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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
//
// https://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
//
// 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
//
// # Table Layout
//
// A raw_hash_set's backing array consists of control bytes followed by slots
// that may or may not contain objects.
//
// The layout of the backing array, for `capacity` slots, is thus, as a
// pseudo-struct:
//
// struct BackingArray {
// // Control bytes for the "real" slots.
// ctrl_t ctrl[capacity];
// // Always `ctrl_t::kSentinel`. This is used by iterators to find when to
// // stop and serves no other purpose.
// ctrl_t sentinel;
// // A copy of the first `kWidth - 1` elements of `ctrl`. This is used so
// // that if a probe sequence picks a value near the end of `ctrl`,
// // `Group` will have valid control bytes to look at.
// ctrl_t clones[kWidth - 1];
// // The actual slot data.
// slot_type slots[capacity];
// };
//
// The length of this array is computed by `AllocSize()` below.
//
// Control bytes (`ctrl_t`) are bytes (collected into groups of a
// platform-specific size) that define the state of the corresponding slot in
// the slot array. Group manipulation is tightly optimized to be as efficient
// as possible: SSE and friends on x86, clever bit operations on other arches.
//
// Group 1 Group 2 Group 3
// +---------------+---------------+---------------+
// | | | | | | | | | | | | | | | | | | | | | | | | |
// +---------------+---------------+---------------+
//
// Each control byte is either a special value for empty slots, deleted slots
// (sometimes called *tombstones*), and a special end-of-table marker used by
// iterators, or, if occupied, seven bits (H2) from the hash of the value in the
// corresponding slot.
//
// Storing control bytes in a separate array also has beneficial cache effects,
// since more logical slots will fit into a cache line.
//
// # Hashing
//
// We compute two separate hashes, `H1` and `H2`, from the hash of an object.
// `H1(hash(x))` is an index into `slots`, and essentially the starting point
// for the probe sequence. `H2(hash(x))` is a 7-bit value used to filter out
// objects that cannot possibly be the one we are looking for.
//
// # Table operations.
//
// The key operations are `insert`, `find`, and `erase`.
//
// Since `insert` and `erase` are implemented in terms of `find`, we describe
// `find` first. To `find` a value `x`, we compute `hash(x)`. From
// `H1(hash(x))` and the capacity, we construct a `probe_seq` that visits every
// group of slots in some interesting order.
//
// We now walk through these indices. At each index, we select the entire group
// starting with that index and extract potential candidates: occupied slots
// with a control byte equal to `H2(hash(x))`. If we find an empty slot in the
// group, we stop and return an error. Each candidate slot `y` is compared with
// `x`; if `x == y`, we are done and return `&y`; otherwise we contine to the
// next probe index. Tombstones effectively behave like full slots that never
// match the value we're looking for.
//
// The `H2` bits ensure when we compare a slot to an object with `==`, we are
// likely to have actually found the object. That is, the chance is low that
// `==` is called and returns `false`. Thus, when we search for an object, we
// are unlikely to call `==` many times. This likelyhood can be analyzed as
// follows (assuming that H2 is a random enough hash function).
//
// Let's assume that there are `k` "wrong" objects that must be examined in a
// probe sequence. For example, when doing a `find` on an object that is in the
// table, `k` is the number of objects between the start of the probe sequence
// and the final found object (not including the final found object). The
// expected number of objects with an H2 match is then `k/128`. Measurements
// and analysis indicate that even at high load factors, `k` is less than 32,
// meaning that the number of "false positive" comparisons we must perform is
// less than 1/8 per `find`.
// `insert` is implemented in terms of `unchecked_insert`, which inserts a
// value presumed to not be in the table (violating this requirement will cause
// the table to behave erratically). Given `x` and its hash `hash(x)`, to insert
// it, we construct a `probe_seq` once again, and use it to find the first
// group with an unoccupied (empty *or* deleted) slot. We place `x` into the
// first such slot in the group and mark it as full with `x`'s H2.
//
// To `insert`, we compose `unchecked_insert` with `find`. We compute `h(x)` and
// perform a `find` to see if it's already present; if it is, we're done. If
// it's not, we may decide the table is getting overcrowded (i.e. the load
// factor is greater than 7/8 for big tables; `is_small()` tables use a max load
// factor of 1); in this case, we allocate a bigger array, `unchecked_insert`
// each element of the table into the new array (we know that no insertion here
// will insert an already-present value), and discard the old backing array. At
// this point, we may `unchecked_insert` the value `x`.
//
// Below, `unchecked_insert` is partly implemented by `prepare_insert`, which
// presents a viable, initialized slot pointee to the caller.
//
// `erase` is implemented in terms of `erase_at`, which takes an index to a
// slot. Given an offset, we simply create a tombstone and destroy its contents.
// If we can prove that the slot would not appear in a probe sequence, we can
// make the slot as empty, instead. We can prove this by observing that if a
// group has any empty slots, it has never been full (assuming we never create
// an empty slot in a group with no empties, which this heuristic guarantees we
// never do) and find would stop at this group anyways (since it does not probe
// beyond groups with empties).
//
// `erase` is `erase_at` composed with `find`: if we
// have a value `x`, we can perform a `find`, and then `erase_at` the resulting
// slot.
//
// To iterate, we simply traverse the array, skipping empty and deleted slots
// and stopping when we hit a `kSentinel`.
#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/config.h"
#include "absl/base/internal/endian.h"
#include "absl/base/internal/prefetch.h"
#include "absl/base/optimization.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/memory/memory.h"
#include "absl/meta/type_traits.h"
#include "absl/numeric/bits.h"
#include "absl/utility/utility.h"
#ifdef ABSL_INTERNAL_HAVE_SSE2
#include <emmintrin.h>
#endif
#ifdef ABSL_INTERNAL_HAVE_SSSE3
#include <tmmintrin.h>
#endif
#ifdef _MSC_VER
#include <intrin.h>
#endif
#ifdef ABSL_INTERNAL_HAVE_ARM_NEON
#include <arm_neon.h>
#endif
namespace absl {
ABSL_NAMESPACE_BEGIN
namespace container_internal {
template <typename AllocType>
void SwapAlloc(AllocType& lhs, AllocType& rhs,
std::true_type /* propagate_on_container_swap */) {
using std::swap;
swap(lhs, rhs);
}
template <typename AllocType>
void SwapAlloc(AllocType& /*lhs*/, AllocType& /*rhs*/,
std::false_type /* propagate_on_container_swap */) {}
// The state for a probe sequence.
//
// Currently, the sequence is a triangular progression of the form
//
// p(i) := Width * (i^2 + i)/2 + hash (mod mask + 1)
//
// The use of `Width` ensures that each probe step does not overlap groups;
// the sequence effectively outputs the addresses of *groups* (although not
// necessarily aligned to any boundary). The `Group` machinery allows us
// to check an entire group with minimal branching.
//
// Wrapping around at `mask + 1` is important, but not for the obvious reason.
// As described above, the first few entries of the control byte array
// are mirrored at the end of the array, which `Group` will find and use
// for selecting candidates. However, when those candidates' slots are
// actually inspected, there are no corresponding slots for the cloned bytes,
// so we need to make sure we've treated those offsets as "wrapping around".
//
// It turns out that this probe sequence visits every group exactly once if the
// number of groups is a power of two, since (i^2+i)/2 is a bijection in
// Z/(2^m). See https://en.wikipedia.org/wiki/Quadratic_probing
template <size_t Width>
class probe_seq {
public:
// Creates a new probe sequence using `hash` as the initial value of the
// sequence and `mask` (usually the capacity of the table) as the mask to
// apply to each value in the progression.
probe_seq(size_t hash, size_t mask) {
assert(((mask + 1) & mask) == 0 && "not a mask");
mask_ = mask;
offset_ = hash & mask_;
}
// The offset within the table, i.e., the value `p(i)` above.
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, a multiple of `Width`.
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(std::true_type = {} /* is_swappable */) {
using std::swap;
return noexcept(swap(std::declval<T&>(), std::declval<T&>()));
}
template <class T>
constexpr bool IsNoThrowSwappable(std::false_type /* is_swappable */) {
return false;
}
template <typename T>
uint32_t TrailingZeros(T x) {
ABSL_ASSUME(x != 0);
return static_cast<uint32_t>(countr_zero(x));
}
// An abstract bitmask, such as that emitted by a SIMD instruction.
//
// Specifically, this type implements a simple bitset whose representation is
// controlled by `SignificantBits` and `Shift`. `SignificantBits` is the number
// of abstract bits in the bitset, while `Shift` is the log-base-two of the
// width of an abstract bit in the representation.
// This mask provides operations for any number of real bits set in an abstract
// bit. To add iteration on top of that, implementation must guarantee no more
// than one real bit is set in an abstract bit.
template <class T, int SignificantBits, int Shift = 0>
class NonIterableBitMask {
public:
explicit NonIterableBitMask(T mask) : mask_(mask) {}
explicit operator bool() const { return this->mask_ != 0; }
// Returns the index of the lowest *abstract* bit set in `self`.
uint32_t LowestBitSet() const {
return container_internal::TrailingZeros(mask_) >> Shift;
}
// Returns the index of the highest *abstract* bit set in `self`.
uint32_t HighestBitSet() const {
return static_cast<uint32_t>((bit_width(mask_) - 1) >> Shift);
}
// Return the number of trailing zero *abstract* bits.
uint32_t TrailingZeros() const {
return container_internal::TrailingZeros(mask_) >> Shift;
}
// Return the number of leading zero *abstract* bits.
uint32_t LeadingZeros() const {
constexpr int total_significant_bits = SignificantBits << Shift;
constexpr int extra_bits = sizeof(T) * 8 - total_significant_bits;
return static_cast<uint32_t>(countl_zero(mask_ << extra_bits)) >> Shift;
}
T mask_;
};
// Mask that can be iterable
//
// For example, when `SignificantBits` is 16 and `Shift` is zero, this is just
// an ordinary 16-bit bitset occupying the low 16 bits of `mask`. When
// `SignificantBits` is 8 and `Shift` is 3, abstract bits are represented as
// the bytes `0x00` and `0x80`, and it occupies all 64 bits of the bitmask.
//
// For example:
// for (int i : BitMask<uint32_t, 16>(0b101)) -> 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 : public NonIterableBitMask<T, SignificantBits, Shift> {
using Base = NonIterableBitMask<T, SignificantBits, Shift>;
static_assert(std::is_unsigned<T>::value, "");
static_assert(Shift == 0 || Shift == 3, "");
public:
explicit BitMask(T mask) : Base(mask) {}
// BitMask is an iterator over the indices of its abstract bits.
using value_type = int;
using iterator = BitMask;
using const_iterator = BitMask;
BitMask& operator++() {
this->mask_ &= (this->mask_ - 1);
return *this;
}
uint32_t operator*() const { return Base::LowestBitSet(); }
BitMask begin() const { return *this; }
BitMask end() const { return BitMask(0); }
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_;
}
};
using h2_t = uint8_t;
// The values here are selected for maximum performance. See the static asserts
// below for details.
// A `ctrl_t` is a single control byte, which can have one of four
// states: empty, deleted, full (which has an associated seven-bit h2_t value)
// and the sentinel. They have the following bit patterns:
//
// empty: 1 0 0 0 0 0 0 0
// deleted: 1 1 1 1 1 1 1 0
// full: 0 h h h h h h h // h represents the hash bits.
// sentinel: 1 1 1 1 1 1 1 1
//
// These values are specifically tuned for SSE-flavored SIMD.
// The static_asserts below detail the source of these choices.
//
// We use an enum class so that when strict aliasing is enabled, the compiler
// knows ctrl_t doesn't alias other types.
enum class ctrl_t : int8_t {
kEmpty = -128, // 0b10000000
kDeleted = -2, // 0b11111110
kSentinel = -1, // 0b11111111
};
static_assert(
(static_cast<int8_t>(ctrl_t::kEmpty) &
static_cast<int8_t>(ctrl_t::kDeleted) &
static_cast<int8_t>(ctrl_t::kSentinel) & 0x80) != 0,
"Special markers need to have the MSB to make checking for them efficient");
static_assert(
ctrl_t::kEmpty < ctrl_t::kSentinel && ctrl_t::kDeleted < ctrl_t::kSentinel,
"ctrl_t::kEmpty and ctrl_t::kDeleted must be smaller than "
"ctrl_t::kSentinel to make the SIMD test of IsEmptyOrDeleted() efficient");
static_assert(
ctrl_t::kSentinel == static_cast<ctrl_t>(-1),
"ctrl_t::kSentinel must be -1 to elide loading it from memory into SIMD "
"registers (pcmpeqd xmm, xmm)");
static_assert(ctrl_t::kEmpty == static_cast<ctrl_t>(-128),
"ctrl_t::kEmpty must be -128 to make the SIMD check for its "
"existence efficient (psignb xmm, xmm)");
static_assert(
(~static_cast<int8_t>(ctrl_t::kEmpty) &
~static_cast<int8_t>(ctrl_t::kDeleted) &
static_cast<int8_t>(ctrl_t::kSentinel) & 0x7F) != 0,
"ctrl_t::kEmpty and ctrl_t::kDeleted must share an unset bit that is not "
"shared by ctrl_t::kSentinel to make the scalar test for "
"MaskEmptyOrDeleted() efficient");
static_assert(ctrl_t::kDeleted == static_cast<ctrl_t>(-2),
"ctrl_t::kDeleted must be -2 to make the implementation of "
"ConvertSpecialToEmptyAndFullToDeleted efficient");
ABSL_DLL extern const ctrl_t kEmptyGroup[16];
// Returns a pointer to a control byte group that can be used by empty tables.
inline ctrl_t* EmptyGroup() {
// Const must be cast away here; no uses of this function will actually write
// to it, because it is only used for empty tables.
return const_cast<ctrl_t*>(kEmptyGroup);
}
// Mixes a randomly generated per-process seed with `hash` and `ctrl` to
// randomize insertion order within groups.
bool ShouldInsertBackwards(size_t hash, const ctrl_t* ctrl);
// Returns a per-table, hash salt, which changes on resize. This gets mixed into
// H1 to randomize iteration order per-table.
//
// The seed consists of the ctrl_ pointer, which adds enough entropy to ensure
// non-determinism of iteration order in most cases.
inline size_t PerTableSalt(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;
}
// Extracts the H1 portion of a hash: 57 bits mixed with a per-table salt.
inline size_t H1(size_t hash, const ctrl_t* ctrl) {
return (hash >> 7) ^ PerTableSalt(ctrl);
}
// Extracts the H2 portion of a hash: the 7 bits not used for H1.
//
// These are used as an occupied control byte.
inline h2_t H2(size_t hash) { return hash & 0x7F; }
// Helpers for checking the state of a control byte.
inline bool IsEmpty(ctrl_t c) { return c == ctrl_t::kEmpty; }
inline bool IsFull(ctrl_t c) { return c >= static_cast<ctrl_t>(0); }
inline bool IsDeleted(ctrl_t c) { return c == ctrl_t::kDeleted; }
inline bool IsEmptyOrDeleted(ctrl_t c) { return c < ctrl_t::kSentinel; }
#ifdef ABSL_INTERNAL_HAVE_SSE2
// Quick reference guide for intrinsics used below:
//
// * __m128i: An XMM (128-bit) word.
//
// * _mm_setzero_si128: Returns a zero vector.
// * _mm_set1_epi8: Returns a vector with the same i8 in each lane.
//
// * _mm_subs_epi8: Saturating-subtracts two i8 vectors.
// * _mm_and_si128: Ands two i128s together.
// * _mm_or_si128: Ors two i128s together.
// * _mm_andnot_si128: And-nots two i128s together.
//
// * _mm_cmpeq_epi8: Component-wise compares two i8 vectors for equality,
// filling each lane with 0x00 or 0xff.
// * _mm_cmpgt_epi8: Same as above, but using > rather than ==.
//
// * _mm_loadu_si128: Performs an unaligned load of an i128.
// * _mm_storeu_si128: Performs an unaligned store of an i128.
//
// * _mm_sign_epi8: Retains, negates, or zeroes each i8 lane of the first
// argument if the corresponding lane of the second
// argument is positive, negative, or zero, respectively.
// * _mm_movemask_epi8: Selects the sign bit out of each i8 lane and produces a
// bitmask consisting of those bits.
// * _mm_shuffle_epi8: Selects i8s from the first argument, using the low
// four bits of each i8 lane in the second argument as
// indices.
// 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(static_cast<char>(hash));
return BitMask<uint32_t, kWidth>(
static_cast<uint32_t>(_mm_movemask_epi8(_mm_cmpeq_epi8(match, ctrl))));
}
// Returns a bitmask representing the positions of empty slots.
NonIterableBitMask<uint32_t, kWidth> MaskEmpty() const {
#ifdef ABSL_INTERNAL_HAVE_SSSE3
// This only works because ctrl_t::kEmpty is -128.
return NonIterableBitMask<uint32_t, kWidth>(
static_cast<uint32_t>(_mm_movemask_epi8(_mm_sign_epi8(ctrl, ctrl))));
#else
auto match = _mm_set1_epi8(static_cast<char>(ctrl_t::kEmpty));
return NonIterableBitMask<uint32_t, kWidth>(
static_cast<uint32_t>(_mm_movemask_epi8(_mm_cmpeq_epi8(match, ctrl))));
#endif
}
// Returns a bitmask representing the positions of empty or deleted slots.
NonIterableBitMask<uint32_t, kWidth> MaskEmptyOrDeleted() const {
auto special = _mm_set1_epi8(static_cast<char>(ctrl_t::kSentinel));
return NonIterableBitMask<uint32_t, kWidth>(static_cast<uint32_t>(
_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(static_cast<char>(ctrl_t::kSentinel));
return TrailingZeros(static_cast<uint32_t>(
_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);
#ifdef ABSL_INTERNAL_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 // ABSL_INTERNAL_RAW_HASH_SET_HAVE_SSE2
#if defined(ABSL_INTERNAL_HAVE_ARM_NEON) && defined(ABSL_IS_LITTLE_ENDIAN)
struct GroupAArch64Impl {
static constexpr size_t kWidth = 8;
explicit GroupAArch64Impl(const ctrl_t* pos) {
ctrl = vld1_u8(reinterpret_cast<const uint8_t*>(pos));
}
BitMask<uint64_t, kWidth, 3> Match(h2_t hash) const {
uint8x8_t dup = vdup_n_u8(hash);
auto mask = vceq_u8(ctrl, dup);
constexpr uint64_t msbs = 0x8080808080808080ULL;
return BitMask<uint64_t, kWidth, 3>(
vget_lane_u64(vreinterpret_u64_u8(mask), 0) & msbs);
}
NonIterableBitMask<uint64_t, kWidth, 3> MaskEmpty() const {
uint64_t mask =
vget_lane_u64(vreinterpret_u64_u8(vceq_s8(
vdup_n_s8(static_cast<int8_t>(ctrl_t::kEmpty)),
vreinterpret_s8_u8(ctrl))),
0);
return NonIterableBitMask<uint64_t, kWidth, 3>(mask);
}
NonIterableBitMask<uint64_t, kWidth, 3> MaskEmptyOrDeleted() const {
uint64_t mask =
vget_lane_u64(vreinterpret_u64_u8(vcgt_s8(
vdup_n_s8(static_cast<int8_t>(ctrl_t::kSentinel)),
vreinterpret_s8_u8(ctrl))),
0);
return NonIterableBitMask<uint64_t, kWidth, 3>(mask);
}
uint32_t CountLeadingEmptyOrDeleted() const {
uint64_t mask = vget_lane_u64(vreinterpret_u64_u8(ctrl), 0);
// ctrl | ~(ctrl >> 7) will have the lowest bit set to zero for kEmpty and
// kDeleted. We lower all other bits and count number of trailing zeros.
// Clang and GCC optimize countr_zero to rbit+clz without any check for 0,
// so we should be fine.
constexpr uint64_t bits = 0x0101010101010101ULL;
return static_cast<uint32_t>(countr_zero((mask | ~(mask >> 7)) & bits) >>
3);
}
void ConvertSpecialToEmptyAndFullToDeleted(ctrl_t* dst) const {
uint64_t mask = vget_lane_u64(vreinterpret_u64_u8(ctrl), 0);
constexpr uint64_t msbs = 0x8080808080808080ULL;
constexpr uint64_t lsbs = 0x0101010101010101ULL;
auto x = mask & msbs;
auto res = (~x + (x >> 7)) & ~lsbs;
little_endian::Store64(dst, res);
}
uint8x8_t ctrl;
};
#endif // ABSL_INTERNAL_HAVE_ARM_NEON && ABSL_IS_LITTLE_ENDIAN
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 ctrl_t::kEmpty, ctrl_t::kDeleted, ctrl_t::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);
}
NonIterableBitMask<uint64_t, kWidth, 3> MaskEmpty() const {
constexpr uint64_t msbs = 0x8080808080808080ULL;
return NonIterableBitMask<uint64_t, kWidth, 3>((ctrl & (~ctrl << 6)) &
msbs);
}
NonIterableBitMask<uint64_t, kWidth, 3> MaskEmptyOrDeleted() const {
constexpr uint64_t msbs = 0x8080808080808080ULL;
return NonIterableBitMask<uint64_t, kWidth, 3>((ctrl & (~ctrl << 7)) &
msbs);
}
uint32_t CountLeadingEmptyOrDeleted() const {
// ctrl | ~(ctrl >> 7) will have the lowest bit set to zero for kEmpty and
// kDeleted. We lower all other bits and count number of trailing zeros.
constexpr uint64_t bits = 0x0101010101010101ULL;
return static_cast<uint32_t>(countr_zero((ctrl | ~(ctrl >> 7)) & bits) >>
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;
};
#ifdef ABSL_INTERNAL_HAVE_SSE2
using Group = GroupSse2Impl;
#elif defined(ABSL_INTERNAL_HAVE_ARM_NEON) && defined(ABSL_IS_LITTLE_ENDIAN)
using Group = GroupAArch64Impl;
#else
using Group = GroupPortableImpl;
#endif
// CommonFields hold the fields in raw_hash_set that do not depend
// on template parameters. This allows us to conveniently pass all
// of this state to helper functions as a single argument.
//
// We make HashtablezInfoHandle a base class to take advantage of
// the empty base-class optimization when sampling is turned off.
class CommonFields : public HashtablezInfoHandle {
public:
CommonFields() = default;
// Not copyable
CommonFields(const CommonFields&) = delete;
CommonFields& operator=(const CommonFields&) = delete;
// Movable
CommonFields(CommonFields&& that)
: HashtablezInfoHandle(
std::move(static_cast<HashtablezInfoHandle&&>(that))),
// Explicitly copying fields into "this" and then resetting "that"
// fields generates less code then calling absl::exchange per field.
control_(that.control_),
slots_(that.slots_),
size_(that.size_),
capacity_(that.capacity_) {
that.control_ = EmptyGroup();
that.slots_ = nullptr;
that.size_ = 0;
that.capacity_ = 0;
}
CommonFields& operator=(CommonFields&&) = default;
// TODO(b/259599413): Investigate removing some of these fields:
// - control/slots can be derived from each other
// - size can be moved into the slot array
// The control bytes (and, also, a pointer to the base of the backing array).
//
// This contains `capacity + 1 + NumClonedBytes()` entries, even
// when the table is empty (hence EmptyGroup).
ctrl_t* control_ = EmptyGroup();
// The beginning of the slots, located at `SlotOffset()` bytes after
// `control`. May be null for empty tables.
void* slots_ = nullptr;
// The number of filled slots.
size_t size_ = 0;
// The total number of available slots.
size_t capacity_ = 0;
HashtablezInfoHandle& infoz() { return *this; }
const HashtablezInfoHandle& infoz() const { return *this; }
};
// Returns he number of "cloned control bytes".
//
// This is the number of control bytes that are present both at the beginning
// of the control byte array and at the end, such that we can create a
// `Group::kWidth`-width probe window starting from any control byte.
constexpr size_t NumClonedBytes() { return Group::kWidth - 1; }
template <class Policy, class Hash, class Eq, class Alloc>
class raw_hash_set;
// Returns whether `n` is a valid capacity (i.e., number of slots).
//
// A valid capacity is a non-zero integer `2^m - 1`.
inline bool IsValidCapacity(size_t n) { return ((n + 1) & n) == 0 && n > 0; }
// Applies the following mapping to every byte in the control array:
// * kDeleted -> kEmpty
// * kEmpty -> kEmpty
// * _ -> kDeleted
// PRECONDITION:
// IsValidCapacity(capacity)
// ctrl[capacity] == ctrl_t::kSentinel
// ctrl[i] != ctrl_t::kSentinel for all i < capacity
void ConvertDeletedToEmptyAndFullToDeleted(ctrl_t* ctrl, size_t capacity);
// Converts `n` into the next valid capacity, per `IsValidCapacity`.
inline size_t NormalizeCapacity(size_t n) {
return n ? ~size_t{} >> countl_zero(n) : 1;
}
// General notes on capacity/growth methods below:
// - We use 7/8th as maximum load factor. For 16-wide groups, that gives an
// average of two empty slots per group.
// - For (capacity+1) >= Group::kWidth, growth is 7/8*capacity.
// - For (capacity+1) < Group::kWidth, growth == capacity. In this case, we
// never need to probe (the whole table fits in one group) so we don't need a
// load factor less than 1.
// Given `capacity`, applies the load factor; i.e., it returns the maximum
// number of values we should put into the table before a resizing rehash.
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;
}
// Given `growth`, "unapplies" the load factor to find how large the capacity
// should be to stay within the load factor.
//
// This might not be a valid capacity and `NormalizeCapacity()` should be
// called on this.
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);
}
template <class InputIter>
size_t SelectBucketCountForIterRange(InputIter first, InputIter last,
size_t bucket_count) {
if (bucket_count != 0) {
return bucket_count;
}
using InputIterCategory =
typename std::iterator_traits<InputIter>::iterator_category;
if (std::is_base_of<std::random_access_iterator_tag,
InputIterCategory>::value) {
return GrowthToLowerboundCapacity(
static_cast<size_t>(std::distance(first, last)));
}
return 0;
}
#define ABSL_INTERNAL_ASSERT_IS_FULL(ctrl, operation) \
do { \
ABSL_HARDENING_ASSERT( \
(ctrl != nullptr) && operation \
" called on invalid iterator. The iterator might be an end() " \
"iterator or may have been default constructed."); \
ABSL_HARDENING_ASSERT( \
(IsFull(*ctrl)) && operation \
" called on invalid iterator. The element might have been erased or " \
"the table might have rehashed."); \
} while (0)
// Note that for comparisons, null/end iterators are valid.
inline void AssertIsValidForComparison(const ctrl_t* ctrl) {
ABSL_HARDENING_ASSERT((ctrl == nullptr || IsFull(*ctrl)) &&
"Invalid iterator comparison. The element might have "
"been erased or the table might have rehashed.");
}
// If the two iterators come from the same container, then their pointers will
// interleave such that ctrl_a <= ctrl_b < slot_a <= slot_b or vice/versa.
// Note: we take slots by reference so that it's not UB if they're uninitialized
// as long as we don't read them (when ctrl is null).
inline bool AreItersFromSameContainer(const ctrl_t* ctrl_a,
const ctrl_t* ctrl_b,
const void* const& slot_a,
const void* const& slot_b) {
// If either control byte is null, then we can't tell.
if (ctrl_a == nullptr || ctrl_b == nullptr) return true;
const void* low_slot = slot_a;
const void* hi_slot = slot_b;
if (ctrl_a > ctrl_b) {
std::swap(ctrl_a, ctrl_b);
std::swap(low_slot, hi_slot);
}
return ctrl_b < low_slot && low_slot <= hi_slot;
}
// Asserts that two iterators come from the same container.
// Note: we take slots by reference so that it's not UB if they're uninitialized
// as long as we don't read them (when ctrl is null).
inline void AssertSameContainer(const ctrl_t* ctrl_a, const ctrl_t* ctrl_b,
const void* const& slot_a,
const void* const& slot_b) {
ABSL_HARDENING_ASSERT(
AreItersFromSameContainer(ctrl_a, ctrl_b, slot_a, slot_b) &&
"Invalid iterator comparison. The iterators may be from different "
"containers or the container might have rehashed.");
}
struct FindInfo {
size_t offset;
size_t probe_length;
};
// Whether a table is "small". A small table fits entirely into a probing
// group, i.e., has a capacity < `Group::kWidth`.
//
// In small mode we are able to use the whole capacity. The extra control
// bytes give us at least one "empty" control byte to stop the iteration.
// This is important to make 1 a valid capacity.
//
// In small mode only the first `capacity` control bytes after the sentinel
// are valid. The rest contain dummy ctrl_t::kEmpty values that do not
// represent a real slot. This is important to take into account on
// `find_first_non_full()`, where we never try
// `ShouldInsertBackwards()` for small tables.
inline bool is_small(size_t capacity) { return capacity < Group::kWidth - 1; }
// Begins a probing operation on `common.control`, using `hash`.
inline probe_seq<Group::kWidth> probe(const CommonFields& common, size_t hash) {
const ctrl_t* ctrl = common.control_;
const size_t capacity = common.capacity_;
return probe_seq<Group::kWidth>(H1(hash, ctrl), capacity);
}
// Probes an array of control bits using a probe sequence derived from `hash`,
// and returns the offset corresponding to the first deleted or empty slot.
//
// Behavior when the entire table is full is undefined.
//
// NOTE: this function must work with tables having both empty and deleted
// slots in the same group. Such tables appear during `erase()`.
template <typename = void>
inline FindInfo find_first_non_full(const CommonFields& common, size_t hash) {
auto seq = probe(common, hash);
const ctrl_t* ctrl = common.control_;
while (true) {
Group g{ctrl + seq.offset()};
auto mask = g.MaskEmptyOrDeleted();
if (mask) {
#if !defined(NDEBUG)
// We want to add entropy even when ASLR is not enabled.
// 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 (!is_small(common.capacity_) && ShouldInsertBackwards(hash, ctrl)) {
return {seq.offset(mask.HighestBitSet()), seq.index()};
}
#endif
return {seq.offset(mask.LowestBitSet()), seq.index()};
}
seq.next();
assert(seq.index() <= common.capacity_ && "full table!");
}
}
// Extern template for inline function keep possibility of inlining.
// When compiler decided to not inline, no symbols will be added to the
// corresponding translation unit.
extern template FindInfo find_first_non_full(const CommonFields&, size_t);
// Non-inlined version of find_first_non_full for use in less
// performance critical routines.
FindInfo find_first_non_full_outofline(const CommonFields&, size_t);
inline void ResetGrowthLeft(CommonFields& common, size_t& growth_left) {
growth_left = CapacityToGrowth(common.capacity_) - common.size_;
}
// Sets `ctrl` to `{kEmpty, kSentinel, ..., kEmpty}`, marking the entire
// array as marked as empty.
inline void ResetCtrl(CommonFields& common, size_t& growth_left,
size_t slot_size) {
const size_t capacity = common.capacity_;
ctrl_t* ctrl = common.control_;
std::memset(ctrl, static_cast<int8_t>(ctrl_t::kEmpty),
capacity + 1 + NumClonedBytes());
ctrl[capacity] = ctrl_t::kSentinel;
SanitizerPoisonMemoryRegion(common.slots_, slot_size * capacity);
ResetGrowthLeft(common, growth_left);
}
// Sets `ctrl[i]` to `h`.
//
// Unlike setting it directly, this function will perform bounds checks and
// mirror the value to the cloned tail if necessary.
inline void SetCtrl(const CommonFields& common, size_t i, ctrl_t h,
size_t slot_size) {
const size_t capacity = common.capacity_;
assert(i < capacity);
auto* slot_i = static_cast<const char*>(common.slots_) + i * slot_size;
if (IsFull(h)) {
SanitizerUnpoisonMemoryRegion(slot_i, slot_size);
} else {
SanitizerPoisonMemoryRegion(slot_i, slot_size);
}
ctrl_t* ctrl = common.control_;
ctrl[i] = h;
ctrl[((i - NumClonedBytes()) & capacity) + (NumClonedBytes() & capacity)] = h;
}
// Overload for setting to an occupied `h2_t` rather than a special `ctrl_t`.
inline void SetCtrl(const CommonFields& common, size_t i, h2_t h,
size_t slot_size) {
SetCtrl(common, i, static_cast<ctrl_t>(h), slot_size);
}
// Given the capacity of a table, computes the offset (from the start of the
// backing allocation) at which the slots begin.
inline size_t SlotOffset(size_t capacity, size_t slot_align) {
assert(IsValidCapacity(capacity));
const size_t num_control_bytes = capacity + 1 + NumClonedBytes();
return (num_control_bytes + slot_align - 1) & (~slot_align + 1);
}
// Given the capacity of a table, computes the total size of the backing
// array.
inline size_t AllocSize(size_t capacity, size_t slot_size, size_t slot_align) {
return SlotOffset(capacity, slot_align) + capacity * slot_size;
}
template <typename Alloc, size_t SizeOfSlot, size_t AlignOfSlot>
ABSL_ATTRIBUTE_NOINLINE void InitializeSlots(CommonFields& c,
size_t& growth_left, Alloc alloc) {
assert(c.capacity_);
// Folks with custom allocators often make unwarranted assumptions about the
// behavior of their classes vis-a-vis trivial destructability and what
// calls they will or won't make. Avoid sampling for people with custom
// allocators to get us out of this mess. This is not a hard guarantee but
// a workaround while we plan the exact guarantee we want to provide.
const size_t sample_size =
(std::is_same<Alloc, std::allocator<char>>::value && c.slots_ == nullptr)
? SizeOfSlot
: 0;
const size_t cap = c.capacity_;
char* mem = static_cast<char*>(
Allocate<AlignOfSlot>(&alloc, AllocSize(cap, SizeOfSlot, AlignOfSlot)));
c.control_ = reinterpret_cast<ctrl_t*>(mem);
c.slots_ = mem + SlotOffset(cap, AlignOfSlot);
ResetCtrl(c, growth_left, SizeOfSlot);
if (sample_size) {
c.infoz() = Sample(sample_size);
}
c.infoz().RecordStorageChanged(c.size_, cap);
}
// PolicyFunctions bundles together some information for a particular
// raw_hash_set<T, ...> instantiation. This information is passed to
// type-erased functions that want to do small amounts of type-specific
// work.
struct PolicyFunctions {
size_t slot_size;
// Return the hash of the pointed-to slot.
size_t (*hash_slot)(void* set, void* slot);
// Transfer the contents of src_slot to dst_slot.
void (*transfer)(void* set, void* dst_slot, void* src_slot);
// Deallocate the specified backing store which is sized for n slots.
void (*dealloc)(void* set, const PolicyFunctions& policy, ctrl_t* ctrl,
void* slot_array, size_t n);
};
// ClearBackingArray clears the backing array, either modifying it in place,
// or creating a new one based on the value of "reuse".
// REQUIRES: c.capacity > 0
void ClearBackingArray(CommonFields& c, size_t& growth_left,
const PolicyFunctions& policy, bool reuse);
// Type-erased version of raw_hash_set::erase_meta_only.
void EraseMetaOnly(CommonFields& c, size_t& growth_left, ctrl_t* it,
size_t slot_size);
// Function to place in PolicyFunctions::dealloc for raw_hash_sets
// that are using std::allocator. This allows us to share the same
// function body for raw_hash_set instantiations that have the
// same slot alignment.
template <size_t AlignOfSlot>
ABSL_ATTRIBUTE_NOINLINE void DeallocateStandard(void*,
const PolicyFunctions& policy,
ctrl_t* ctrl, void* slot_array,
size_t n) {
// Unpoison before returning the memory to the allocator.
SanitizerUnpoisonMemoryRegion(slot_array, policy.slot_size * n);
std::allocator<char> alloc;
Deallocate<AlignOfSlot>(&alloc, ctrl,
AllocSize(n, policy.slot_size, AlignOfSlot));
}
// For trivially relocatable types we use memcpy directly. This allows us to
// share the same function body for raw_hash_set instantiations that have the
// same slot size as long as they are relocatable.
template <size_t SizeOfSlot>
ABSL_ATTRIBUTE_NOINLINE void TransferRelocatable(void*, void* dst, void* src) {
memcpy(dst, src, SizeOfSlot);
}
// Type-erased version of raw_hash_set::drop_deletes_without_resize.
void DropDeletesWithoutResize(CommonFields& common, size_t& growth_left,
const PolicyFunctions& policy, void* tmp_space);
// A SwissTable.
//
// 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
// [https://en.cppreference.com/w/cpp/named_req/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 : private CommonFields {
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 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 {
ABSL_INTERNAL_ASSERT_IS_FULL(ctrl_, "operator*()");
return PolicyTraits::element(slot_);
}
// PRECONDITION: not an end() iterator.
pointer operator->() const {
ABSL_INTERNAL_ASSERT_IS_FULL(ctrl_, "operator->");
return &operator*();
}
// PRECONDITION: not an end() iterator.
iterator& operator++() {
ABSL_INTERNAL_ASSERT_IS_FULL(ctrl_, "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) {
AssertSameContainer(a.ctrl_, b.ctrl_, a.slot_, b.slot_);
AssertIsValidForComparison(a.ctrl_);
AssertIsValidForComparison(b.ctrl_);
return a.ctrl_ == b.ctrl_;
}
friend bool operator!=(const iterator& a, const iterator& b) {
return !(a == b);
}
private:
iterator(ctrl_t* ctrl, slot_type* slot) : ctrl_(ctrl), slot_(slot) {
// This assumption helps the compiler know that any non-end iterator is
// not equal to any end iterator.
ABSL_ASSUME(ctrl != nullptr);
}
// Fixes up `ctrl_` to point to a full by advancing it and `slot_` until
// they reach one.
//
// If a sentinel is reached, we null `ctrl_` out instead.
void skip_empty_or_deleted() {
while (IsEmptyOrDeleted(*ctrl_)) {
uint32_t shift = Group{ctrl_}.CountLeadingEmptyOrDeleted();
ctrl_ += shift;
slot_ += shift;
}
if (ABSL_PREDICT_FALSE(*ctrl_ == ctrl_t::kSentinel)) ctrl_ = nullptr;
}
ctrl_t* ctrl_ = nullptr;
// To avoid uninitialized member warnings, 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) {}
ABSL_ATTRIBUTE_NOINLINE explicit raw_hash_set(
size_t bucket_count, const hasher& hash = hasher(),
const key_equal& eq = key_equal(),
const allocator_type& alloc = allocator_type())
: settings_(0u, hash, eq, alloc) {
if (bucket_count) {
common().capacity_ = NormalizeCapacity(bucket_count);
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(SelectBucketCountForIterRange(first, last, 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_outofline(common(), hash);
SetCtrl(common(), target.offset, H2(hash), sizeof(slot_type));
emplace_at(target.offset, v);
infoz().RecordInsert(hash, target.probe_length);
}
common().size_ = that.size();
growth_left() -= that.size();
}
ABSL_ATTRIBUTE_NOINLINE 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)
: // 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.
CommonFields(std::move(that)),
settings_(absl::exchange(that.growth_left(), size_t{0}),
that.hash_ref(), that.eq_ref(), that.alloc_ref()) {}
raw_hash_set(raw_hash_set&& that, const allocator_type& a)
: settings_(0, that.hash_ref(), that.eq_ref(), a) {
if (a == that.alloc_ref()) {
std::swap(common(), that.common());
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() {
const size_t cap = capacity();
if (!cap) return;
destroy_slots();
// Unpoison before returning the memory to the allocator.
SanitizerUnpoisonMemoryRegion(slot_array(), sizeof(slot_type) * cap);
Deallocate<alignof(slot_type)>(
&alloc_ref(), control(),
AllocSize(cap, sizeof(slot_type), alignof(slot_type)));
infoz().Unregister();
}
iterator begin() {
auto it = iterator_at(0);
it.skip_empty_or_deleted();
return it;
}
iterator end() { return {}; }
const_iterator begin() const {
return const_cast<raw_hash_set*>(this)->begin();
}
const_iterator end() const { return {}; }
const_iterator cbegin() const { return begin(); }
const_iterator cend() const { return end(); }
bool empty() const { return !size(); }
size_t size() const { return common().size_; }
size_t capacity() const { return common().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.
const size_t cap = capacity();
if (cap == 0) {
// Already guaranteed to be empty; so nothing to do.
} else {
destroy_slots();
ClearBackingArray(common(), growth_left(), GetPolicyFunctions(),
/*reuse=*/cap < 128);
}
}
inline void destroy_slots() {
const size_t cap = capacity();
const ctrl_t* ctrl = control();
slot_type* slot = slot_array();
for (size_t i = 0; i != cap; ++i) {
if (IsFull(ctrl[i])) {
PolicyTraits::destroy(&alloc_ref(), slot + i);
}
}
}
// 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));
// TODO(cheshire): A type alias T2 is introduced as a workaround for the nvcc
// bug.
template <class T, RequiresInsertable<T> = 0, class T2 = T,
typename std::enable_if<IsDecomposable<T2>::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_map<std::string, int> s;
// s.insert({"abc", 42});
std::pair<iterator, bool> insert(init_type&& value) {
return emplace(std::move(value));
}
// TODO(cheshire): A type alias T2 is introduced as a workaround for the nvcc
// bug.
template <class T, RequiresInsertable<T> = 0, class T2 = T,
typename std::enable_if<IsDecomposable<T2>::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) emplace(*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) {
auto res = insert(std::move(node));
node = std::move(res.node);
return res.position;
}
// 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) {
alignas(slot_type) unsigned char raw[sizeof(slot_type)];
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 abide by several restrictions:
// - it MUST call `raw_hash_set::constructor` with arguments as if a
// `raw_hash_set::value_type` is constructed,
// - it MUST NOT access the container before the call to
// `raw_hash_set::constructor`, and
// - it MUST NOT erase the lazily emplaced element.
// Doing any of these is undefined behavior.
//
// 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 = slot_array() + 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). The
// iterator is invalidated, so any increment should be done before calling
// erase. 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;) {
// // `erase()` will invalidate `it`, so advance `it` first.
// auto copy_it = it++;
// if (<pred>) {
// m.erase(copy_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) {
ABSL_INTERNAL_ASSERT_IS_FULL(it.ctrl_, "erase()");
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;) {
auto next = std::next(it);
if (PolicyTraits::apply(InsertSlot<false>{*this, std::move(*it.slot_)},
PolicyTraits::element(it.slot_))
.second) {
src.erase_meta_only(it);
}
it = next;
}
}
template <typename H, typename E>
void merge(raw_hash_set<Policy, H, E, Alloc>&& src) {
merge(src);
}
node_type extract(const_iterator position) {
ABSL_INTERNAL_ASSERT_IS_FULL(position.inner_.ctrl_, "extract()");
auto node =
CommonAccess::Transfer<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>() &&
IsNoThrowSwappable<allocator_type>(
typename AllocTraits::propagate_on_container_swap{})) {
using std::swap;
swap(common(), that.common());
swap(growth_left(), that.growth_left());
swap(hash_ref(), that.hash_ref());
swap(eq_ref(), that.eq_ref());
SwapAlloc(alloc_ref(), that.alloc_ref(),
typename AllocTraits::propagate_on_container_swap{});
}
void rehash(size_t n) {
if (n == 0 && capacity() == 0) return;
if (n == 0 && size() == 0) {
ClearBackingArray(common(), growth_left(), GetPolicyFunctions(),
/*reuse=*/false);
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);
// This is after resize, to ensure that we have completed the allocation
// and have potentially sampled the hashtable.
infoz().RecordReservation(n);
}
}
void reserve(size_t n) {
if (n > size() + growth_left()) {
size_t m = GrowthToLowerboundCapacity(n);
resize(NormalizeCapacity(m));
// This is after resize, to ensure that we have completed the allocation
// and have potentially sampled the hashtable.
infoz().RecordReservation(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;
// Avoid probing if we won't be able to prefetch the addresses received.
#ifdef ABSL_INTERNAL_HAVE_PREFETCH
prefetch_heap_block();
auto seq = probe(common(), hash_ref()(key));
base_internal::PrefetchT0(control() + seq.offset());
base_internal::PrefetchT0(slot_array() + seq.offset());
#endif // ABSL_INTERNAL_HAVE_PREFETCH
}
// 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(common(), hash);
slot_type* slot_ptr = slot_array();
const ctrl_t* ctrl = control();
while (true) {
Group g{ctrl + seq.offset()};
for (uint32_t i : g.Match(H2(hash))) {
if (ABSL_PREDICT_TRUE(PolicyTraits::apply(
EqualElement<K>{key, eq_ref()},
PolicyTraits::element(slot_ptr + seq.offset(i)))))
return iterator_at(seq.offset(i));
}
if (ABSL_PREDICT_TRUE(g.MaskEmpty())) return end();
seq.next();
assert(seq.index() <= capacity() && "full table!");
}
}
template <class K = key_type>
iterator find(const key_arg<K>& key) {
prefetch_heap_block();
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 {
prefetch_heap_block();
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);
}
template <typename H>
friend typename std::enable_if<H::template is_hashable<value_type>::value,
H>::type
AbslHashValue(H h, const raw_hash_set& s) {
return H::combine(H::combine_unordered(std::move(h), s.begin(), s.end()),
s.size());
}
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.slot_array() + 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, but does not destroy, the value pointed to by `it`.
//
// This merely updates the pertinent control byte. This can be used in
// conjunction with Policy::transfer to move the object to another place.
void erase_meta_only(const_iterator it) {
EraseMetaOnly(common(), growth_left(), it.inner_.ctrl_, sizeof(slot_type));
}
// Allocates a backing array for `self` and initializes its control bytes.
// This reads `capacity` and updates all other fields based on the result of
// the allocation.
//
// This does not free the currently held array; `capacity` must be nonzero.
inline void initialize_slots() {
// People are often sloppy with the exact type of their allocator (sometimes
// it has an extra const or is missing the pair, but rebinds made it work
// anyway).
using CharAlloc =
typename absl::allocator_traits<Alloc>::template rebind_alloc<char>;
InitializeSlots<CharAlloc, sizeof(slot_type), alignof(slot_type)>(
common(), growth_left(), CharAlloc(alloc_ref()));
}
ABSL_ATTRIBUTE_NOINLINE void resize(size_t new_capacity) {
assert(IsValidCapacity(new_capacity));
auto* old_ctrl = control();
auto* old_slots = slot_array();
const size_t old_capacity = common().capacity_;
common().capacity_ = new_capacity;
initialize_slots();
auto* new_slots = slot_array();
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(common(), hash);
size_t new_i = target.offset;
total_probe_length += target.probe_length;
SetCtrl(common(), new_i, H2(hash), sizeof(slot_type));
PolicyTraits::transfer(&alloc_ref(), new_slots + new_i, old_slots + i);
}
}
if (old_capacity) {
SanitizerUnpoisonMemoryRegion(old_slots,
sizeof(slot_type) * old_capacity);
Deallocate<alignof(slot_type)>(
&alloc_ref(), old_ctrl,
AllocSize(old_capacity, sizeof(slot_type), alignof(slot_type)));
}
infoz().RecordRehash(total_probe_length);
}
// Prunes control bytes to remove as many tombstones as possible.
//
// See the comment on `rehash_and_grow_if_necessary()`.
inline void drop_deletes_without_resize() {
// Stack-allocate space for swapping elements.
alignas(slot_type) unsigned char tmp[sizeof(slot_type)];
DropDeletesWithoutResize(common(), growth_left(), GetPolicyFunctions(),
tmp);
}
// Called whenever the table *might* need to conditionally grow.
//
// This function is an optimization opportunity to perform a rehash even when
// growth is unnecessary, because vacating tombstones is beneficial for
// performance in the long-run.
void rehash_and_grow_if_necessary() {
const size_t cap = capacity();
if (cap > Group::kWidth &&
// Do these calcuations in 64-bit to avoid overflow.
size() * uint64_t{32} <= cap* uint64_t{25}) {
// Squash DELETED without growing if there is enough capacity.
//
// Rehash in place if the current size is <= 25/32 of capacity.
// Rationale for such a high factor: 1) drop_deletes_without_resize() is
// faster than resize, and 2) it takes quite a bit of work to add
// tombstones. In the worst case, seems to take approximately 4
// insert/erase pairs to create a single tombstone and so if we are
// rehashing because of tombstones, we can afford to rehash-in-place as
// long as we are reclaiming at least 1/8 the capacity without doing more
// than 2X the work. (Where "work" is defined to be size() for rehashing
// or rehashing in place, and 1 for an insert or erase.) But rehashing in
// place is faster per operation than inserting or even doubling the size
// of the table, so we actually afford to reclaim even less space from a
// resize-in-place. The decision is to rehash in place if we can reclaim
// at about 1/8th of the usable capacity (specifically 3/28 of the
// capacity) which means that the total cost of rehashing will be a small
// fraction of the total work.
//
// Here is output of an experiment using the BM_CacheInSteadyState
// benchmark running the old case (where we rehash-in-place only if we can
// reclaim at least 7/16*capacity) vs. this code (which rehashes in place
// if we can recover 3/32*capacity).
//
// Note that although in the worst-case number of rehashes jumped up from
// 15 to 190, but the number of operations per second is almost the same.
//
// Abridged output of running BM_CacheInSteadyState benchmark from
// raw_hash_set_benchmark. N is the number of insert/erase operations.
//
// | OLD (recover >= 7/16 | NEW (recover >= 3/32)
// size | N/s LoadFactor NRehashes | N/s LoadFactor NRehashes
// 448 | 145284 0.44 18 | 140118 0.44 19
// 493 | 152546 0.24 11 | 151417 0.48 28
// 538 | 151439 0.26 11 | 151152 0.53 38
// 583 | 151765 0.28 11 | 150572 0.57 50
// 628 | 150241 0.31 11 | 150853 0.61 66
// 672 | 149602 0.33 12 | 150110 0.66 90
// 717 | 149998 0.35 12 | 149531 0.70 129
// 762 | 149836 0.37 13 | 148559 0.74 190
// 807 | 149736 0.39 14 | 151107 0.39 14
// 852 | 150204 0.42 15 | 151019 0.42 15
drop_deletes_without_resize();
} else {
// Otherwise grow the container.
resize(cap * 2 + 1);
}
}
bool has_element(const value_type& elem) const {
size_t hash = PolicyTraits::apply(HashElement{hash_ref()}, elem);
auto seq = probe(common(), hash);
const ctrl_t* ctrl = control();
while (true) {
Group g{ctrl + seq.offset()};
for (uint32_t i : g.Match(H2(hash))) {
if (ABSL_PREDICT_TRUE(
PolicyTraits::element(slot_array() + seq.offset(i)) == elem))
return true;
}
if (ABSL_PREDICT_TRUE(g.MaskEmpty())) return false;
seq.next();
assert(seq.index() <= capacity() && "full table!");
}
return false;
}
// 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:
// Attempts to find `key` in the table; if it isn't found, returns a slot that
// the value can be inserted into, with the control byte already set to
// `key`'s H2.
template <class K>
std::pair<size_t, bool> find_or_prepare_insert(const K& key) {
prefetch_heap_block();
auto hash = hash_ref()(key);
auto seq = probe(common(), hash);
const ctrl_t* ctrl = control();
while (true) {
Group g{ctrl + seq.offset()};
for (uint32_t i : g.Match(H2(hash))) {
if (ABSL_PREDICT_TRUE(PolicyTraits::apply(
EqualElement<K>{key, eq_ref()},
PolicyTraits::element(slot_array() + seq.offset(i)))))
return {seq.offset(i), false};
}
if (ABSL_PREDICT_TRUE(g.MaskEmpty())) break;
seq.next();
assert(seq.index() <= capacity() && "full table!");
}
return {prepare_insert(hash), true};
}
// Given the hash of a value not currently in the table, finds the next
// viable slot index to insert it at.
//
// REQUIRES: At least one non-full slot available.
size_t prepare_insert(size_t hash) ABSL_ATTRIBUTE_NOINLINE {
auto target = find_first_non_full(common(), hash);
if (ABSL_PREDICT_FALSE(growth_left() == 0 &&
!IsDeleted(control()[target.offset]))) {
rehash_and_grow_if_necessary();
target = find_first_non_full(common(), hash);
}
++common().size_;
growth_left() -= IsEmpty(control()[target.offset]);
SetCtrl(common(), target.offset, H2(hash), sizeof(slot_type));
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(), slot_array() + 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 {control() + i, slot_array() + i}; }
const_iterator iterator_at(size_t i) const {
return {control() + i, slot_array() + i};
}
private:
friend struct RawHashSetTestOnlyAccess;
// The number of slots we can still fill without needing to rehash.
//
// This is stored separately due to tombstones: we do not include tombstones
// in the growth capacity, because we'd like to rehash when the table is
// otherwise filled with tombstones: otherwise, probe sequences might get
// unacceptably long without triggering a rehash. Callers can also force a
// rehash via the standard `rehash(0)`, which will recompute this value as a
// side-effect.
//
// See `CapacityToGrowth()`.
size_t& growth_left() { return settings_.template get<0>(); }
// Prefetch the heap-allocated memory region to resolve potential TLB misses.
// This is intended to overlap with execution of calculating the hash for a
// key.
void prefetch_heap_block() const { base_internal::PrefetchT2(control()); }
CommonFields& common() { return *this; }
const CommonFields& common() const { return *this; }
ctrl_t* control() const { return common().control_; }
slot_type* slot_array() const {
return static_cast<slot_type*>(common().slots_);
}
HashtablezInfoHandle& infoz() { return common().infoz(); }
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>();
}
// Make type-specific functions for this type's PolicyFunctions struct.
static size_t hash_slot_fn(void* set, void* slot) {
auto* h = static_cast<raw_hash_set*>(set);
return PolicyTraits::apply(
HashElement{h->hash_ref()},
PolicyTraits::element(static_cast<slot_type*>(slot)));
}
static void transfer_slot_fn(void* set, void* dst, void* src) {
auto* h = static_cast<raw_hash_set*>(set);
PolicyTraits::transfer(&h->alloc_ref(), static_cast<slot_type*>(dst),
static_cast<slot_type*>(src));
}
// Note: dealloc_fn will only be used if we have a non-standard allocator.
static void dealloc_fn(void* set, const PolicyFunctions&, ctrl_t* ctrl,
void* slot_mem, size_t n) {
auto* h = static_cast<raw_hash_set*>(set);
// Unpoison before returning the memory to the allocator.
SanitizerUnpoisonMemoryRegion(slot_mem, sizeof(slot_type) * n);
Deallocate<alignof(slot_type)>(
&h->alloc_ref(), ctrl,
AllocSize(n, sizeof(slot_type), alignof(slot_type)));
}
static const PolicyFunctions& GetPolicyFunctions() {
static constexpr PolicyFunctions value = {
sizeof(slot_type),
&raw_hash_set::hash_slot_fn,
PolicyTraits::transfer_uses_memcpy()
? TransferRelocatable<sizeof(slot_type)>
: &raw_hash_set::transfer_slot_fn,
(std::is_same<SlotAlloc, std::allocator<slot_type>>::value
? &DeallocateStandard<alignof(slot_type)>
: &raw_hash_set::dealloc_fn),
};
return value;
}
// Bundle together growth_left (number of slots that can be filled without
// rehashing) plus other objects which might be empty. CompressedTuple will
// ensure that sizeof is not affected by any of the empty fields that occur
// after growth_left.
absl::container_internal::CompressedTuple<size_t /* growth_left */, hasher,
key_equal, allocator_type>
settings_{0u, hasher{}, key_equal{}, allocator_type{}};
};
// Erases all elements that satisfy the predicate `pred` from the container `c`.
template <typename P, typename H, typename E, typename A, typename Predicate>
typename raw_hash_set<P, H, E, A>::size_type EraseIf(
Predicate& pred, raw_hash_set<P, H, E, A>* c) {
const auto initial_size = c->size();
for (auto it = c->begin(), last = c->end(); it != last;) {
if (pred(*it)) {
c->erase(it++);
} else {
++it;
}
}
return initial_size - c->size();
}
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 = probe(set.common(), hash);
const ctrl_t* ctrl = set.control();
while (true) {
container_internal::Group g{ctrl + seq.offset()};
for (uint32_t 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.slot_array() + seq.offset(i))))
return num_probes;
++num_probes;
}
if (g.MaskEmpty()) return num_probes;
seq.next();
++num_probes;
}
}
static size_t AllocatedByteSize(const Set& c) {
size_t capacity = c.capacity();
if (capacity == 0) return 0;
size_t m = AllocSize(capacity, sizeof(Slot), alignof(Slot));
size_t per_slot = Traits::space_used(static_cast<const Slot*>(nullptr));
if (per_slot != ~size_t{}) {
m += per_slot * c.size();
} else {
const ctrl_t* ctrl = c.control();
for (size_t i = 0; i != capacity; ++i) {
if (container_internal::IsFull(ctrl[i])) {
m += Traits::space_used(c.slot_array() + i);
}
}
}
return m;
}
static size_t LowerBoundAllocatedByteSize(size_t size) {
size_t capacity = GrowthToLowerboundCapacity(size);
if (capacity == 0) return 0;
size_t m =
AllocSize(NormalizeCapacity(capacity), sizeof(Slot), alignof(Slot));
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
ABSL_NAMESPACE_END
} // namespace absl
#undef ABSL_INTERNAL_ASSERT_IS_FULL
#endif // ABSL_CONTAINER_INTERNAL_RAW_HASH_SET_H_