use crate::alloc::alloc::{alloc, dealloc, handle_alloc_error};
use crate::scopeguard::guard;
use crate::CollectionAllocErr;
use core::alloc::Layout;
use core::hint;
use core::iter::FusedIterator;
use core::marker::PhantomData;
use core::mem;
use core::mem::ManuallyDrop;
use core::ptr::NonNull;
cfg_if! {
// Use the SSE2 implementation if possible: it allows us to scan 16 buckets
// at once instead of 8. We don't bother with AVX since it would require
// runtime dispatch and wouldn't gain us much anyways: the probability of
// finding a match drops off drastically after the first few buckets.
//
// I attempted an implementation on ARM using NEON instructions, but it
// turns out that most NEON instructions have multi-cycle latency, which in
// the end outweighs any gains over the generic implementation.
if #[cfg(all(
target_feature = "sse2",
any(target_arch = "x86", target_arch = "x86_64"),
not(miri)
))] {
mod sse2;
use sse2 as imp;
} else {
#[path = "generic.rs"]
mod generic;
use generic as imp;
}
}
mod bitmask;
use self::bitmask::BitMask;
use self::imp::Group;
// Branch prediction hint. This is currently only available on nightly but it
// consistently improves performance by 10-15%.
#[cfg(feature = "nightly")]
use core::intrinsics::{likely, unlikely};
#[cfg(not(feature = "nightly"))]
#[inline]
fn likely(b: bool) -> bool {
b
}
#[cfg(not(feature = "nightly"))]
#[inline]
fn unlikely(b: bool) -> bool {
b
}
#[cfg(feature = "nightly")]
#[cfg_attr(feature = "inline-more", inline)]
unsafe fn offset_from<T>(to: *const T, from: *const T) -> usize {
to.offset_from(from) as usize
}
#[cfg(not(feature = "nightly"))]
#[cfg_attr(feature = "inline-more", inline)]
unsafe fn offset_from<T>(to: *const T, from: *const T) -> usize {
(to as usize - from as usize) / mem::size_of::<T>()
}
/// Whether memory allocation errors should return an error or abort.
#[derive(Copy, Clone)]
enum Fallibility {
Fallible,
Infallible,
}
impl Fallibility {
/// Error to return on capacity overflow.
#[cfg_attr(feature = "inline-more", inline)]
fn capacity_overflow(self) -> CollectionAllocErr {
match self {
Fallibility::Fallible => CollectionAllocErr::CapacityOverflow,
Fallibility::Infallible => panic!("Hash table capacity overflow"),
}
}
/// Error to return on allocation error.
#[cfg_attr(feature = "inline-more", inline)]
fn alloc_err(self, layout: Layout) -> CollectionAllocErr {
match self {
Fallibility::Fallible => CollectionAllocErr::AllocErr { layout },
Fallibility::Infallible => handle_alloc_error(layout),
}
}
}
/// Control byte value for an empty bucket.
const EMPTY: u8 = 0b1111_1111;
/// Control byte value for a deleted bucket.
const DELETED: u8 = 0b1000_0000;
/// Checks whether a control byte represents a full bucket (top bit is clear).
#[inline]
fn is_full(ctrl: u8) -> bool {
ctrl & 0x80 == 0
}
/// Checks whether a control byte represents a special value (top bit is set).
#[inline]
fn is_special(ctrl: u8) -> bool {
ctrl & 0x80 != 0
}
/// Checks whether a special control value is EMPTY (just check 1 bit).
#[inline]
fn special_is_empty(ctrl: u8) -> bool {
debug_assert!(is_special(ctrl));
ctrl & 0x01 != 0
}
/// Primary hash function, used to select the initial bucket to probe from.
#[inline]
#[allow(clippy::cast_possible_truncation)]
fn h1(hash: u64) -> usize {
// On 32-bit platforms we simply ignore the higher hash bits.
hash as usize
}
/// Secondary hash function, saved in the low 7 bits of the control byte.
#[inline]
#[allow(clippy::cast_possible_truncation)]
fn h2(hash: u64) -> u8 {
// Grab the top 7 bits of the hash. While the hash is normally a full 64-bit
// value, some hash functions (such as FxHash) produce a usize result
// instead, which means that the top 32 bits are 0 on 32-bit platforms.
let hash_len = usize::min(mem::size_of::<usize>(), mem::size_of::<u64>());
let top7 = hash >> (hash_len * 8 - 7);
(top7 & 0x7f) as u8 // truncation
}
/// Probe sequence based on triangular numbers, which is guaranteed (since our
/// table size is a power of two) to visit every group of elements exactly once.
///
/// A triangular probe has us jump by 1 more group every time. So first we
/// jump by 1 group (meaning we just continue our linear scan), then 2 groups
/// (skipping over 1 group), then 3 groups (skipping over 2 groups), and so on.
///
/// Proof that the probe will visit every group in the table:
/// <https://fgiesen.wordpress.com/2015/02/22/triangular-numbers-mod-2n/>
struct ProbeSeq {
bucket_mask: usize,
pos: usize,
stride: usize,
}
impl Iterator for ProbeSeq {
type Item = usize;
#[inline]
fn next(&mut self) -> Option<usize> {
// We should have found an empty bucket by now and ended the probe.
debug_assert!(
self.stride <= self.bucket_mask,
"Went past end of probe sequence"
);
let result = self.pos;
self.stride += Group::WIDTH;
self.pos += self.stride;
self.pos &= self.bucket_mask;
Some(result)
}
}
/// Returns the number of buckets needed to hold the given number of items,
/// taking the maximum load factor into account.
///
/// Returns `None` if an overflow occurs.
#[cfg_attr(feature = "inline-more", inline)]
// Workaround for emscripten bug emscripten-core/emscripten-fastcomp#258
#[cfg_attr(target_os = "emscripten", inline(never))]
fn capacity_to_buckets(cap: usize) -> Option<usize> {
let adjusted_cap = if cap < 8 {
// Need at least 1 free bucket on small tables
cap + 1
} else {
// Otherwise require 1/8 buckets to be empty (87.5% load)
//
// Be careful when modifying this, calculate_layout relies on the
// overflow check here.
cap.checked_mul(8)? / 7
};
// Any overflows will have been caught by the checked_mul. Also, any
// rounding errors from the division above will be cleaned up by
// next_power_of_two (which can't overflow because of the previous divison).
Some(adjusted_cap.next_power_of_two())
}
/// Returns the maximum effective capacity for the given bucket mask, taking
/// the maximum load factor into account.
#[cfg_attr(feature = "inline-more", inline)]
fn bucket_mask_to_capacity(bucket_mask: usize) -> usize {
if bucket_mask < 8 {
// For tables with 1/2/4/8 buckets, we always reserve one empty slot.
// Keep in mind that the bucket mask is one less than the bucket count.
bucket_mask
} else {
// For larger tables we reserve 12.5% of the slots as empty.
((bucket_mask + 1) / 8) * 7
}
}
// Returns a Layout which describes the allocation required for a hash table,
// and the offset of the buckets in the allocation.
///
/// Returns `None` if an overflow occurs.
#[cfg_attr(feature = "inline-more", inline)]
#[cfg(feature = "nightly")]
fn calculate_layout<T>(buckets: usize) -> Option<(Layout, usize)> {
debug_assert!(buckets.is_power_of_two());
// Array of buckets
let data = Layout::array::<T>(buckets).ok()?;
// Array of control bytes. This must be aligned to the group size.
//
// We add `Group::WIDTH` control bytes at the end of the array which
// replicate the bytes at the start of the array and thus avoids the need to
// perform bounds-checking while probing.
//
// There is no possible overflow here since buckets is a power of two and
// Group::WIDTH is a small number.
let ctrl = unsafe { Layout::from_size_align_unchecked(buckets + Group::WIDTH, Group::WIDTH) };
ctrl.extend(data).ok()
}
// Returns a Layout which describes the allocation required for a hash table,
// and the offset of the buckets in the allocation.
#[cfg_attr(feature = "inline-more", inline)]
#[cfg(not(feature = "nightly"))]
fn calculate_layout<T>(buckets: usize) -> Option<(Layout, usize)> {
debug_assert!(buckets.is_power_of_two());
// Manual layout calculation since Layout methods are not yet stable.
let data_align = usize::max(mem::align_of::<T>(), Group::WIDTH);
let data_offset = (buckets + Group::WIDTH).checked_add(data_align - 1)? & !(data_align - 1);
let len = data_offset.checked_add(mem::size_of::<T>().checked_mul(buckets)?)?;
Some((
unsafe { Layout::from_size_align_unchecked(len, data_align) },
data_offset,
))
}
/// A reference to a hash table bucket containing a `T`.
///
/// This is usually just a pointer to the element itself. However if the element
/// is a ZST, then we instead track the index of the element in the table so
/// that `erase` works properly.
pub struct Bucket<T> {
// Using *const for variance
ptr: *const T,
}
// This Send impl is needed for rayon support. This is safe since Bucket is
// never exposed in a public API.
unsafe impl<T> Send for Bucket<T> {}
impl<T> Clone for Bucket<T> {
#[cfg_attr(feature = "inline-more", inline)]
fn clone(&self) -> Self {
Self { ptr: self.ptr }
}
}
impl<T> Bucket<T> {
#[cfg_attr(feature = "inline-more", inline)]
unsafe fn from_base_index(base: *const T, index: usize) -> Self {
let ptr = if mem::size_of::<T>() == 0 {
index as *const T
} else {
base.add(index)
};
Self { ptr }
}
#[cfg_attr(feature = "inline-more", inline)]
pub unsafe fn as_ptr(&self) -> *mut T {
if mem::size_of::<T>() == 0 {
// Just return an arbitrary ZST pointer which is properly aligned
mem::align_of::<T>() as *mut T
} else {
self.ptr as *mut T
}
}
#[cfg_attr(feature = "inline-more", inline)]
unsafe fn add(&self, offset: usize) -> Self {
let ptr = if mem::size_of::<T>() == 0 {
(self.ptr as usize + offset) as *const T
} else {
self.ptr.add(offset)
};
Self { ptr }
}
#[cfg_attr(feature = "inline-more", inline)]
pub unsafe fn drop(&self) {
self.as_ptr().drop_in_place();
}
#[cfg_attr(feature = "inline-more", inline)]
pub unsafe fn read(&self) -> T {
self.as_ptr().read()
}
#[cfg_attr(feature = "inline-more", inline)]
pub unsafe fn write(&self, val: T) {
self.as_ptr().write(val);
}
#[cfg_attr(feature = "inline-more", inline)]
pub unsafe fn as_ref<'a>(&self) -> &'a T {
&*self.as_ptr()
}
#[cfg_attr(feature = "inline-more", inline)]
pub unsafe fn as_mut<'a>(&self) -> &'a mut T {
&mut *self.as_ptr()
}
#[cfg_attr(feature = "inline-more", inline)]
pub unsafe fn copy_from_nonoverlapping(&self, other: &Self) {
self.as_ptr().copy_from_nonoverlapping(other.as_ptr(), 1);
}
}
/// A raw hash table with an unsafe API.
pub struct RawTable<T> {
// Mask to get an index from a hash value. The value is one less than the
// number of buckets in the table.
bucket_mask: usize,
// Pointer to the array of control bytes
ctrl: NonNull<u8>,
// Pointer to the array of buckets
data: NonNull<T>,
// Number of elements that can be inserted before we need to grow the table
growth_left: usize,
// Number of elements in the table, only really used by len()
items: usize,
// Tell dropck that we own instances of T.
marker: PhantomData<T>,
}
impl<T> RawTable<T> {
/// Creates a new empty hash table without allocating any memory.
///
/// In effect this returns a table with exactly 1 bucket. However we can
/// leave the data pointer dangling since that bucket is never written to
/// due to our load factor forcing us to always have at least 1 free bucket.
#[cfg_attr(feature = "inline-more", inline)]
pub fn new() -> Self {
Self {
data: NonNull::dangling(),
// Be careful to cast the entire slice to a raw pointer.
ctrl: unsafe { NonNull::new_unchecked(Group::static_empty().as_ptr() as *mut u8) },
bucket_mask: 0,
items: 0,
growth_left: 0,
marker: PhantomData,
}
}
/// Allocates a new hash table with the given number of buckets.
///
/// The control bytes are left uninitialized.
#[cfg_attr(feature = "inline-more", inline)]
unsafe fn new_uninitialized(
buckets: usize,
fallability: Fallibility,
) -> Result<Self, CollectionAllocErr> {
debug_assert!(buckets.is_power_of_two());
let (layout, data_offset) =
calculate_layout::<T>(buckets).ok_or_else(|| fallability.capacity_overflow())?;
let ctrl = NonNull::new(alloc(layout)).ok_or_else(|| fallability.alloc_err(layout))?;
let data = NonNull::new_unchecked(ctrl.as_ptr().add(data_offset) as *mut T);
Ok(Self {
data,
ctrl,
bucket_mask: buckets - 1,
items: 0,
growth_left: bucket_mask_to_capacity(buckets - 1),
marker: PhantomData,
})
}
/// Attempts to allocate a new hash table with at least enough capacity
/// for inserting the given number of elements without reallocating.
fn try_with_capacity(
capacity: usize,
fallability: Fallibility,
) -> Result<Self, CollectionAllocErr> {
if capacity == 0 {
Ok(Self::new())
} else {
unsafe {
let buckets =
capacity_to_buckets(capacity).ok_or_else(|| fallability.capacity_overflow())?;
let result = Self::new_uninitialized(buckets, fallability)?;
result.ctrl(0).write_bytes(EMPTY, result.num_ctrl_bytes());
Ok(result)
}
}
}
/// Allocates a new hash table with at least enough capacity for inserting
/// the given number of elements without reallocating.
pub fn with_capacity(capacity: usize) -> Self {
Self::try_with_capacity(capacity, Fallibility::Infallible)
.unwrap_or_else(|_| unsafe { hint::unreachable_unchecked() })
}
/// Deallocates the table without dropping any entries.
#[cfg_attr(feature = "inline-more", inline)]
unsafe fn free_buckets(&mut self) {
let (layout, _) =
calculate_layout::<T>(self.buckets()).unwrap_or_else(|| hint::unreachable_unchecked());
dealloc(self.ctrl.as_ptr(), layout);
}
/// Returns the index of a bucket from a `Bucket`.
#[cfg_attr(feature = "inline-more", inline)]
pub unsafe fn bucket_index(&self, bucket: &Bucket<T>) -> usize {
if mem::size_of::<T>() == 0 {
bucket.ptr as usize
} else {
offset_from(bucket.ptr, self.data.as_ptr())
}
}
/// Returns a pointer to a control byte.
#[cfg_attr(feature = "inline-more", inline)]
unsafe fn ctrl(&self, index: usize) -> *mut u8 {
debug_assert!(index < self.num_ctrl_bytes());
self.ctrl.as_ptr().add(index)
}
/// Returns a pointer to an element in the table.
#[cfg_attr(feature = "inline-more", inline)]
pub unsafe fn bucket(&self, index: usize) -> Bucket<T> {
debug_assert_ne!(self.bucket_mask, 0);
debug_assert!(index < self.buckets());
Bucket::from_base_index(self.data.as_ptr(), index)
}
/// Erases an element from the table without dropping it.
#[cfg_attr(feature = "inline-more", inline)]
pub unsafe fn erase_no_drop(&mut self, item: &Bucket<T>) {
let index = self.bucket_index(item);
debug_assert!(is_full(*self.ctrl(index)));
let index_before = index.wrapping_sub(Group::WIDTH) & self.bucket_mask;
let empty_before = Group::load(self.ctrl(index_before)).match_empty();
let empty_after = Group::load(self.ctrl(index)).match_empty();
// If we are inside a continuous block of Group::WIDTH full or deleted
// cells then a probe window may have seen a full block when trying to
// insert. We therefore need to keep that block non-empty so that
// lookups will continue searching to the next probe window.
//
// Note that in this context `leading_zeros` refers to the bytes at the
// end of a group, while `trailing_zeros` refers to the bytes at the
// begining of a group.
let ctrl = if empty_before.leading_zeros() + empty_after.trailing_zeros() >= Group::WIDTH {
DELETED
} else {
self.growth_left += 1;
EMPTY
};
self.set_ctrl(index, ctrl);
self.items -= 1;
}
/// Returns an iterator for a probe sequence on the table.
///
/// This iterator never terminates, but is guaranteed to visit each bucket
/// group exactly once. The loop using `probe_seq` must terminate upon
/// reaching a group containing an empty bucket.
#[cfg_attr(feature = "inline-more", inline)]
fn probe_seq(&self, hash: u64) -> ProbeSeq {
ProbeSeq {
bucket_mask: self.bucket_mask,
pos: h1(hash) & self.bucket_mask,
stride: 0,
}
}
/// Sets a control byte, and possibly also the replicated control byte at
/// the end of the array.
#[cfg_attr(feature = "inline-more", inline)]
unsafe fn set_ctrl(&self, index: usize, ctrl: u8) {
// Replicate the first Group::WIDTH control bytes at the end of
// the array without using a branch:
// - If index >= Group::WIDTH then index == index2.
// - Otherwise index2 == self.bucket_mask + 1 + index.
//
// The very last replicated control byte is never actually read because
// we mask the initial index for unaligned loads, but we write it
// anyways because it makes the set_ctrl implementation simpler.
//
// If there are fewer buckets than Group::WIDTH then this code will
// replicate the buckets at the end of the trailing group. For example
// with 2 buckets and a group size of 4, the control bytes will look
// like this:
//
// Real | Replicated
// ---------------------------------------------
// | [A] | [B] | [EMPTY] | [EMPTY] | [A] | [B] |
// ---------------------------------------------
let index2 = ((index.wrapping_sub(Group::WIDTH)) & self.bucket_mask) + Group::WIDTH;
*self.ctrl(index) = ctrl;
*self.ctrl(index2) = ctrl;
}
/// Searches for an empty or deleted bucket which is suitable for inserting
/// a new element.
///
/// There must be at least 1 empty bucket in the table.
#[cfg_attr(feature = "inline-more", inline)]
fn find_insert_slot(&self, hash: u64) -> usize {
for pos in self.probe_seq(hash) {
unsafe {
let group = Group::load(self.ctrl(pos));
if let Some(bit) = group.match_empty_or_deleted().lowest_set_bit() {
let result = (pos + bit) & self.bucket_mask;
// In tables smaller than the group width, trailing control
// bytes outside the range of the table are filled with
// EMPTY entries. These will unfortunately trigger a
// match, but once masked may point to a full bucket that
// is already occupied. We detect this situation here and
// perform a second scan starting at the begining of the
// table. This second scan is guaranteed to find an empty
// slot (due to the load factor) before hitting the trailing
// control bytes (containing EMPTY).
if unlikely(is_full(*self.ctrl(result))) {
debug_assert!(self.bucket_mask < Group::WIDTH);
debug_assert_ne!(pos, 0);
return Group::load_aligned(self.ctrl(0))
.match_empty_or_deleted()
.lowest_set_bit_nonzero();
} else {
return result;
}
}
}
}
// probe_seq never returns.
unreachable!();
}
/// Marks all table buckets as empty without dropping their contents.
#[cfg_attr(feature = "inline-more", inline)]
pub fn clear_no_drop(&mut self) {
if !self.is_empty_singleton() {
unsafe {
self.ctrl(0).write_bytes(EMPTY, self.num_ctrl_bytes());
}
}
self.items = 0;
self.growth_left = bucket_mask_to_capacity(self.bucket_mask);
}
/// Removes all elements from the table without freeing the backing memory.
#[cfg_attr(feature = "inline-more", inline)]
pub fn clear(&mut self) {
// Ensure that the table is reset even if one of the drops panic
let self_ = guard(self, |self_| self_.clear_no_drop());
if mem::needs_drop::<T>() {
unsafe {
for item in self_.iter() {
item.drop();
}
}
}
}
/// Shrinks the table to fit `max(self.len(), min_size)` elements.
#[cfg_attr(feature = "inline-more", inline)]
pub fn shrink_to(&mut self, min_size: usize, hasher: impl Fn(&T) -> u64) {
// Calculate the minimal number of elements that we need to reserve
// space for.
let min_size = usize::max(self.items, min_size);
if min_size == 0 {
*self = Self::new();
return;
}
// Calculate the number of buckets that we need for this number of
// elements. If the calculation overflows then the requested bucket
// count must be larger than what we have right and nothing needs to be
// done.
let min_buckets = match capacity_to_buckets(min_size) {
Some(buckets) => buckets,
None => return,
};
// If we have more buckets than we need, shrink the table.
if min_buckets < self.buckets() {
// Fast path if the table is empty
if self.items == 0 {
*self = Self::with_capacity(min_size)
} else {
self.resize(min_size, hasher, Fallibility::Infallible)
.unwrap_or_else(|_| unsafe { hint::unreachable_unchecked() });
}
}
}
/// Ensures that at least `additional` items can be inserted into the table
/// without reallocation.
#[cfg_attr(feature = "inline-more", inline)]
pub fn reserve(&mut self, additional: usize, hasher: impl Fn(&T) -> u64) {
if additional > self.growth_left {
self.reserve_rehash(additional, hasher, Fallibility::Infallible)
.unwrap_or_else(|_| unsafe { hint::unreachable_unchecked() });
}
}
/// Tries to ensure that at least `additional` items can be inserted into
/// the table without reallocation.
#[cfg_attr(feature = "inline-more", inline)]
pub fn try_reserve(
&mut self,
additional: usize,
hasher: impl Fn(&T) -> u64,
) -> Result<(), CollectionAllocErr> {
if additional > self.growth_left {
self.reserve_rehash(additional, hasher, Fallibility::Fallible)
} else {
Ok(())
}
}
/// Out-of-line slow path for `reserve` and `try_reserve`.
#[cold]
#[inline(never)]
fn reserve_rehash(
&mut self,
additional: usize,
hasher: impl Fn(&T) -> u64,
fallability: Fallibility,
) -> Result<(), CollectionAllocErr> {
let new_items = self
.items
.checked_add(additional)
.ok_or_else(|| fallability.capacity_overflow())?;
let full_capacity = bucket_mask_to_capacity(self.bucket_mask);
if new_items <= full_capacity / 2 {
// Rehash in-place without re-allocating if we have plenty of spare
// capacity that is locked up due to DELETED entries.
self.rehash_in_place(hasher);
Ok(())
} else {
// Otherwise, conservatively resize to at least the next size up
// to avoid churning deletes into frequent rehashes.
self.resize(
usize::max(new_items, full_capacity + 1),
hasher,
fallability,
)
}
}
/// Rehashes the contents of the table in place (i.e. without changing the
/// allocation).
///
/// If `hasher` panics then some the table's contents may be lost.
fn rehash_in_place(&mut self, hasher: impl Fn(&T) -> u64) {
unsafe {
// Bulk convert all full control bytes to DELETED, and all DELETED
// control bytes to EMPTY. This effectively frees up all buckets
// containing a DELETED entry.
for i in (0..self.buckets()).step_by(Group::WIDTH) {
let group = Group::load_aligned(self.ctrl(i));
let group = group.convert_special_to_empty_and_full_to_deleted();
group.store_aligned(self.ctrl(i));
}
// Fix up the trailing control bytes. See the comments in set_ctrl
// for the handling of tables smaller than the group width.
if self.buckets() < Group::WIDTH {
self.ctrl(0)
.copy_to(self.ctrl(Group::WIDTH), self.buckets());
} else {
self.ctrl(0)
.copy_to(self.ctrl(self.buckets()), Group::WIDTH);
}
// If the hash function panics then properly clean up any elements
// that we haven't rehashed yet. We unfortunately can't preserve the
// element since we lost their hash and have no way of recovering it
// without risking another panic.
let mut guard = guard(self, |self_| {
if mem::needs_drop::<T>() {
for i in 0..self_.buckets() {
if *self_.ctrl(i) == DELETED {
self_.set_ctrl(i, EMPTY);
self_.bucket(i).drop();
self_.items -= 1;
}
}
}
self_.growth_left = bucket_mask_to_capacity(self_.bucket_mask) - self_.items;
});
// At this point, DELETED elements are elements that we haven't
// rehashed yet. Find them and re-insert them at their ideal
// position.
'outer: for i in 0..guard.buckets() {
if *guard.ctrl(i) != DELETED {
continue;
}
'inner: loop {
// Hash the current item
let item = guard.bucket(i);
let hash = hasher(item.as_ref());
// Search for a suitable place to put it
let new_i = guard.find_insert_slot(hash);
// Probing works by scanning through all of the control
// bytes in groups, which may not be aligned to the group
// size. If both the new and old position fall within the
// same unaligned group, then there is no benefit in moving
// it and we can just continue to the next item.
let probe_index = |pos: usize| {
(pos.wrapping_sub(guard.probe_seq(hash).pos) & guard.bucket_mask)
/ Group::WIDTH
};
if likely(probe_index(i) == probe_index(new_i)) {
guard.set_ctrl(i, h2(hash));
continue 'outer;
}
// We are moving the current item to a new position. Write
// our H2 to the control byte of the new position.
let prev_ctrl = *guard.ctrl(new_i);
guard.set_ctrl(new_i, h2(hash));
if prev_ctrl == EMPTY {
// If the target slot is empty, simply move the current
// element into the new slot and clear the old control
// byte.
guard.set_ctrl(i, EMPTY);
guard.bucket(new_i).copy_from_nonoverlapping(&item);
continue 'outer;
} else {
// If the target slot is occupied, swap the two elements
// and then continue processing the element that we just
// swapped into the old slot.
debug_assert_eq!(prev_ctrl, DELETED);
mem::swap(guard.bucket(new_i).as_mut(), item.as_mut());
continue 'inner;
}
}
}
guard.growth_left = bucket_mask_to_capacity(guard.bucket_mask) - guard.items;
mem::forget(guard);
}
}
/// Allocates a new table of a different size and moves the contents of the
/// current table into it.
fn resize(
&mut self,
capacity: usize,
hasher: impl Fn(&T) -> u64,
fallability: Fallibility,
) -> Result<(), CollectionAllocErr> {
unsafe {
debug_assert!(self.items <= capacity);
// Allocate and initialize the new table.
let mut new_table = Self::try_with_capacity(capacity, fallability)?;
new_table.growth_left -= self.items;
new_table.items = self.items;
// The hash function may panic, in which case we simply free the new
// table without dropping any elements that may have been copied into
// it.
//
// This guard is also used to free the old table on success, see
// the comment at the bottom of this function.
let mut new_table = guard(ManuallyDrop::new(new_table), |new_table| {
if !new_table.is_empty_singleton() {
new_table.free_buckets();
}
});
// Copy all elements to the new table.
for item in self.iter() {
// This may panic.
let hash = hasher(item.as_ref());
// We can use a simpler version of insert() here since:
// - there are no DELETED entries.
// - we know there is enough space in the table.
// - all elements are unique.
let index = new_table.find_insert_slot(hash);
new_table.set_ctrl(index, h2(hash));
new_table.bucket(index).copy_from_nonoverlapping(&item);
}
// We successfully copied all elements without panicking. Now replace
// self with the new table. The old table will have its memory freed but
// the items will not be dropped (since they have been moved into the
// new table).
mem::swap(self, &mut new_table);
Ok(())
}
}
/// Inserts a new element into the table.
///
/// This does not check if the given element already exists in the table.
#[cfg_attr(feature = "inline-more", inline)]
pub fn insert(&mut self, hash: u64, value: T, hasher: impl Fn(&T) -> u64) -> Bucket<T> {
unsafe {
let mut index = self.find_insert_slot(hash);
// We can avoid growing the table once we have reached our load
// factor if we are replacing a tombstone. This works since the
// number of EMPTY slots does not change in this case.
let old_ctrl = *self.ctrl(index);
if unlikely(self.growth_left == 0 && special_is_empty(old_ctrl)) {
self.reserve(1, hasher);
index = self.find_insert_slot(hash);
}
let bucket = self.bucket(index);
self.growth_left -= special_is_empty(old_ctrl) as usize;
self.set_ctrl(index, h2(hash));
bucket.write(value);
self.items += 1;
bucket
}
}
/// Inserts a new element into the table, without growing the table.
///
/// There must be enough space in the table to insert the new element.
///
/// This does not check if the given element already exists in the table.
#[cfg_attr(feature = "inline-more", inline)]
#[cfg(feature = "rustc-internal-api")]
pub fn insert_no_grow(&mut self, hash: u64, value: T) -> Bucket<T> {
unsafe {
let index = self.find_insert_slot(hash);
let bucket = self.bucket(index);
// If we are replacing a DELETED entry then we don't need to update
// the load counter.
let old_ctrl = *self.ctrl(index);
self.growth_left -= special_is_empty(old_ctrl) as usize;
self.set_ctrl(index, h2(hash));
bucket.write(value);
self.items += 1;
bucket
}
}
/// Searches for an element in the table.
#[inline]
pub fn find(&self, hash: u64, mut eq: impl FnMut(&T) -> bool) -> Option<Bucket<T>> {
unsafe {
for pos in self.probe_seq(hash) {
let group = Group::load(self.ctrl(pos));
for bit in group.match_byte(h2(hash)) {
let index = (pos + bit) & self.bucket_mask;
let bucket = self.bucket(index);
if likely(eq(bucket.as_ref())) {
return Some(bucket);
}
}
if likely(group.match_empty().any_bit_set()) {
return None;
}
}
}
// probe_seq never returns.
unreachable!();
}
/// Returns the number of elements the map can hold without reallocating.
///
/// This number is a lower bound; the table might be able to hold
/// more, but is guaranteed to be able to hold at least this many.
#[cfg_attr(feature = "inline-more", inline)]
pub fn capacity(&self) -> usize {
self.items + self.growth_left
}
/// Returns the number of elements in the table.
#[cfg_attr(feature = "inline-more", inline)]
pub fn len(&self) -> usize {
self.items
}
/// Returns the number of buckets in the table.
#[cfg_attr(feature = "inline-more", inline)]
pub fn buckets(&self) -> usize {
self.bucket_mask + 1
}
/// Returns the number of control bytes in the table.
#[cfg_attr(feature = "inline-more", inline)]
fn num_ctrl_bytes(&self) -> usize {
self.bucket_mask + 1 + Group::WIDTH
}
/// Returns whether this table points to the empty singleton with a capacity
/// of 0.
#[cfg_attr(feature = "inline-more", inline)]
fn is_empty_singleton(&self) -> bool {
self.bucket_mask == 0
}
/// Returns an iterator over every element in the table. It is up to
/// the caller to ensure that the `RawTable` outlives the `RawIter`.
/// Because we cannot make the `next` method unsafe on the `RawIter`
/// struct, we have to make the `iter` method unsafe.
#[cfg_attr(feature = "inline-more", inline)]
pub unsafe fn iter(&self) -> RawIter<T> {
let data = Bucket::from_base_index(self.data.as_ptr(), 0);
RawIter {
iter: RawIterRange::new(self.ctrl.as_ptr(), data, self.buckets()),
items: self.items,
}
}
/// Returns an iterator which removes all elements from the table without
/// freeing the memory. It is up to the caller to ensure that the `RawTable`
/// outlives the `RawDrain`. Because we cannot make the `next` method unsafe
/// on the `RawDrain`, we have to make the `drain` method unsafe.
#[cfg_attr(feature = "inline-more", inline)]
pub unsafe fn drain(&mut self) -> RawDrain<'_, T> {
RawDrain {
iter: self.iter(),
table: ManuallyDrop::new(mem::replace(self, Self::new())),
orig_table: NonNull::from(self),
marker: PhantomData,
}
}
/// Converts the table into a raw allocation. The contents of the table
/// should be dropped using a `RawIter` before freeing the allocation.
#[cfg_attr(feature = "inline-more", inline)]
pub(crate) fn into_alloc(self) -> Option<(NonNull<u8>, Layout)> {
let alloc = if self.is_empty_singleton() {
None
} else {
let (layout, _) = calculate_layout::<T>(self.buckets())
.unwrap_or_else(|| unsafe { hint::unreachable_unchecked() });
Some((self.ctrl.cast(), layout))
};
mem::forget(self);
alloc
}
}
unsafe impl<T> Send for RawTable<T> where T: Send {}
unsafe impl<T> Sync for RawTable<T> where T: Sync {}
impl<T: Clone> Clone for RawTable<T> {
fn clone(&self) -> Self {
if self.is_empty_singleton() {
Self::new()
} else {
unsafe {
let mut new_table = ManuallyDrop::new(
Self::new_uninitialized(self.buckets(), Fallibility::Infallible)
.unwrap_or_else(|_| hint::unreachable_unchecked()),
);
new_table.clone_from_spec(self, |new_table| {
// We need to free the memory allocated for the new table.
new_table.free_buckets();
});
// Return the newly created table.
ManuallyDrop::into_inner(new_table)
}
}
}
fn clone_from(&mut self, source: &Self) {
if source.is_empty_singleton() {
*self = Self::new();
} else {
unsafe {
// First, drop all our elements without clearing the control bytes.
if mem::needs_drop::<T>() {
for item in self.iter() {
item.drop();
}
}
// If necessary, resize our table to match the source.
if self.buckets() != source.buckets() {
// Skip our drop by using ptr::write.
if !self.is_empty_singleton() {
self.free_buckets();
}
(self as *mut Self).write(
Self::new_uninitialized(source.buckets(), Fallibility::Infallible)
.unwrap_or_else(|_| hint::unreachable_unchecked()),
);
}
self.clone_from_spec(source, |self_| {
// We need to leave the table in an empty state.
self_.clear_no_drop()
});
}
}
}
}
/// Specialization of `clone_from` for `Copy` types
trait RawTableClone {
unsafe fn clone_from_spec(&mut self, source: &Self, on_panic: impl FnMut(&mut Self));
}
impl<T: Clone> RawTableClone for RawTable<T> {
#[cfg(feature = "nightly")]
#[cfg_attr(feature = "inline-more", inline)]
default unsafe fn clone_from_spec(&mut self, source: &Self, on_panic: impl FnMut(&mut Self)) {
self.clone_from_impl(source, on_panic);
}
#[cfg(not(feature = "nightly"))]
#[cfg_attr(feature = "inline-more", inline)]
unsafe fn clone_from_spec(&mut self, source: &Self, on_panic: impl FnMut(&mut Self)) {
self.clone_from_impl(source, on_panic);
}
}
#[cfg(feature = "nightly")]
impl<T: Copy> RawTableClone for RawTable<T> {
#[cfg_attr(feature = "inline-more", inline)]
unsafe fn clone_from_spec(&mut self, source: &Self, _on_panic: impl FnMut(&mut Self)) {
source
.ctrl(0)
.copy_to_nonoverlapping(self.ctrl(0), self.num_ctrl_bytes());
source
.data
.as_ptr()
.copy_to_nonoverlapping(self.data.as_ptr(), self.buckets());
self.items = source.items;
self.growth_left = source.growth_left;
}
}
impl<T: Clone> RawTable<T> {
/// Common code for clone and clone_from. Assumes `self.buckets() == source.buckets()`.
#[cfg_attr(feature = "inline-more", inline)]
unsafe fn clone_from_impl(&mut self, source: &Self, mut on_panic: impl FnMut(&mut Self)) {
// Copy the control bytes unchanged. We do this in a single pass
source
.ctrl(0)
.copy_to_nonoverlapping(self.ctrl(0), self.num_ctrl_bytes());
// The cloning of elements may panic, in which case we need
// to make sure we drop only the elements that have been
// cloned so far.
let mut guard = guard((0, &mut *self), |(index, self_)| {
if mem::needs_drop::<T>() {
for i in 0..=*index {
if is_full(*self_.ctrl(i)) {
self_.bucket(i).drop();
}
}
}
// Depending on whether we were called from clone or clone_from, we
// either need to free the memory for the destination table or just
// clear the control bytes.
on_panic(self_);
});
for from in source.iter() {
let index = source.bucket_index(&from);
let to = guard.1.bucket(index);
to.write(from.as_ref().clone());
// Update the index in case we need to unwind.
guard.0 = index;
}
// Successfully cloned all items, no need to clean up.
mem::forget(guard);
self.items = source.items;
self.growth_left = source.growth_left;
}
/// Variant of `clone_from` to use when a hasher is available.
#[cfg(any(feature = "nightly", feature = "raw"))]
pub fn clone_from_with_hasher(&mut self, source: &Self, hasher: impl Fn(&T) -> u64) {
// If we have enough capacity in the table, just clear it and insert
// elements one by one. We don't do this if we have the same number of
// buckets as the source since we can just copy the contents directly
// in that case.
if self.buckets() != source.buckets()
&& bucket_mask_to_capacity(self.bucket_mask) >= source.len()
{
self.clear();
let guard_self = guard(&mut *self, |self_| {
// Clear the partially copied table if a panic occurs, otherwise
// items and growth_left will be out of sync with the contents
// of the table.
self_.clear();
});
unsafe {
for item in source.iter() {
// This may panic.
let item = item.as_ref().clone();
let hash = hasher(&item);
// We can use a simpler version of insert() here since:
// - there are no DELETED entries.
// - we know there is enough space in the table.
// - all elements are unique.
let index = guard_self.find_insert_slot(hash);
guard_self.set_ctrl(index, h2(hash));
guard_self.bucket(index).write(item);
}
}
// Successfully cloned all items, no need to clean up.
mem::forget(guard_self);
self.items = source.items;
self.growth_left -= source.items;
} else {
self.clone_from(source);
}
}
}
#[cfg(feature = "nightly")]
unsafe impl<#[may_dangle] T> Drop for RawTable<T> {
#[cfg_attr(feature = "inline-more", inline)]
fn drop(&mut self) {
if !self.is_empty_singleton() {
unsafe {
if mem::needs_drop::<T>() {
for item in self.iter() {
item.drop();
}
}
self.free_buckets();
}
}
}
}
#[cfg(not(feature = "nightly"))]
impl<T> Drop for RawTable<T> {
#[cfg_attr(feature = "inline-more", inline)]
fn drop(&mut self) {
if !self.is_empty_singleton() {
unsafe {
if mem::needs_drop::<T>() {
for item in self.iter() {
item.drop();
}
}
self.free_buckets();
}
}
}
}
impl<T> IntoIterator for RawTable<T> {
type Item = T;
type IntoIter = RawIntoIter<T>;
#[cfg_attr(feature = "inline-more", inline)]
fn into_iter(self) -> RawIntoIter<T> {
unsafe {
let iter = self.iter();
let alloc = self.into_alloc();
RawIntoIter {
iter,
alloc,
marker: PhantomData,
}
}
}
}
/// Iterator over a sub-range of a table. Unlike `RawIter` this iterator does
/// not track an item count.
pub(crate) struct RawIterRange<T> {
// Mask of full buckets in the current group. Bits are cleared from this
// mask as each element is processed.
current_group: BitMask,
// Pointer to the buckets for the current group.
data: Bucket<T>,
// Pointer to the next group of control bytes,
// Must be aligned to the group size.
next_ctrl: *const u8,
// Pointer one past the last control byte of this range.
end: *const u8,
}
impl<T> RawIterRange<T> {
/// Returns a `RawIterRange` covering a subset of a table.
///
/// The control byte address must be aligned to the group size.
#[cfg_attr(feature = "inline-more", inline)]
unsafe fn new(ctrl: *const u8, data: Bucket<T>, len: usize) -> Self {
debug_assert_ne!(len, 0);
debug_assert_eq!(ctrl as usize % Group::WIDTH, 0);
let end = ctrl.add(len);
// Load the first group and advance ctrl to point to the next group
let current_group = Group::load_aligned(ctrl).match_full();
let next_ctrl = ctrl.add(Group::WIDTH);
Self {
current_group,
data,
next_ctrl,
end,
}
}
/// Splits a `RawIterRange` into two halves.
///
/// Returns `None` if the remaining range is smaller than or equal to the
/// group width.
#[cfg_attr(feature = "inline-more", inline)]
#[cfg(feature = "rayon")]
pub(crate) fn split(mut self) -> (Self, Option<RawIterRange<T>>) {
unsafe {
if self.end <= self.next_ctrl {
// Nothing to split if the group that we are current processing
// is the last one.
(self, None)
} else {
// len is the remaining number of elements after the group that
// we are currently processing. It must be a multiple of the
// group size (small tables are caught by the check above).
let len = offset_from(self.end, self.next_ctrl);
debug_assert_eq!(len % Group::WIDTH, 0);
// Split the remaining elements into two halves, but round the
// midpoint down in case there is an odd number of groups
// remaining. This ensures that:
// - The tail is at least 1 group long.
// - The split is roughly even considering we still have the
// current group to process.
let mid = (len / 2) & !(Group::WIDTH - 1);
let tail = Self::new(
self.next_ctrl.add(mid),
self.data.add(Group::WIDTH).add(mid),
len - mid,
);
debug_assert_eq!(self.data.add(Group::WIDTH).add(mid).ptr, tail.data.ptr);
debug_assert_eq!(self.end, tail.end);
self.end = self.next_ctrl.add(mid);
debug_assert_eq!(self.end.add(Group::WIDTH), tail.next_ctrl);
(self, Some(tail))
}
}
}
}
// We make raw iterators unconditionally Send and Sync, and let the PhantomData
// in the actual iterator implementations determine the real Send/Sync bounds.
unsafe impl<T> Send for RawIterRange<T> {}
unsafe impl<T> Sync for RawIterRange<T> {}
impl<T> Clone for RawIterRange<T> {
#[cfg_attr(feature = "inline-more", inline)]
fn clone(&self) -> Self {
Self {
data: self.data.clone(),
next_ctrl: self.next_ctrl,
current_group: self.current_group,
end: self.end,
}
}
}
impl<T> Iterator for RawIterRange<T> {
type Item = Bucket<T>;
#[cfg_attr(feature = "inline-more", inline)]
fn next(&mut self) -> Option<Bucket<T>> {
unsafe {
loop {
if let Some(index) = self.current_group.lowest_set_bit() {
self.current_group = self.current_group.remove_lowest_bit();
return Some(self.data.add(index));
}
if self.next_ctrl >= self.end {
return None;
}
// We might read past self.end up to the next group boundary,
// but this is fine because it only occurs on tables smaller
// than the group size where the trailing control bytes are all
// EMPTY. On larger tables self.end is guaranteed to be aligned
// to the group size (since tables are power-of-two sized).
self.current_group = Group::load_aligned(self.next_ctrl).match_full();
self.data = self.data.add(Group::WIDTH);
self.next_ctrl = self.next_ctrl.add(Group::WIDTH);
}
}
}
#[cfg_attr(feature = "inline-more", inline)]
fn size_hint(&self) -> (usize, Option<usize>) {
// We don't have an item count, so just guess based on the range size.
(
0,
Some(unsafe { offset_from(self.end, self.next_ctrl) + Group::WIDTH }),
)
}
}
impl<T> FusedIterator for RawIterRange<T> {}
/// Iterator which returns a raw pointer to every full bucket in the table.
pub struct RawIter<T> {
pub(crate) iter: RawIterRange<T>,
items: usize,
}
impl<T> Clone for RawIter<T> {
#[cfg_attr(feature = "inline-more", inline)]
fn clone(&self) -> Self {
Self {
iter: self.iter.clone(),
items: self.items,
}
}
}
impl<T> Iterator for RawIter<T> {
type Item = Bucket<T>;
#[cfg_attr(feature = "inline-more", inline)]
fn next(&mut self) -> Option<Bucket<T>> {
if let Some(b) = self.iter.next() {
self.items -= 1;
Some(b)
} else {
// We don't check against items == 0 here to allow the
// compiler to optimize away the item count entirely if the
// iterator length is never queried.
debug_assert_eq!(self.items, 0);
None
}
}
#[cfg_attr(feature = "inline-more", inline)]
fn size_hint(&self) -> (usize, Option<usize>) {
(self.items, Some(self.items))
}
}
impl<T> ExactSizeIterator for RawIter<T> {}
impl<T> FusedIterator for RawIter<T> {}
/// Iterator which consumes a table and returns elements.
pub struct RawIntoIter<T> {
iter: RawIter<T>,
alloc: Option<(NonNull<u8>, Layout)>,
marker: PhantomData<T>,
}
impl<T> RawIntoIter<T> {
#[cfg_attr(feature = "inline-more", inline)]
pub fn iter(&self) -> RawIter<T> {
self.iter.clone()
}
}
unsafe impl<T> Send for RawIntoIter<T> where T: Send {}
unsafe impl<T> Sync for RawIntoIter<T> where T: Sync {}
#[cfg(feature = "nightly")]
unsafe impl<#[may_dangle] T> Drop for RawIntoIter<T> {
#[cfg_attr(feature = "inline-more", inline)]
fn drop(&mut self) {
unsafe {
// Drop all remaining elements
if mem::needs_drop::<T>() {
while let Some(item) = self.iter.next() {
item.drop();
}
}
// Free the table
if let Some((ptr, layout)) = self.alloc {
dealloc(ptr.as_ptr(), layout);
}
}
}
}
#[cfg(not(feature = "nightly"))]
impl<T> Drop for RawIntoIter<T> {
#[cfg_attr(feature = "inline-more", inline)]
fn drop(&mut self) {
unsafe {
// Drop all remaining elements
if mem::needs_drop::<T>() {
while let Some(item) = self.iter.next() {
item.drop();
}
}
// Free the table
if let Some((ptr, layout)) = self.alloc {
dealloc(ptr.as_ptr(), layout);
}
}
}
}
impl<T> Iterator for RawIntoIter<T> {
type Item = T;
#[cfg_attr(feature = "inline-more", inline)]
fn next(&mut self) -> Option<T> {
unsafe { Some(self.iter.next()?.read()) }
}
#[cfg_attr(feature = "inline-more", inline)]
fn size_hint(&self) -> (usize, Option<usize>) {
self.iter.size_hint()
}
}
impl<T> ExactSizeIterator for RawIntoIter<T> {}
impl<T> FusedIterator for RawIntoIter<T> {}
/// Iterator which consumes elements without freeing the table storage.
pub struct RawDrain<'a, T> {
iter: RawIter<T>,
// The table is moved into the iterator for the duration of the drain. This
// ensures that an empty table is left if the drain iterator is leaked
// without dropping.
table: ManuallyDrop<RawTable<T>>,
orig_table: NonNull<RawTable<T>>,
// We don't use a &'a mut RawTable<T> because we want RawDrain to be
// covariant over T.
marker: PhantomData<&'a RawTable<T>>,
}
impl<T> RawDrain<'_, T> {
#[cfg_attr(feature = "inline-more", inline)]
pub fn iter(&self) -> RawIter<T> {
self.iter.clone()
}
}
unsafe impl<T> Send for RawDrain<'_, T> where T: Send {}
unsafe impl<T> Sync for RawDrain<'_, T> where T: Sync {}
impl<T> Drop for RawDrain<'_, T> {
#[cfg_attr(feature = "inline-more", inline)]
fn drop(&mut self) {
unsafe {
// Drop all remaining elements. Note that this may panic.
if mem::needs_drop::<T>() {
while let Some(item) = self.iter.next() {
item.drop();
}
}
// Reset the contents of the table now that all elements have been
// dropped.
self.table.clear_no_drop();
// Move the now empty table back to its original location.
self.orig_table
.as_ptr()
.copy_from_nonoverlapping(&*self.table, 1);
}
}
}
impl<T> Iterator for RawDrain<'_, T> {
type Item = T;
#[cfg_attr(feature = "inline-more", inline)]
fn next(&mut self) -> Option<T> {
unsafe {
let item = self.iter.next()?;
Some(item.read())
}
}
#[cfg_attr(feature = "inline-more", inline)]
fn size_hint(&self) -> (usize, Option<usize>) {
self.iter.size_hint()
}
}
impl<T> ExactSizeIterator for RawDrain<'_, T> {}
impl<T> FusedIterator for RawDrain<'_, T> {}