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Replace StaticVec with SmallVec.

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This commit is contained in:
Stephen Chung
2020-07-29 16:10:06 +08:00
parent 40850e6b1e
commit afbcd0fc0b
7 changed files with 54 additions and 587 deletions
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555
src/utils.rs
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@@ -1,8 +1,4 @@
//! Module containing various utility types and functions.
//!
//! # Safety
//!
//! The `StaticVec` type has some `unsafe` blocks to handle conversions between `MaybeUninit` and regular types.
use crate::fn_native::{shared_make_mut, shared_take, Shared};
@@ -13,12 +9,9 @@ use crate::stdlib::{
fmt,
hash::{BuildHasher, Hash, Hasher},
iter::FromIterator,
mem,
mem::MaybeUninit,
ops::{Add, AddAssign, Deref, DerefMut, Drop, Index, IndexMut},
ops::{Add, AddAssign, Deref},
str::FromStr,
string::{String, ToString},
vec::Vec,
};
#[cfg(not(feature = "no_std"))]
@@ -27,6 +20,8 @@ use crate::stdlib::collections::hash_map::DefaultHasher;
#[cfg(feature = "no_std")]
use ahash::AHasher;
use smallvec::SmallVec;
/// A hasher that only takes one single `u64` and returns it as a hash key.
///
/// # Panics
@@ -92,549 +87,7 @@ pub fn calc_fn_spec<'a>(
s.finish()
}
/// [INTERNALS] An array-like type that holds a number of values in static storage for no-allocation, quick access.
/// Exported under the `internals` feature only.
///
/// If too many items are stored, it converts into using a `Vec`.
///
///
/// This is essentially a knock-off of the [`staticvec`](https://crates.io/crates/staticvec) crate.
/// This simplified implementation here is to avoid pulling in another crate.
///
/// # Implementation
///
/// A `StaticVec` holds data in _either one_ of two storages: 1) a fixed-size array of `MAX_STATIC_VEC`
/// items, and 2) a dynamic `Vec`. At any time, either one of them (or both) must be empty, depending on the
/// total number of items.
///
/// There is a `len` field containing the total number of items held by the `StaticVec`.
///
/// The fixed-size array (`list`) is not initialized (i.e. initialized with `MaybeUninit::uninit()`).
///
/// When `len <= MAX_STATIC_VEC`, all elements are stored in the fixed-size array.
/// Array slots `>= len` are `MaybeUninit::uninit()` while slots `< len` are considered actual data.
/// In this scenario, the `Vec` (`more`) is empty.
///
/// As soon as we try to push a new item into the `StaticVec` that makes the total number exceed
/// `MAX_STATIC_VEC`, all the items in the fixed-sized array are taken out, replaced with
/// `MaybeUninit::uninit()` (via `mem::replace`) and pushed into the `Vec`.
/// Then the new item is added to the `Vec`.
///
/// Therefore, if `len > MAX_STATIC_VEC`, then the fixed-size array (`list`) is considered
/// empty and uninitialized while all data resides in the `Vec` (`more`).
///
/// When popping an item off of the `StaticVec`, the reverse is true. When `len = MAX_STATIC_VEC + 1`,
/// after popping the item, all the items residing in the `Vec` are moved back to the fixed-size array (`list`).
/// The `Vec` will then be empty.
///
/// Therefore, if `len <= MAX_STATIC_VEC`, data is in the fixed-size array (`list`).
/// Otherwise, data is in the `Vec` (`more`).
///
/// # Safety
///
/// This type uses some unsafe code (mainly for uninitialized/unused array slots) for efficiency.
///
/// ## WARNING
///
/// This type is volatile and may change.
//
// TODO - remove unsafe code
pub struct StaticVec<T> {
/// Total number of values held.
len: usize,
/// Fixed-size storage for fast, no-allocation access.
list: [MaybeUninit<T>; MAX_STATIC_VEC],
/// Dynamic storage. For spill-overs.
more: Vec<T>,
}
/// Maximum slots of fixed-size storage for a `StaticVec`.
/// 4 slots should be enough for most cases.
const MAX_STATIC_VEC: usize = 4;
impl<T> Drop for StaticVec<T> {
fn drop(&mut self) {
self.clear();
}
}
impl<T: Hash> Hash for StaticVec<T> {
fn hash<H: Hasher>(&self, state: &mut H) {
self.iter().for_each(|x| x.hash(state));
}
}
impl<T> Default for StaticVec<T> {
fn default() -> Self {
Self {
len: 0,
list: unsafe { mem::MaybeUninit::uninit().assume_init() },
more: Vec::new(),
}
}
}
impl<T: PartialEq> PartialEq for StaticVec<T> {
fn eq(&self, other: &Self) -> bool {
if self.len != other.len || self.more != other.more {
return false;
}
if self.len > MAX_STATIC_VEC {
return true;
}
unsafe {
mem::transmute::<_, &[T; MAX_STATIC_VEC]>(&self.list)
== mem::transmute::<_, &[T; MAX_STATIC_VEC]>(&other.list)
}
}
}
impl<T: Clone> Clone for StaticVec<T> {
fn clone(&self) -> Self {
let mut value: Self = Default::default();
value.len = self.len;
if self.is_fixed_storage() {
for x in 0..self.len {
let item = self.list.get(x).unwrap();
let item_value = unsafe { mem::transmute::<_, &T>(item) };
value.list[x] = MaybeUninit::new(item_value.clone());
}
} else {
value.more = self.more.clone();
}
value
}
}
impl<T: Eq> Eq for StaticVec<T> {}
impl<T> FromIterator<T> for StaticVec<T> {
fn from_iter<X: IntoIterator<Item = T>>(iter: X) -> Self {
let mut vec = StaticVec::new();
for x in iter {
vec.push(x);
}
vec
}
}
impl<T: 'static> IntoIterator for StaticVec<T> {
type Item = T;
type IntoIter = Box<dyn Iterator<Item = T>>;
fn into_iter(self) -> Self::IntoIter {
self.into_iter()
}
}
impl<T> StaticVec<T> {
/// Create a new `StaticVec`.
pub fn new() -> Self {
Default::default()
}
/// Empty the `StaticVec`.
pub fn clear(&mut self) {
if self.is_fixed_storage() {
for x in 0..self.len {
self.extract_from_list(x);
}
} else {
self.more.clear();
}
self.len = 0;
}
/// Extract a `MaybeUninit` into a concrete initialized type.
fn extract(value: MaybeUninit<T>) -> T {
unsafe { value.assume_init() }
}
/// Extract an item from the fixed-size array, replacing it with `MaybeUninit::uninit()`.
///
/// # Panics
///
/// Panics if fixed-size storage is not used, or if the `index` is out of bounds.
fn extract_from_list(&mut self, index: usize) -> T {
if !self.is_fixed_storage() {
panic!("not fixed storage in StaticVec");
}
if index >= self.len {
panic!("index OOB in StaticVec");
}
Self::extract(mem::replace(
self.list.get_mut(index).unwrap(),
MaybeUninit::uninit(),
))
}
/// Set an item into the fixed-size array.
/// If `drop` is `true`, the original value is extracted then automatically dropped.
///
/// # Panics
///
/// Panics if fixed-size storage is not used, or if the `index` is out of bounds.
fn set_into_list(&mut self, index: usize, value: T, drop: bool) {
if !self.is_fixed_storage() {
panic!("not fixed storage in StaticVec");
}
// Allow setting at most one slot to the right
if index > self.len {
panic!("index OOB in StaticVec");
}
let temp = mem::replace(self.list.get_mut(index).unwrap(), MaybeUninit::new(value));
if drop {
// Extract the original value - which will drop it automatically
Self::extract(temp);
}
}
/// Move item in the fixed-size array into the `Vec`.
///
/// # Panics
///
/// Panics if fixed-size storage is not used, or if the fixed-size storage is not full.
fn move_fixed_into_vec(&mut self, num: usize) {
if !self.is_fixed_storage() {
panic!("not fixed storage in StaticVec");
}
if self.len != num {
panic!("fixed storage is not full in StaticVec");
}
self.more.extend(
self.list
.iter_mut()
.take(num)
.map(|v| mem::replace(v, MaybeUninit::uninit()))
.map(Self::extract),
);
}
/// Is data stored in fixed-size storage?
fn is_fixed_storage(&self) -> bool {
self.len <= MAX_STATIC_VEC
}
/// Push a new value to the end of this `StaticVec`.
pub fn push<X: Into<T>>(&mut self, value: X) {
if self.len == MAX_STATIC_VEC {
self.move_fixed_into_vec(MAX_STATIC_VEC);
self.more.push(value.into());
} else if self.is_fixed_storage() {
self.set_into_list(self.len, value.into(), false);
} else {
self.more.push(value.into());
}
self.len += 1;
}
/// Insert a new value to this `StaticVec` at a particular position.
///
/// # Panics
///
/// Panics if `index` is out of bounds.
pub fn insert<X: Into<T>>(&mut self, index: usize, value: X) {
if index > self.len {
panic!("index OOB in StaticVec");
}
if self.len == MAX_STATIC_VEC {
self.move_fixed_into_vec(MAX_STATIC_VEC);
self.more.insert(index, value.into());
} else if self.is_fixed_storage() {
// Move all items one slot to the right
for x in (index..self.len).rev() {
let orig_value = self.extract_from_list(x);
self.set_into_list(x + 1, orig_value, false);
}
self.set_into_list(index, value.into(), false);
} else {
self.more.insert(index, value.into());
}
self.len += 1;
}
/// Pop a value from the end of this `StaticVec`.
///
/// # Panics
///
/// Panics if the `StaticVec` is empty.
pub fn pop(&mut self) -> T {
if self.is_empty() {
panic!("nothing to pop!");
}
if self.is_fixed_storage() {
let value = self.extract_from_list(self.len - 1);
self.len -= 1;
value
} else {
let value = self.more.pop().unwrap();
self.len -= 1;
// Move back to the fixed list
if self.more.len() == MAX_STATIC_VEC {
for index in (0..MAX_STATIC_VEC).rev() {
let item = self.more.pop().unwrap();
self.set_into_list(index, item, false);
}
}
value
}
}
/// Remove a value from this `StaticVec` at a particular position.
///
/// # Panics
///
/// Panics if `index` is out of bounds.
pub fn remove(&mut self, index: usize) -> T {
if index >= self.len {
panic!("index OOB in StaticVec");
}
if self.is_fixed_storage() {
let value = self.extract_from_list(index);
// Move all items one slot to the left
for x in index + 1..self.len {
let orig_value = self.extract_from_list(x);
self.set_into_list(x - 1, orig_value, false);
}
self.len -= 1;
value
} else {
let value = self.more.remove(index);
self.len -= 1;
// Move back to the fixed list
if self.more.len() == MAX_STATIC_VEC {
for index in (0..MAX_STATIC_VEC).rev() {
let item = self.more.pop().unwrap();
self.set_into_list(index, item, false);
}
}
value
}
}
/// Get the number of items in this `StaticVec`.
pub fn len(&self) -> usize {
self.len
}
/// Is this `StaticVec` empty?
pub fn is_empty(&self) -> bool {
self.len == 0
}
/// Get a reference to the item at a particular index.
///
/// # Panics
///
/// Panics if `index` is out of bounds.
pub fn get(&self, index: usize) -> &T {
if index >= self.len {
panic!("index OOB in StaticVec");
}
let list = unsafe { mem::transmute::<_, &[T; MAX_STATIC_VEC]>(&self.list) };
if self.is_fixed_storage() {
list.get(index).unwrap()
} else {
self.more.get(index).unwrap()
}
}
/// Get a mutable reference to the item at a particular index.
///
/// # Panics
///
/// Panics if `index` is out of bounds.
pub fn get_mut(&mut self, index: usize) -> &mut T {
if index >= self.len {
panic!("index OOB in StaticVec");
}
let list = unsafe { mem::transmute::<_, &mut [T; MAX_STATIC_VEC]>(&mut self.list) };
if self.is_fixed_storage() {
list.get_mut(index).unwrap()
} else {
self.more.get_mut(index).unwrap()
}
}
/// Get an iterator to entries in the `StaticVec`.
pub fn iter(&self) -> impl Iterator<Item = &T> {
let list = unsafe { mem::transmute::<_, &[T; MAX_STATIC_VEC]>(&self.list) };
if self.is_fixed_storage() {
list[..self.len].iter()
} else {
self.more.iter()
}
}
/// Get a mutable iterator to entries in the `StaticVec`.
pub fn iter_mut(&mut self) -> impl Iterator<Item = &mut T> {
let list = unsafe { mem::transmute::<_, &mut [T; MAX_STATIC_VEC]>(&mut self.list) };
if self.is_fixed_storage() {
list[..self.len].iter_mut()
} else {
self.more.iter_mut()
}
}
}
impl<T: 'static> StaticVec<T> {
/// Get a mutable iterator to entries in the `StaticVec`.
pub fn into_iter(mut self) -> Box<dyn Iterator<Item = T>> {
if self.is_fixed_storage() {
let mut it = FixedStorageIterator {
data: unsafe { mem::MaybeUninit::uninit().assume_init() },
index: 0,
limit: self.len,
};
for x in 0..self.len {
it.data[x] = mem::replace(self.list.get_mut(x).unwrap(), MaybeUninit::uninit());
}
self.len = 0;
Box::new(it)
} else {
Box::new(Vec::from(self).into_iter())
}
}
}
/// An iterator that takes control of the fixed-size storage of a `StaticVec` and returns its values.
struct FixedStorageIterator<T> {
data: [MaybeUninit<T>; MAX_STATIC_VEC],
index: usize,
limit: usize,
}
impl<T> Iterator for FixedStorageIterator<T> {
type Item = T;
fn next(&mut self) -> Option<Self::Item> {
if self.index >= self.limit {
None
} else {
self.index += 1;
let value = mem::replace(
self.data.get_mut(self.index - 1).unwrap(),
MaybeUninit::uninit(),
);
unsafe { Some(value.assume_init()) }
}
}
}
impl<T: Default> StaticVec<T> {
/// Get the item at a particular index, replacing it with the default.
///
/// # Panics
///
/// Panics if `index` is out of bounds.
pub fn take(&mut self, index: usize) -> T {
if index >= self.len {
panic!("index OOB in StaticVec");
}
mem::take(if self.is_fixed_storage() {
unsafe { mem::transmute(self.list.get_mut(index).unwrap()) }
} else {
self.more.get_mut(index).unwrap()
})
}
}
impl<T: fmt::Debug> fmt::Debug for StaticVec<T> {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
fmt::Debug::fmt(&self.iter().collect::<Vec<_>>(), f)
}
}
impl<T> AsRef<[T]> for StaticVec<T> {
fn as_ref(&self) -> &[T] {
let list = unsafe { mem::transmute::<_, &[T; MAX_STATIC_VEC]>(&self.list) };
if self.is_fixed_storage() {
&list[..self.len]
} else {
&self.more[..]
}
}
}
impl<T> AsMut<[T]> for StaticVec<T> {
fn as_mut(&mut self) -> &mut [T] {
let list = unsafe { mem::transmute::<_, &mut [T; MAX_STATIC_VEC]>(&mut self.list) };
if self.is_fixed_storage() {
&mut list[..self.len]
} else {
&mut self.more[..]
}
}
}
impl<T> Deref for StaticVec<T> {
type Target = [T];
fn deref(&self) -> &Self::Target {
self.as_ref()
}
}
impl<T> DerefMut for StaticVec<T> {
fn deref_mut(&mut self) -> &mut Self::Target {
self.as_mut()
}
}
impl<T> Index<usize> for StaticVec<T> {
type Output = T;
fn index(&self, index: usize) -> &Self::Output {
self.get(index)
}
}
impl<T> IndexMut<usize> for StaticVec<T> {
fn index_mut(&mut self, index: usize) -> &mut Self::Output {
self.get_mut(index)
}
}
impl<T> From<StaticVec<T>> for Vec<T> {
fn from(mut value: StaticVec<T>) -> Self {
if value.len <= MAX_STATIC_VEC {
value.move_fixed_into_vec(value.len);
}
value.len = 0;
let mut arr = Self::new();
arr.append(&mut value.more);
arr
}
}
impl<T> From<Vec<T>> for StaticVec<T> {
fn from(mut value: Vec<T>) -> Self {
let mut arr: Self = Default::default();
arr.len = value.len();
if arr.len <= MAX_STATIC_VEC {
for x in (0..arr.len).rev() {
arr.set_into_list(x, value.pop().unwrap(), false);
}
} else {
arr.more = value;
}
arr
}
}
pub type StaticVec<T> = SmallVec<[T; 4]>;
/// The system immutable string type.
///