diff options
Diffstat (limited to 'absl/container/internal/raw_hash_set.h')
| -rw-r--r-- | absl/container/internal/raw_hash_set.h | 1950 |
1 files changed, 1950 insertions, 0 deletions
diff --git a/absl/container/internal/raw_hash_set.h b/absl/container/internal/raw_hash_set.h new file mode 100644 index 00000000..0c42e4ae --- /dev/null +++ b/absl/container/internal/raw_hash_set.h @@ -0,0 +1,1950 @@ +// 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_ + +#ifndef SWISSTABLE_HAVE_SSE2 +#if defined(__SSE2__) || \ + (defined(_MSC_VER) && \ + (defined(_M_X64) || (defined(_M_IX86) && _M_IX86_FP >= 2))) +#define SWISSTABLE_HAVE_SSE2 1 +#else +#define SWISSTABLE_HAVE_SSE2 0 +#endif +#endif + +#ifndef SWISSTABLE_HAVE_SSSE3 +#ifdef __SSSE3__ +#define SWISSTABLE_HAVE_SSSE3 1 +#else +#define SWISSTABLE_HAVE_SSSE3 0 +#endif +#endif + +#if SWISSTABLE_HAVE_SSSE3 && !SWISSTABLE_HAVE_SSE2 +#error "Bad configuration!" +#endif + +#if SWISSTABLE_HAVE_SSE2 +#include <emmintrin.h> +#endif + +#if SWISSTABLE_HAVE_SSSE3 +#include <tmmintrin.h> +#endif + +#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/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/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 { +inline namespace lts_2018_12_18 { +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 {}; + +template <class, class = void> +struct IsTransparent : std::false_type {}; +template <class T> +struct IsTransparent<T, absl::void_t<typename T::is_transparent>> + : 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, 3 +template <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_SSE2 + +struct 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_SSE2 +using Group = GroupSse2Impl; +#else +using Group = GroupPortableImpl; +#endif + +template <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 -> DELETED +inline 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); +} + +// 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; +}; + +// Helper trait to allow or disallow arbitrary keys when the hash and +// eq functions are transparent. +// It is very important that the inner template is an alias and that the type it +// produces is not a dependent type. Otherwise, type deduction would fail. +template <bool is_transparent> +struct KeyArg { + // Transparent. Forward `K`. + template <typename K, typename key_type> + using type = K; +}; + +template <> +struct KeyArg<false> { + // Not transparent. Always use `key_type`. + template <typename K, typename key_type> + using type = key_type; +}; + +// 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 = container_internal::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; + 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); + growth_left() = static_cast<size_t>(capacity_ * kMaxLoadFactor); + 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); + const size_t i = find_first_non_full(hash); + set_ctrl(i, H2(hash)); + emplace_at(i, v); + } + 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)), + // 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()); + } 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(); + growth_left() = static_cast<size_t>(capacity_ * kMaxLoadFactor); + } + assert(empty()); + } + + // 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()); + 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) return destroy_slots(); + auto m = NormalizeCapacity(std::max(n, NumSlotsFast(size()))); + // n == 0 unconditionally rehashes as per the standard. + if (n == 0 || m > capacity_) { + resize(m); + } + } + + void reserve(size_t n) { + rehash(NumSlotsFast(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; + }; + + // Computes std::ceil(n / kMaxLoadFactor). Faster than calling std::ceil. + static inline size_t NumSlotsFast(size_t n) { + return static_cast<size_t>( + (n * kMaxLoadFactorDenominator + (kMaxLoadFactorNumerator - 1)) / + kMaxLoadFactorNumerator); + } + + // "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; + } + + void initialize_slots() { + assert(capacity_); + 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(); + growth_left() = static_cast<size_t>(capacity_ * kMaxLoadFactor) - size_; + } + + 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); + 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); + + // 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 + } + } + growth_left() = static_cast<size_t>(capacity_ * kMaxLoadFactor) - size_; + } + + void rehash_and_grow_if_necessary() { + if (capacity_ == 0) { + resize(Group::kWidth - 1); + } else if (size() <= kMaxLoadFactor / 2 * capacity_) { + // 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 + size_t 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()); + else + return seq.offset(mask.LowestBitSet()); +#else + return seq.offset(mask.LowestBitSet()); +#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 { + size_t target = find_first_non_full(hash); + if (ABSL_PREDICT_FALSE(growth_left() == 0 && !IsDeleted(ctrl_[target]))) { + rehash_and_grow_if_necessary(); + target = find_first_non_full(hash); + } + ++size_; + growth_left() -= IsEmpty(ctrl_[target]); + set_ctrl(target, H2(hash)); + return target; + } + + // 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_); + } + + // 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>(); + } + + // On average each group has 2 empty slot (for the vectorized case). + static constexpr int64_t kMaxLoadFactorNumerator = 14; + static constexpr int64_t kMaxLoadFactorDenominator = 16; + static constexpr float kMaxLoadFactor = + 1.0 * kMaxLoadFactorNumerator / kMaxLoadFactorDenominator; + + // 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 + 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 = container_internal::NormalizeCapacity( + std::ceil(size / Set::kMaxLoadFactor)); + 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 * size; + } + return m; + } +}; + +} // namespace hashtable_debug_internal +} // namespace container_internal +} // inline namespace lts_2018_12_18 +} // namespace absl + +#endif // ABSL_CONTAINER_INTERNAL_RAW_HASH_SET_H_ |