> init, size_t bucket_count,               const hasher& hash, const allocator_type& alloc)      : raw_hash_set(init, bucket_count, hash, key_equal(), alloc) {}  raw_hash_set(std::initializer_list<init_type> init, size_t bucket_count,               const hasher& hash, const allocator_type& alloc)      : raw_hash_set(init, bucket_count, hash, key_equal(), alloc) {}  template <class T, RequiresNotInit<T> = 0, RequiresInsertable<T> = 0>  raw_hash_set(std::initializer_list<T> init, size_t bucket_count,               const allocator_type& alloc)      : raw_hash_set(init, bucket_count, hasher(), key_equal(), alloc) {}  raw_hash_set(std::initializer_list<init_type> init, size_t bucket_count,               const allocator_type& alloc)      : raw_hash_set(init, bucket_count, hasher(), key_equal(), alloc) {}  template <class T, RequiresNotInit<T> = 0, RequiresInsertable<T> = 0>  raw_hash_set(std::initializer_list<T> init, const allocator_type& alloc)      : raw_hash_set(init, 0, hasher(), key_equal(), alloc) {}  raw_hash_set(std::initializer_list<init_type> init,               const allocator_type& alloc)      : raw_hash_set(init, 0, hasher(), key_equal(), alloc) {}  raw_hash_set(const raw_hash_set& that)      : raw_hash_set(that, AllocTraits::select_on_container_copy_construction(                               that.alloc_ref())) {}  raw_hash_set(const raw_hash_set& that, const allocator_type& a)      : raw_hash_set(0, that.hash_ref(), that.eq_ref(), a) {    reserve(that.size());    // Because the table is guaranteed to be empty, we can do something faster    // than a full `insert`.    for (const auto& v : that) {      const size_t hash = PolicyTraits::apply(HashElement{hash_ref()}, v);      auto target = find_first_non_full(hash);      set_ctrl(target.offset, H2(hash));      emplace_at(target.offset, v);      infoz_.RecordInsert(hash, target.probe_length);    }    size_ = that.size();    growth_left() -= that.size();  }  raw_hash_set(raw_hash_set&& that) noexcept(      std::is_nothrow_copy_constructible<hasher>::value&&          std::is_nothrow_copy_constructible<key_equal>::value&&              std::is_nothrow_copy_constructible<allocator_type>::value)      : ctrl_(absl::exchange(that.ctrl_, EmptyGroup())),        slots_(absl::exchange(that.slots_, nullptr)),        size_(absl::exchange(that.size_, 0)),        capacity_(absl::exchange(that.capacity_, 0)),        infoz_(absl::exchange(that.infoz_, HashtablezInfoHandle())),        // Hash, equality and allocator are copied instead of moved because        // `that` must be left valid. If Hash is std::function<Key>, moving it        // would create a nullptr functor that cannot be called.        settings_(that.settings_) {    // growth_left was copied above, reset the one from `that`.    that.growth_left() = 0;  }  raw_hash_set(raw_hash_set&& that, const allocator_type& a)      : ctrl_(EmptyGroup()),        slots_(nullptr),        size_(0),        capacity_(0),        settings_(0, that.hash_ref(), that.eq_ref(), a) {    if (a == that.alloc_ref()) {      std::swap(ctrl_, that.ctrl_);      std::swap(slots_, that.slots_);      std::swap(size_, that.size_);      std::swap(capacity_, that.capacity_);      std::swap(growth_left(), that.growth_left());      std::swap(infoz_, that.infoz_);    } else {      reserve(that.size());      // Note: this will copy elements of dense_set and unordered_set instead of      // moving them. This can be fixed if it ever becomes an issue.      for (auto& elem : that) insert(std::move(elem));    }  }  raw_hash_set& operator=(const raw_hash_set& that) {    raw_hash_set tmp(that,                     AllocTraits::propagate_on_container_copy_assignment::value                         ? that.alloc_ref()                         : alloc_ref());    swap(tmp);    return *this;  }  raw_hash_set& operator=(raw_hash_set&& that) noexcept(      absl::allocator_traits<allocator_type>::is_always_equal::value&&          std::is_nothrow_move_assignable<hasher>::value&&              std::is_nothrow_move_assignable<key_equal>::value) {    // TODO(sbenza): We should only use the operations from the noexcept clause    // to make sure we actually adhere to that contract.    return move_assign(        std::move(that),        typename AllocTraits::propagate_on_container_move_assignment());  }  ~raw_hash_set() { destroy_slots(); }  iterator begin() {    auto it = iterator_at(0);    it.skip_empty_or_deleted();    return it;  }  iterator end() { return {ctrl_ + capacity_}; }  const_iterator begin() const {    return const_cast<raw_hash_set*>(this)->begin();  }  const_iterator end() const { return const_cast<raw_hash_set*>(this)->end(); }  const_iterator cbegin() const { return begin(); }  const_iterator cend() const { return end(); }  bool empty() const { return !size(); }  size_t size() const { return size_; }  size_t capacity() const { return capacity_; }  size_t max_size() const { return (std::numeric_limits<size_t>::max)(); }  void clear() {    // Iterating over this container is O(bucket_count()). When bucket_count()    // is much greater than size(), iteration becomes prohibitively expensive.    // For clear() it is more important to reuse the allocated array when the    // container is small because allocation takes comparatively long time    // compared to destruction of the elements of the container. So we pick the    // largest bucket_count() threshold for which iteration is still fast and    // past that we simply deallocate the array.    if (capacity_ > 127) {      destroy_slots();    } else if (capacity_) {      for (size_t i = 0; i != capacity_; ++i) {        if (IsFull(ctrl_[i])) {          PolicyTraits::destroy(&alloc_ref(), slots_ + i);        }      }      size_ = 0;      reset_ctrl();      reset_growth_left();    }    assert(empty());    infoz_.RecordStorageChanged(size_, capacity_);  }  // This overload kicks in when the argument is an rvalue of insertable and  // decomposable type other than init_type.  //  //   flat_hash_map<std::string, int> m;  //   m.insert(std::make_pair("abc", 42));  template <class T, RequiresInsertable<T> = 0,            typename std::enable_if<IsDecomposable<T>::value, int>::type = 0,            T* = nullptr>  std::pair<iterator, bool> insert(T&& value) {    return emplace(std::forward<T>(value));  }  // This overload kicks in when the argument is a bitfield or an lvalue of  // insertable and decomposable type.  //  //   union { int n : 1; };  //   flat_hash_set<int> s;  //   s.insert(n);  //  //   flat_hash_set<std::string> s;  //   const char* p = "hello";  //   s.insert(p);  //  // TODO(romanp): Once we stop supporting gcc 5.1 and below, replace  // RequiresInsertable<T> with RequiresInsertable<const T&>.  // We are hitting this bug: https://godbolt.org/g/1Vht4f.  template <      class T, RequiresInsertable<T> = 0,      typename std::enable_if<IsDecomposable<const T&>::value, int>::type = 0>  std::pair<iterator, bool> insert(const T& value) {    return emplace(value);  }  // This overload kicks in when the argument is an rvalue of init_type. Its  // purpose is to handle brace-init-list arguments.  //  //   flat_hash_set<std::string, int> s;  //   s.insert({"abc", 42});  std::pair<iterator, bool> insert(init_type&& value) {    return emplace(std::move(value));  }  template <class T, RequiresInsertable<T> = 0,            typename std::enable_if<IsDecomposable<T>::value, int>::type = 0,            T* = nullptr>  iterator insert(const_iterator, T&& value) {    return insert(std::forward<T>(value)).first;  }  // TODO(romanp): Once we stop supporting gcc 5.1 and below, replace  // RequiresInsertable<T> with RequiresInsertable<const T&>.  // We are hitting this bug: https://godbolt.org/g/1Vht4f.  template <      class T, RequiresInsertable<T> = 0,      typename std::enable_if<IsDecomposable<const T&>::value, int>::type = 0>  iterator insert(const_iterator, const T& value) {    return insert(value).first;  }  iterator insert(const_iterator, init_type&& value) {    return insert(std::move(value)).first;  }  template <class InputIt>  void insert(InputIt first, InputIt last) {    for (; first != last; ++first) insert(*first);  }  template <class T, RequiresNotInit<T> = 0, RequiresInsertable<const T&> = 0>  void insert(std::initializer_list<T> ilist) {    insert(ilist.begin(), ilist.end());  }  void insert(std::initializer_list<init_type> ilist) {    insert(ilist.begin(), ilist.end());  }  insert_return_type<iterator, node_type> insert(node_type&& node) {    if (!node) return {end(), false, node_type()};    const auto& elem = PolicyTraits::element(node.slot());    auto res = PolicyTraits::apply(        InsertSlot<false>{*this, std::move(*node.slot())}, elem);    if (res.second) {      node.reset();      return {res.first, true, node_type()};    } else {      return {res.first, false, std::move(node)};    }  }  iterator insert(const_iterator, node_type&& node) {    return insert(std::move(node)).first;  }  // This overload kicks in if we can deduce the key from args. This enables us  // to avoid constructing value_type if an entry with the same key already  // exists.  //  // For example:  //  //   flat_hash_map<std::string, std::string> m = {{"abc", "def"}};  //   // Creates no std::string copies and makes no heap allocations.  //   m.emplace("abc", "xyz");  template <class... Args, typename std::enable_if<                               IsDecomposable<Args...>::value, int>::type = 0>  std::pair<iterator, bool> emplace(Args&&... args) {    return PolicyTraits::apply(EmplaceDecomposable{*this},                               std::forward<Args>(args)...);  }  // This overload kicks in if we cannot deduce the key from args. It constructs  // value_type unconditionally and then either moves it into the table or  // destroys.  template <class... Args, typename std::enable_if<                               !IsDecomposable<Args...>::value, int>::type = 0>  std::pair<iterator, bool> emplace(Args&&... args) {    typename std::aligned_storage<sizeof(slot_type), alignof(slot_type)>::type        raw;    slot_type* slot = reinterpret_cast<slot_type*>(&raw);    PolicyTraits::construct(&alloc_ref(), slot, std::forward<Args>(args)...);    const auto& elem = PolicyTraits::element(slot);    return PolicyTraits::apply(InsertSlot<true>{*this, std::move(*slot)}, elem);  }  template <class... Args>  iterator emplace_hint(const_iterator, Args&&... args) {    return emplace(std::forward<Args>(args)...).first;  }  // Extension API: support for lazy emplace.  //  // Looks up key in the table. If found, returns the iterator to the element.  // Otherwise calls f with one argument of type raw_hash_set::constructor. f  // MUST call raw_hash_set::constructor with arguments as if a  // raw_hash_set::value_type is constructed, otherwise the behavior is  // undefined.  //  // For example:  //  //   std::unordered_set<ArenaString> s;  //   // Makes ArenaStr even if "abc" is in the map.  //   s.insert(ArenaString(&arena, "abc"));  //  //   flat_hash_set<ArenaStr> s;  //   // Makes ArenaStr only if "abc" is not in the map.  //   s.lazy_emplace("abc", [&](const constructor& ctor) {  //     ctor(&arena, "abc");  //   });  //  // WARNING: This API is currently experimental. If there is a way to implement  // the same thing with the rest of the API, prefer that.  class constructor {    friend class raw_hash_set;   public:    template <class... Args>    void operator()(Args&&... args) const {      assert(*slot_);      PolicyTraits::construct(alloc_, *slot_, std::forward<Args>(args)...);      *slot_ = nullptr;    }   private:    constructor(allocator_type* a, slot_type** slot) : alloc_(a), slot_(slot) {}    allocator_type* alloc_;    slot_type** slot_;  };  template <class K = key_type, class F>  iterator lazy_emplace(const key_arg<K>& key, F&& f) {    auto res = find_or_prepare_insert(key);    if (res.second) {      slot_type* slot = slots_ + res.first;      std::forward<F>(f)(constructor(&alloc_ref(), &slot));      assert(!slot);    }    return iterator_at(res.first);  }  // Extension API: support for heterogeneous keys.  //  //   std::unordered_set<std::string> s;  //   // Turns "abc" into std::string.  //   s.erase("abc");  //  //   flat_hash_set<std::string> s;  //   // Uses "abc" directly without copying it into std::string.  //   s.erase("abc");  template <class K = key_type>  size_type erase(const key_arg<K>& key) {    auto it = find(key);    if (it == end()) return 0;    erase(it);    return 1;  }  // Erases the element pointed to by `it`.  Unlike `std::unordered_set::erase`,  // this method returns void to reduce algorithmic complexity to O(1).  In  // order to erase while iterating across a map, use the following idiom (which  // also works for standard containers):  //  // for (auto it = m.begin(), end = m.end(); it != end;) {  //   if (<pred>) {  //     m.erase(it++);  //   } else {  //     ++it;  //   }  // }  void erase(const_iterator cit) { erase(cit.inner_); }  // This overload is necessary because otherwise erase<K>(const K&) would be  // a better match if non-const iterator is passed as an argument.  void erase(iterator it) {    assert(it != end());    PolicyTraits::destroy(&alloc_ref(), it.slot_);    erase_meta_only(it);  }  iterator erase(const_iterator first, const_iterator last) {    while (first != last) {      erase(first++);    }    return last.inner_;  }  // Moves elements from `src` into `this`.  // If the element already exists in `this`, it is left unmodified in `src`.  template <typename H, typename E>  void merge(raw_hash_set<Policy, H, E, Alloc>& src) {  // NOLINT    assert(this != &src);    for (auto it = src.begin(), e = src.end(); it != e; ++it) {      if (PolicyTraits::apply(InsertSlot<false>{*this, std::move(*it.slot_)},                              PolicyTraits::element(it.slot_))              .second) {        src.erase_meta_only(it);      }    }  }  template <typename H, typename E>  void merge(raw_hash_set<Policy, H, E, Alloc>&& src) {    merge(src);  }  node_type extract(const_iterator position) {    node_type node(alloc_ref(), position.inner_.slot_);    erase_meta_only(position);    return node;  }  template <      class K = key_type,      typename std::enable_if<!std::is_same<K, iterator>::value, int>::type = 0>  node_type extract(const key_arg<K>& key) {    auto it = find(key);    return it == end() ? node_type() : extract(const_iterator{it});  }  void swap(raw_hash_set& that) noexcept(      IsNoThrowSwappable<hasher>() && IsNoThrowSwappable<key_equal>() &&      (!AllocTraits::propagate_on_container_swap::value ||       IsNoThrowSwappable<allocator_type>())) {    using std::swap;    swap(ctrl_, that.ctrl_);    swap(slots_, that.slots_);    swap(size_, that.size_);    swap(capacity_, that.capacity_);    swap(growth_left(), that.growth_left());    swap(hash_ref(), that.hash_ref());    swap(eq_ref(), that.eq_ref());    swap(infoz_, that.infoz_);    if (AllocTraits::propagate_on_container_swap::value) {      swap(alloc_ref(), that.alloc_ref());    } else {      // If the allocators do not compare equal it is officially undefined      // behavior. We choose to do nothing.    }  }  void rehash(size_t n) {    if (n == 0 && capacity_ == 0) return;    if (n == 0 && size_ == 0) {      destroy_slots();      infoz_.RecordStorageChanged(size_, capacity_);      return;    }    // bitor is a faster way of doing `max` here. We will round up to the next    // power-of-2-minus-1, so bitor is good enough.    auto m = NormalizeCapacity(n | GrowthToLowerboundCapacity(size()));    // n == 0 unconditionally rehashes as per the standard.    if (n == 0 || m > capacity_) {      resize(m);    }  }  void reserve(size_t n) { rehash(GrowthToLowerboundCapacity(n)); }  // Extension API: support for heterogeneous keys.  //  //   std::unordered_set<std::string> s;  //   // Turns "abc" into std::string.  //   s.count("abc");  //  //   ch_set<std::string> s;  //   // Uses "abc" directly without copying it into std::string.  //   s.count("abc");  template <class K = key_type>  size_t count(const key_arg<K>& key) const {    return find(key) == end() ? 0 : 1;  }  // Issues CPU prefetch instructions for the memory needed to find or insert  // a key.  Like all lookup functions, this support heterogeneous keys.  //  // NOTE: This is a very low level operation and should not be used without  // specific benchmarks indicating its importance.  template <class K = key_type>  void prefetch(const key_arg<K>& key) const {    (void)key;#if defined(__GNUC__)    auto seq = probe(hash_ref()(key));    __builtin_prefetch(static_cast<const void*>(ctrl_ + seq.offset()));    __builtin_prefetch(static_cast<const void*>(slots_ + seq.offset()));#endif  // __GNUC__  }  // The API of find() has two extensions.  //  // 1. The hash can be passed by the user. It must be equal to the hash of the  // key.  //  // 2. The type of the key argument doesn't have to be key_type. This is so  // called heterogeneous key support.  template <class K = key_type>  iterator find(const key_arg<K>& key, size_t hash) {    auto seq = probe(hash);    while (true) {      Group g{ctrl_ + seq.offset()};      for (int i : g.Match(H2(hash))) {        if (ABSL_PREDICT_TRUE(PolicyTraits::apply(                EqualElement<K>{key, eq_ref()},                PolicyTraits::element(slots_ + seq.offset(i)))))          return iterator_at(seq.offset(i));      }      if (ABSL_PREDICT_TRUE(g.MatchEmpty())) return end();      seq.next();    }  }  template <class K = key_type>  iterator find(const key_arg<K>& key) {    return find(key, hash_ref()(key));  }  template <class K = key_type>  const_iterator find(const key_arg<K>& key, size_t hash) const {    return const_cast<raw_hash_set*>(this)->find(key, hash);  }  template <class K = key_type>  const_iterator find(const key_arg<K>& key) const {    return find(key, hash_ref()(key));  }  template <class K = key_type>  bool contains(const key_arg<K>& key) const {    return find(key) != end();  }  template <class K = key_type>  std::pair<iterator, iterator> equal_range(const key_arg<K>& key) {    auto it = find(key);    if (it != end()) return {it, std::next(it)};    return {it, it};  }  template <class K = key_type>  std::pair<const_iterator, const_iterator> equal_range(      const key_arg<K>& key) const {    auto it = find(key);    if (it != end()) return {it, std::next(it)};    return {it, it};  }  size_t bucket_count() const { return capacity_; }  float load_factor() const {    return capacity_ ? static_cast<double>(size()) / capacity_ : 0.0;  }  float max_load_factor() const { return 1.0f; }  void max_load_factor(float) {    // Does nothing.  }  hasher hash_function() const { return hash_ref(); }  key_equal key_eq() const { return eq_ref(); }  allocator_type get_allocator() const { return alloc_ref(); }  friend bool operator==(const raw_hash_set& a, const raw_hash_set& b) {    if (a.size() != b.size()) return false;    const raw_hash_set* outer = &a;    const raw_hash_set* inner = &b;    if (outer->capacity() > inner->capacity()) std::swap(outer, inner);    for (const value_type& elem : *outer)      if (!inner->has_element(elem)) return false;    return true;  }  friend bool operator!=(const raw_hash_set& a, const raw_hash_set& b) {    return !(a == b);  }  friend void swap(raw_hash_set& a,                   raw_hash_set& b) noexcept(noexcept(a.swap(b))) {    a.swap(b);  } private:  template <class Container, typename Enabler>  friend struct absl::container_internal::hashtable_debug_internal::      HashtableDebugAccess;  struct FindElement {    template <class K, class... Args>    const_iterator operator()(const K& key, Args&&...) const {      return s.find(key);    }    const raw_hash_set& s;  };  struct HashElement {    template <class K, class... Args>    size_t operator()(const K& key, Args&&...) const {      return h(key);    }    const hasher& h;  };  template <class K1>  struct EqualElement {    template <class K2, class... Args>    bool operator()(const K2& lhs, Args&&...) const {      return eq(lhs, rhs);    }    const K1& rhs;    const key_equal& eq;  };  struct EmplaceDecomposable {    template <class K, class... Args>    std::pair<iterator, bool> operator()(const K& key, Args&&... args) const {      auto res = s.find_or_prepare_insert(key);      if (res.second) {        s.emplace_at(res.first, std::forward<Args>(args)...);      }      return {s.iterator_at(res.first), res.second};    }    raw_hash_set& s;  };  template <bool do_destroy>  struct InsertSlot {    template <class K, class... Args>    std::pair<iterator, bool> operator()(const K& key, Args&&...) && {      auto res = s.find_or_prepare_insert(key);      if (res.second) {        PolicyTraits::transfer(&s.alloc_ref(), s.slots_ + res.first, &slot);      } else if (do_destroy) {        PolicyTraits::destroy(&s.alloc_ref(), &slot);      }      return {s.iterator_at(res.first), res.second};    }    raw_hash_set& s;    // Constructed slot. Either moved into place or destroyed.    slot_type&& slot;  };  // "erases" the object from the container, except that it doesn't actually  // destroy the object. It only updates all the metadata of the class.  // This can be used in conjunction with Policy::transfer to move the object to  // another place.  void erase_meta_only(const_iterator it) {    assert(IsFull(*it.inner_.ctrl_) && "erasing a dangling iterator");    --size_;    const size_t index = it.inner_.ctrl_ - ctrl_;    const size_t index_before = (index - Group::kWidth) & capacity_;    const auto empty_after = Group(it.inner_.ctrl_).MatchEmpty();    const auto empty_before = Group(ctrl_ + index_before).MatchEmpty();    // We count how many consecutive non empties we have to the right and to the    // left of `it`. If the sum is >= kWidth then there is at least one probe    // window that might have seen a full group.    bool was_never_full =        empty_before && empty_after &&        static_cast<size_t>(empty_after.TrailingZeros() +                            empty_before.LeadingZeros()) < Group::kWidth;    set_ctrl(index, was_never_full ? kEmpty : kDeleted);    growth_left() += was_never_full;    infoz_.RecordErase();  }  void initialize_slots() {    assert(capacity_);    if (slots_ == nullptr) {      infoz_ = Sample();    }    auto layout = MakeLayout(capacity_);    char* mem = static_cast<char*>(        Allocate<Layout::Alignment()>(&alloc_ref(), layout.AllocSize()));    ctrl_ = reinterpret_cast<ctrl_t*>(layout.template Pointer<0>(mem));    slots_ = layout.template Pointer<1>(mem);    reset_ctrl();    reset_growth_left();    infoz_.RecordStorageChanged(size_, capacity_);  }  void destroy_slots() {    if (!capacity_) return;    for (size_t i = 0; i != capacity_; ++i) {      if (IsFull(ctrl_[i])) {        PolicyTraits::destroy(&alloc_ref(), slots_ + i);      }    }    auto layout = MakeLayout(capacity_);    // Unpoison before returning the memory to the allocator.    SanitizerUnpoisonMemoryRegion(slots_, sizeof(slot_type) * capacity_);    Deallocate<Layout::Alignment()>(&alloc_ref(), ctrl_, layout.AllocSize());    ctrl_ = EmptyGroup();    slots_ = nullptr;    size_ = 0;    capacity_ = 0;    growth_left() = 0;  }  void resize(size_t new_capacity) {    assert(IsValidCapacity(new_capacity));    auto* old_ctrl = ctrl_;    auto* old_slots = slots_;    const size_t old_capacity = capacity_;    capacity_ = new_capacity;    initialize_slots();    for (size_t i = 0; i != old_capacity; ++i) {      if (IsFull(old_ctrl[i])) {        size_t hash = PolicyTraits::apply(HashElement{hash_ref()},                                          PolicyTraits::element(old_slots + i));        size_t new_i = find_first_non_full(hash).offset;        set_ctrl(new_i, H2(hash));        PolicyTraits::transfer(&alloc_ref(), slots_ + new_i, old_slots + i);      }    }    if (old_capacity) {      SanitizerUnpoisonMemoryRegion(old_slots,                                    sizeof(slot_type) * old_capacity);      auto layout = MakeLayout(old_capacity);      Deallocate<Layout::Alignment()>(&alloc_ref(), old_ctrl,                                      layout.AllocSize());    }  }  void drop_deletes_without_resize() ABSL_ATTRIBUTE_NOINLINE {    assert(IsValidCapacity(capacity_));    // Algorithm:    // - mark all DELETED slots as EMPTY    // - mark all FULL slots as DELETED    // - for each slot marked as DELETED    //     hash = Hash(element)    //     target = find_first_non_full(hash)    //     if target is in the same group    //       mark slot as FULL    //     else if target is EMPTY    //       transfer element to target    //       mark slot as EMPTY    //       mark target as FULL    //     else if target is DELETED    //       swap current element with target element    //       mark target as FULL    //       repeat procedure for current slot with moved from element (target)    ConvertDeletedToEmptyAndFullToDeleted(ctrl_, capacity_);    typename std::aligned_storage<sizeof(slot_type), alignof(slot_type)>::type        raw;    slot_type* slot = reinterpret_cast<slot_type*>(&raw);    for (size_t i = 0; i != capacity_; ++i) {      if (!IsDeleted(ctrl_[i])) continue;      size_t hash = PolicyTraits::apply(HashElement{hash_ref()},                                        PolicyTraits::element(slots_ + i));      size_t new_i = find_first_non_full(hash).offset;      // Verify if the old and new i fall within the same group wrt the hash.      // If they do, we don't need to move the object as it falls already in the      // best probe we can.      const auto probe_index = [&](size_t pos) {        return ((pos - probe(hash).offset()) & capacity_) / Group::kWidth;      };      // Element doesn't move.      if (ABSL_PREDICT_TRUE(probe_index(new_i) == probe_index(i))) {        set_ctrl(i, H2(hash));        continue;      }      if (IsEmpty(ctrl_[new_i])) {        // Transfer element to the empty spot.        // set_ctrl poisons/unpoisons the slots so we have to call it at the        // right time.        set_ctrl(new_i, H2(hash));        PolicyTraits::transfer(&alloc_ref(), slots_ + new_i, slots_ + i);        set_ctrl(i, kEmpty);      } else {        assert(IsDeleted(ctrl_[new_i]));        set_ctrl(new_i, H2(hash));        // Until we are done rehashing, DELETED marks previously FULL slots.        // Swap i and new_i elements.        PolicyTraits::transfer(&alloc_ref(), slot, slots_ + i);        PolicyTraits::transfer(&alloc_ref(), slots_ + i, slots_ + new_i);        PolicyTraits::transfer(&alloc_ref(), slots_ + new_i, slot);        --i;  // repeat      }    }    reset_growth_left();  }  void rehash_and_grow_if_necessary() {    if (capacity_ == 0) {      resize(Group::kWidth - 1);    } else if (size() <= CapacityToGrowth(capacity()) / 2) {      // Squash DELETED without growing if there is enough capacity.      drop_deletes_without_resize();    } else {      // Otherwise grow the container.      resize(capacity_ * 2 + 1);    }  }  bool has_element(const value_type& elem) const {    size_t hash = PolicyTraits::apply(HashElement{hash_ref()}, elem);    auto seq = probe(hash);    while (true) {      Group g{ctrl_ + seq.offset()};      for (int i : g.Match(H2(hash))) {        if (ABSL_PREDICT_TRUE(PolicyTraits::element(slots_ + seq.offset(i)) ==                              elem))          return true;      }      if (ABSL_PREDICT_TRUE(g.MatchEmpty())) return false;      seq.next();      assert(seq.index() < capacity_ && "full table!");    }    return false;  }  // Probes the raw_hash_set with the probe sequence for hash and returns the  // pointer to the first empty or deleted slot.  // NOTE: this function must work with tables having both kEmpty and kDelete  // in one group. Such tables appears during drop_deletes_without_resize.  //  // This function is very useful when insertions happen and:  // - the input is already a set  // - there are enough slots  // - the element with the hash is not in the table  struct FindInfo {    size_t offset;    size_t probe_length;  };  FindInfo find_first_non_full(size_t hash) {    auto seq = probe(hash);    while (true) {      Group g{ctrl_ + seq.offset()};      auto mask = g.MatchEmptyOrDeleted();      if (mask) {#if !defined(NDEBUG)        // We want to force small tables to have random entries too, so        // in debug build we will randomly insert in either the front or back of        // the group.        // TODO(kfm,sbenza): revisit after we do unconditional mixing        if (ShouldInsertBackwards(hash, ctrl_))          return {seq.offset(mask.HighestBitSet()), seq.index()};        else          return {seq.offset(mask.LowestBitSet()), seq.index()};#else        return {seq.offset(mask.LowestBitSet()), seq.index()};#endif      }      assert(seq.index() < capacity_ && "full table!");      seq.next();    }  }  // TODO(alkis): Optimize this assuming *this and that don't overlap.  raw_hash_set& move_assign(raw_hash_set&& that, std::true_type) {    raw_hash_set tmp(std::move(that));    swap(tmp);    return *this;  }  raw_hash_set& move_assign(raw_hash_set&& that, std::false_type) {    raw_hash_set tmp(std::move(that), alloc_ref());    swap(tmp);    return *this;  } protected:  template <class K>  std::pair<size_t, bool> find_or_prepare_insert(const K& key) {    auto hash = hash_ref()(key);    auto seq = probe(hash);    while (true) {      Group g{ctrl_ + seq.offset()};      for (int i : g.Match(H2(hash))) {        if (ABSL_PREDICT_TRUE(PolicyTraits::apply(                EqualElement<K>{key, eq_ref()},                PolicyTraits::element(slots_ + seq.offset(i)))))          return {seq.offset(i), false};      }      if (ABSL_PREDICT_TRUE(g.MatchEmpty())) break;      seq.next();    }    return {prepare_insert(hash), true};  }  size_t prepare_insert(size_t hash) ABSL_ATTRIBUTE_NOINLINE {    auto target = find_first_non_full(hash);    if (ABSL_PREDICT_FALSE(growth_left() == 0 &&                           !IsDeleted(ctrl_[target.offset]))) {      rehash_and_grow_if_necessary();      target = find_first_non_full(hash);    }    ++size_;    growth_left() -= IsEmpty(ctrl_[target.offset]);    set_ctrl(target.offset, H2(hash));    infoz_.RecordInsert(hash, target.probe_length);    return target.offset;  }  // Constructs the value in the space pointed by the iterator. This only works  // after an unsuccessful find_or_prepare_insert() and before any other  // modifications happen in the raw_hash_set.  //  // PRECONDITION: i is an index returned from find_or_prepare_insert(k), where  // k is the key decomposed from `forward<Args>(args)...`, and the bool  // returned by find_or_prepare_insert(k) was true.  // POSTCONDITION: *m.iterator_at(i) == value_type(forward<Args>(args)...).  template <class... Args>  void emplace_at(size_t i, Args&&... args) {    PolicyTraits::construct(&alloc_ref(), slots_ + i,                            std::forward<Args>(args)...);    assert(PolicyTraits::apply(FindElement{*this}, *iterator_at(i)) ==               iterator_at(i) &&           "constructed value does not match the lookup key");  }  iterator iterator_at(size_t i) { return {ctrl_ + i, slots_ + i}; }  const_iterator iterator_at(size_t i) const { return {ctrl_ + i, slots_ + i}; } private:  friend struct RawHashSetTestOnlyAccess;  probe_seq<Group::kWidth> probe(size_t hash) const {    return probe_seq<Group::kWidth>(H1(hash, ctrl_), capacity_);  }  // Reset all ctrl bytes back to kEmpty, except the sentinel.  void reset_ctrl() {    std::memset(ctrl_, kEmpty, capacity_ + Group::kWidth);    ctrl_[capacity_] = kSentinel;    SanitizerPoisonMemoryRegion(slots_, sizeof(slot_type) * capacity_);  }  void reset_growth_left() {    growth_left() = CapacityToGrowth(capacity()) - size_;  }  // Sets the control byte, and if `i < Group::kWidth`, set the cloned byte at  // the end too.  void set_ctrl(size_t i, ctrl_t h) {    assert(i < capacity_);    if (IsFull(h)) {      SanitizerUnpoisonObject(slots_ + i);    } else {      SanitizerPoisonObject(slots_ + i);    }    ctrl_[i] = h;    ctrl_[((i - Group::kWidth) & capacity_) + Group::kWidth] = h;  }  size_t& growth_left() { return settings_.template get<0>(); }  hasher& hash_ref() { return settings_.template get<1>(); }  const hasher& hash_ref() const { return settings_.template get<1>(); }  key_equal& eq_ref() { return settings_.template get<2>(); }  const key_equal& eq_ref() const { return settings_.template get<2>(); }  allocator_type& alloc_ref() { return settings_.template get<3>(); }  const allocator_type& alloc_ref() const {    return settings_.template get<3>();  }  // TODO(alkis): Investigate removing some of these fields:  // - ctrl/slots can be derived from each other  // - size can be moved into the slot array  ctrl_t* ctrl_ = EmptyGroup();    // [(capacity + 1) * ctrl_t]  slot_type* slots_ = nullptr;     // [capacity * slot_type]  size_t size_ = 0;                // number of full slots  size_t capacity_ = 0;            // total number of slots  HashtablezInfoHandle infoz_;  absl::container_internal::CompressedTuple<size_t /* growth_left */, hasher,                                            key_equal, allocator_type>      settings_{0, hasher{}, key_equal{}, allocator_type{}};};namespace hashtable_debug_internal {template <typename Set>struct HashtableDebugAccess<Set, absl::void_t<typename Set::raw_hash_set>> {  using Traits = typename Set::PolicyTraits;  using Slot = typename Traits::slot_type;  static size_t GetNumProbes(const Set& set,                             const typename Set::key_type& key) {    size_t num_probes = 0;    size_t hash = set.hash_ref()(key);    auto seq = set.probe(hash);    while (true) {      container_internal::Group g{set.ctrl_ + seq.offset()};      for (int i : g.Match(container_internal::H2(hash))) {        if (Traits::apply(                typename Set::template EqualElement<typename Set::key_type>{                    key, set.eq_ref()},                Traits::element(set.slots_ + seq.offset(i))))          return num_probes;        ++num_probes;      }      if (g.MatchEmpty()) return num_probes;      seq.next();      ++num_probes;    }  }  static size_t AllocatedByteSize(const Set& c) {    size_t capacity = c.capacity_;    if (capacity == 0) return 0;    auto layout = Set::MakeLayout(capacity);    size_t m = layout.AllocSize();    size_t per_slot = Traits::space_used(static_cast<const Slot*>(nullptr));    if (per_slot != ~size_t{}) {      m += per_slot * c.size();    } else {      for (size_t i = 0; i != capacity; ++i) {        if (container_internal::IsFull(c.ctrl_[i])) {          m += Traits::space_used(c.slots_ + i);        }      }    }    return m;  }  static size_t LowerBoundAllocatedByteSize(size_t size) {    size_t capacity = GrowthToLowerboundCapacity(size);    if (capacity == 0) return 0;    auto layout = Set::MakeLayout(NormalizeCapacity(capacity));    size_t m = layout.AllocSize();    size_t per_slot = Traits::space_used(static_cast<const Slot*>(nullptr));    if (per_slot != ~size_t{}) {      m += per_slot * size;    }    return m;  }};}  // namespace hashtable_debug_internal}  // namespace container_internal}  // namespace absl#endif  // ABSL_CONTAINER_INTERNAL_RAW_HASH_SET_H_
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