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abseil-cpp/absl/container/internal/raw_hash_set.h

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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/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, 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);
}
// 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);
}
// 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 = node_handle<Policy, hash_policy_traits<Policy>, Alloc>;
using insert_return_type = InsertReturnType<iterator, node_type>;
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)(); }
ABSL_ATTRIBUTE_REINITIALIZES 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(0, 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 insert(node_type&& node) {
if (!node) return {end(), false, node_type()};
const auto& elem = PolicyTraits::element(CommonAccess::GetSlot(node));
auto res = PolicyTraits::apply(
InsertSlot<false>{*this, std::move(*CommonAccess::GetSlot(node))},
elem);
if (res.second) {
CommonAccess::Reset(&node);
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) {
auto node =
CommonAccess::Make<node_type>(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(0, 0);
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();
size_t total_probe_length = 0;
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));
auto target = find_first_non_full(hash);
size_t new_i = target.offset;
total_probe_length += target.probe_length;
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());
}
infoz_.RecordRehash(total_probe_length);
}
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;
size_t total_probe_length = 0;
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));
auto target = find_first_non_full(hash);
size_t new_i = target.offset;
total_probe_length += target.probe_length;
// 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();
infoz_.RecordRehash(total_probe_length);
}
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_