Move EntityList and SparseMap into the entity module.
These data structures are dependent on EntityRef and EntityMap, so it makes sense to keep them in the same module.
This commit is contained in:
Jakob Stoklund Olesen
680
lib/cretonne/src/entity/list.rs
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680
lib/cretonne/src/entity/list.rs
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@@ -0,0 +1,680 @@
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//! Small lists of entity references.
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//!
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//! This module defines an `EntityList<T>` type which provides similar functionality to `Vec<T>`,
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//! but with some important differences in the implementation:
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//!
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//! 1. Memory is allocated from a `ListPool<T>` instead of the global heap.
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//! 2. The footprint of an entity list is 4 bytes, compared with the 24 bytes for `Vec<T>`.
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//! 3. An entity list doesn't implement `Drop`, leaving it to the pool to manage memory.
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//!
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//! The list pool is intended to be used as a LIFO allocator. After building up a larger data
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//! structure with many list references, the whole thing can be discarded quickly by clearing the
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//! pool.
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//!
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//! # Safety
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//!
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//! Entity lists are not as safe to use as `Vec<T>`, but they never jeopardize Rust's memory safety
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//! guarantees. These are the problems to be aware of:
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//!
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//! - If you lose track of an entity list, its memory won't be recycled until the pool is cleared.
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//! This can cause the pool to grow very large with leaked lists.
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//! - If entity lists are used after their pool is cleared, they may contain garbage data, and
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//! modifying them may corrupt other lists in the pool.
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//! - If an entity list is used with two different pool instances, both pools are likely to become
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//! corrupted.
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//!
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//! # Implementation
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//!
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//! The `EntityList` itself is designed to have the smallest possible footprint. This is important
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//! because it is used inside very compact data structures like `InstructionData`. The list
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//! contains only a 32-bit index into the pool's memory vector, pointing to the first element of
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//! the list.
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//!
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//! The pool is just a single `Vec<T>` containing all of the allocated lists. Each list is
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//! represented as three contiguous parts:
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//!
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//! 1. The number of elements in the list.
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//! 2. The list elements.
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//! 3. Excess capacity elements.
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//!
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//! The total size of the three parts is always a power of two, and the excess capacity is always
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//! as small as possible. This means that shrinking a list may cause the excess capacity to shrink
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//! if a smaller power-of-two size becomes available.
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//!
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//! Both growing and shrinking a list may cause it to be reallocated in the pool vector.
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//!
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//! The index stored in an `EntityList` points to part 2, the list elements. The value 0 is
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//! reserved for the empty list which isn't allocated in the vector.
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use entity::EntityRef;
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use std::hash::{Hash, Hasher};
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use std::marker::PhantomData;
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use std::mem;
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/// A small list of entity references allocated from a pool.
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///
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/// All of the list methods that take a pool reference must be given the same pool reference every
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/// time they are called. Otherwise data structures will be corrupted.
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///
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/// Entity lists can be cloned, but that operation should only be used as part of cloning the whole
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/// function they belong to. *Cloning an entity list does not allocate new memory for the clone*.
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/// It creates an alias of the same memory.
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///
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/// Entity lists can also be hashed and compared for equality, but those operations just panic if,
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/// they're ever actually called, because it's not possible to compare the contents of the list
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/// without the pool reference.
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#[derive(Clone, Debug)]
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pub struct EntityList<T: EntityRef> {
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index: u32,
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unused: PhantomData<T>,
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}
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/// Create an empty list.
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impl<T: EntityRef> Default for EntityList<T> {
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fn default() -> Self {
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EntityList {
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index: 0,
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unused: PhantomData,
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}
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}
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}
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impl<T: EntityRef> Hash for EntityList<T> {
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fn hash<H: Hasher>(&self, _: &mut H) {
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panic!("hash called on EntityList");
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}
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}
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impl<T: EntityRef> PartialEq for EntityList<T> {
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fn eq(&self, _: &EntityList<T>) -> bool {
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panic!("eq called on EntityList");
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}
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}
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impl<T: EntityRef> Eq for EntityList<T> {}
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/// A memory pool for storing lists of `T`.
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#[derive(Clone, Debug)]
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pub struct ListPool<T: EntityRef> {
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// The main array containing the lists.
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data: Vec<T>,
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// Heads of the free lists, one for each size class.
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free: Vec<usize>,
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}
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/// Lists are allocated in sizes that are powers of two, starting from 4.
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/// Each power of two is assigned a size class number, so the size is `4 << SizeClass`.
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type SizeClass = u8;
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/// Get the size of a given size class. The size includes the length field, so the maximum list
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/// length is one less than the class size.
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fn sclass_size(sclass: SizeClass) -> usize {
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4 << sclass
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}
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/// Get the size class to use for a given list length.
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/// This always leaves room for the length element in addition to the list elements.
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fn sclass_for_length(len: usize) -> SizeClass {
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30 - (len as u32 | 3).leading_zeros() as SizeClass
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}
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/// Is `len` the minimum length in its size class?
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fn is_sclass_min_length(len: usize) -> bool {
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len > 3 && len.is_power_of_two()
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}
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impl<T: EntityRef> ListPool<T> {
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/// Create a new list pool.
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pub fn new() -> ListPool<T> {
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ListPool {
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data: Vec::new(),
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free: Vec::new(),
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}
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}
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/// Clear the pool, forgetting about all lists that use it.
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///
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/// This invalidates any existing entity lists that used this pool to allocate memory.
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///
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/// The pool's memory is not released to the operating system, but kept around for faster
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/// allocation in the future.
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pub fn clear(&mut self) {
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self.data.clear();
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self.free.clear();
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}
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/// Read the length of a list field, if it exists.
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fn len_of(&self, list: &EntityList<T>) -> Option<usize> {
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let idx = list.index as usize;
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// `idx` points at the list elements. The list length is encoded in the element immediately
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// before the list elements.
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//
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// The `wrapping_sub` handles the special case 0, which is the empty list. This way, the
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// cost of the bounds check that we have to pay anyway is co-opted to handle the special
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// case of the empty list.
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self.data.get(idx.wrapping_sub(1)).map(|len| len.index())
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}
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/// Allocate a storage block with a size given by `sclass`.
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///
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/// Returns the first index of an available segment of `self.data` containing
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/// `sclass_size(sclass)` elements.
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fn alloc(&mut self, sclass: SizeClass) -> usize {
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// First try the free list for this size class.
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match self.free.get(sclass as usize).cloned() {
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Some(head) if head > 0 => {
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// The free list pointers are offset by 1, using 0 to terminate the list.
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// A block on the free list has two entries: `[ 0, next ]`.
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// The 0 is where the length field would be stored for a block in use.
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// The free list heads and the next pointer point at the `next` field.
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self.free[sclass as usize] = self.data[head].index();
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head - 1
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}
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_ => {
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// Nothing on the free list. Allocate more memory.
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let offset = self.data.len();
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// We don't want to mess around with uninitialized data.
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// Just fill it up with nulls.
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self.data.resize(offset + sclass_size(sclass), T::new(0));
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offset
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}
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}
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}
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/// Free a storage block with a size given by `sclass`.
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///
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/// This must be a block that was previously allocated by `alloc()` with the same size class.
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fn free(&mut self, block: usize, sclass: SizeClass) {
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let sclass = sclass as usize;
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// Make sure we have a free-list head for `sclass`.
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if self.free.len() <= sclass {
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self.free.resize(sclass + 1, 0);
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}
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// Make sure the length field is cleared.
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self.data[block] = T::new(0);
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// Insert the block on the free list which is a single linked list.
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self.data[block + 1] = T::new(self.free[sclass]);
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self.free[sclass] = block + 1
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}
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/// Returns two mutable slices representing the two requested blocks.
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///
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/// The two returned slices can be longer than the blocks. Each block is located at the front
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/// of the respective slice.
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fn mut_slices(&mut self, block0: usize, block1: usize) -> (&mut [T], &mut [T]) {
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if block0 < block1 {
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let (s0, s1) = self.data.split_at_mut(block1);
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(&mut s0[block0..], s1)
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} else {
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let (s1, s0) = self.data.split_at_mut(block0);
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(s0, &mut s1[block1..])
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}
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}
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/// Reallocate a block to a different size class.
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///
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/// Copy `elems_to_copy` elements from the old to the new block.
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fn realloc(&mut self,
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block: usize,
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from_sclass: SizeClass,
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to_sclass: SizeClass,
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elems_to_copy: usize)
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-> usize {
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assert!(elems_to_copy <= sclass_size(from_sclass));
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assert!(elems_to_copy <= sclass_size(to_sclass));
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let new_block = self.alloc(to_sclass);
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if elems_to_copy > 0 {
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let (old, new) = self.mut_slices(block, new_block);
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(&mut new[0..elems_to_copy]).copy_from_slice(&old[0..elems_to_copy]);
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}
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self.free(block, from_sclass);
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new_block
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}
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}
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impl<T: EntityRef> EntityList<T> {
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/// Create a new empty list.
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pub fn new() -> Self {
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Default::default()
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}
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/// Returns `true` if the list has a length of 0.
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pub fn is_empty(&self) -> bool {
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// 0 is a magic value for the empty list. Any list in the pool array must have a positive
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// length.
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self.index == 0
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}
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/// Get the number of elements in the list.
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pub fn len(&self, pool: &ListPool<T>) -> usize {
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// Both the empty list and any invalidated old lists will return `None`.
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pool.len_of(self).unwrap_or(0)
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}
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/// Returns `true` if the list is valid
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pub fn is_valid(&self, pool: &ListPool<T>) -> bool {
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// We consider an empty list to be valid
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self.is_empty() || pool.len_of(self) != None
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}
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/// Get the list as a slice.
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pub fn as_slice<'a>(&'a self, pool: &'a ListPool<T>) -> &'a [T] {
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let idx = self.index as usize;
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match pool.len_of(self) {
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None => &[],
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Some(len) => &pool.data[idx..idx + len],
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}
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}
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/// Get a single element from the list.
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pub fn get(&self, index: usize, pool: &ListPool<T>) -> Option<T> {
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self.as_slice(pool).get(index).cloned()
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}
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/// Get the first element from the list.
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pub fn first(&self, pool: &ListPool<T>) -> Option<T> {
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if self.is_empty() {
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None
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} else {
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Some(pool.data[self.index as usize])
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}
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}
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/// Get the list as a mutable slice.
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pub fn as_mut_slice<'a>(&'a mut self, pool: &'a mut ListPool<T>) -> &'a mut [T] {
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let idx = self.index as usize;
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match pool.len_of(self) {
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None => &mut [],
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Some(len) => &mut pool.data[idx..idx + len],
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}
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}
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/// Get a mutable reference to a single element from the list.
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pub fn get_mut<'a>(&'a mut self, index: usize, pool: &'a mut ListPool<T>) -> Option<&'a mut T> {
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self.as_mut_slice(pool).get_mut(index)
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}
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/// Removes all elements from the list.
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///
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/// The memory used by the list is put back in the pool.
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pub fn clear(&mut self, pool: &mut ListPool<T>) {
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let idx = self.index as usize;
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match pool.len_of(self) {
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None => assert_eq!(idx, 0, "Invalid pool"),
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Some(len) => pool.free(idx - 1, sclass_for_length(len)),
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}
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// Switch back to the empty list representation which has no storage.
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self.index = 0;
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}
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/// Take all elements from this list and return them as a new list. Leave this list empty.
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///
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/// This is the equivalent of `Option::take()`.
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pub fn take(&mut self) -> EntityList<T> {
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mem::replace(self, Default::default())
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}
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/// Appends an element to the back of the list.
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/// Returns the index where the element was inserted.
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pub fn push(&mut self, element: T, pool: &mut ListPool<T>) -> usize {
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let idx = self.index as usize;
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match pool.len_of(self) {
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None => {
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// This is an empty list. Allocate a block and set length=1.
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assert_eq!(idx, 0, "Invalid pool");
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let block = pool.alloc(sclass_for_length(1));
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pool.data[block] = T::new(1);
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pool.data[block + 1] = element;
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self.index = (block + 1) as u32;
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0
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}
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Some(len) => {
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// Do we need to reallocate?
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let new_len = len + 1;
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let block;
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if is_sclass_min_length(new_len) {
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// Reallocate, preserving length + all old elements.
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let sclass = sclass_for_length(len);
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block = pool.realloc(idx - 1, sclass, sclass + 1, len + 1);
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self.index = (block + 1) as u32;
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} else {
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block = idx - 1;
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}
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pool.data[block + new_len] = element;
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pool.data[block] = T::new(new_len);
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len
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}
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}
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}
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/// Grow list by adding `count` uninitialized elements at the end.
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///
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/// Returns a mutable slice representing the whole list.
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fn grow<'a>(&'a mut self, count: usize, pool: &'a mut ListPool<T>) -> &'a mut [T] {
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let idx = self.index as usize;
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let new_len;
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let block;
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match pool.len_of(self) {
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None => {
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// This is an empty list. Allocate a block.
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assert_eq!(idx, 0, "Invalid pool");
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if count == 0 {
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return &mut [];
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}
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new_len = count;
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block = pool.alloc(sclass_for_length(new_len));
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self.index = (block + 1) as u32;
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}
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Some(len) => {
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// Do we need to reallocate?
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let sclass = sclass_for_length(len);
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new_len = len + count;
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let new_sclass = sclass_for_length(new_len);
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if new_sclass != sclass {
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block = pool.realloc(idx - 1, sclass, new_sclass, len + 1);
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self.index = (block + 1) as u32;
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} else {
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block = idx - 1;
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}
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}
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}
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pool.data[block] = T::new(new_len);
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&mut pool.data[block + 1..block + 1 + new_len]
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}
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/// Appends multiple elements to the back of the list.
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pub fn extend<I>(&mut self, elements: I, pool: &mut ListPool<T>)
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where I: IntoIterator<Item = T>
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{
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// TODO: use `size_hint()` to reduce reallocations.
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for x in elements {
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self.push(x, pool);
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}
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}
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/// Inserts an element as position `index` in the list, shifting all elements after it to the
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/// right.
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pub fn insert(&mut self, index: usize, element: T, pool: &mut ListPool<T>) {
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// Increase size by 1.
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self.push(element, pool);
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// Move tail elements.
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let seq = self.as_mut_slice(pool);
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if index < seq.len() {
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let tail = &mut seq[index..];
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for i in (1..tail.len()).rev() {
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tail[i] = tail[i - 1];
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||||
}
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tail[0] = element;
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||||
} else {
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||||
assert_eq!(index, seq.len());
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||||
}
|
||||
}
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/// Removes the element at position `index` from the list. Potentially linear complexity.
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pub fn remove(&mut self, index: usize, pool: &mut ListPool<T>) {
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let len;
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||||
{
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let seq = self.as_mut_slice(pool);
|
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len = seq.len();
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||||
assert!(index < len);
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||||
|
||||
// Copy elements down.
|
||||
for i in index..len - 1 {
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seq[i] = seq[i + 1];
|
||||
}
|
||||
}
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||||
|
||||
// Check if we deleted the last element.
|
||||
if len == 1 {
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||||
self.clear(pool);
|
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return;
|
||||
}
|
||||
|
||||
// Do we need to reallocate to a smaller size class?
|
||||
let mut block = self.index as usize - 1;
|
||||
if is_sclass_min_length(len) {
|
||||
let sclass = sclass_for_length(len);
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||||
block = pool.realloc(block, sclass, sclass - 1, len);
|
||||
self.index = (block + 1) as u32;
|
||||
}
|
||||
|
||||
// Finally adjust the length.
|
||||
pool.data[block] = T::new(len - 1);
|
||||
}
|
||||
|
||||
/// Removes the element at `index` in constant time by switching it with the last element of
|
||||
/// the list.
|
||||
pub fn swap_remove(&mut self, index: usize, pool: &mut ListPool<T>) {
|
||||
let len = self.len(pool);
|
||||
assert!(index < len);
|
||||
if index == len - 1 {
|
||||
self.remove(index, pool);
|
||||
} else {
|
||||
{
|
||||
let seq = self.as_mut_slice(pool);
|
||||
seq.swap(index, len - 1);
|
||||
}
|
||||
self.remove(len - 1, pool);
|
||||
}
|
||||
}
|
||||
|
||||
/// Grow the list by inserting `count` elements at `index`.
|
||||
///
|
||||
/// The new elements are not initialized, they will contain whatever happened to be in memory.
|
||||
/// Since the memory comes from the pool, this will be either zero entity references or
|
||||
/// whatever where in a previously deallocated list.
|
||||
pub fn grow_at(&mut self, index: usize, count: usize, pool: &mut ListPool<T>) {
|
||||
let mut data = self.grow(count, pool);
|
||||
|
||||
// Copy elements after `index` up.
|
||||
for i in (index + count..data.len()).rev() {
|
||||
data[i] = data[i - count];
|
||||
}
|
||||
}
|
||||
}
|
||||
|
||||
#[cfg(test)]
|
||||
mod tests {
|
||||
use super::*;
|
||||
use super::{sclass_size, sclass_for_length};
|
||||
use ir::Inst;
|
||||
use entity::EntityRef;
|
||||
|
||||
#[test]
|
||||
fn size_classes() {
|
||||
assert_eq!(sclass_size(0), 4);
|
||||
assert_eq!(sclass_for_length(0), 0);
|
||||
assert_eq!(sclass_for_length(1), 0);
|
||||
assert_eq!(sclass_for_length(2), 0);
|
||||
assert_eq!(sclass_for_length(3), 0);
|
||||
assert_eq!(sclass_for_length(4), 1);
|
||||
assert_eq!(sclass_for_length(7), 1);
|
||||
assert_eq!(sclass_for_length(8), 2);
|
||||
assert_eq!(sclass_size(1), 8);
|
||||
for l in 0..300 {
|
||||
assert!(sclass_size(sclass_for_length(l)) >= l + 1);
|
||||
}
|
||||
}
|
||||
|
||||
#[test]
|
||||
fn block_allocator() {
|
||||
let mut pool = ListPool::<Inst>::new();
|
||||
let b1 = pool.alloc(0);
|
||||
let b2 = pool.alloc(1);
|
||||
let b3 = pool.alloc(0);
|
||||
assert_ne!(b1, b2);
|
||||
assert_ne!(b1, b3);
|
||||
assert_ne!(b2, b3);
|
||||
pool.free(b2, 1);
|
||||
let b2a = pool.alloc(1);
|
||||
let b2b = pool.alloc(1);
|
||||
assert_ne!(b2a, b2b);
|
||||
// One of these should reuse the freed block.
|
||||
assert!(b2a == b2 || b2b == b2);
|
||||
|
||||
// Check the free lists for a size class smaller than the largest seen so far.
|
||||
pool.free(b1, 0);
|
||||
pool.free(b3, 0);
|
||||
let b1a = pool.alloc(0);
|
||||
let b3a = pool.alloc(0);
|
||||
assert_ne!(b1a, b3a);
|
||||
assert!(b1a == b1 || b1a == b3);
|
||||
assert!(b3a == b1 || b3a == b3);
|
||||
}
|
||||
|
||||
#[test]
|
||||
fn empty_list() {
|
||||
let pool = &mut ListPool::<Inst>::new();
|
||||
let mut list = EntityList::<Inst>::default();
|
||||
{
|
||||
let ilist = &list;
|
||||
assert!(ilist.is_empty());
|
||||
assert_eq!(ilist.len(pool), 0);
|
||||
assert_eq!(ilist.as_slice(pool), &[]);
|
||||
assert_eq!(ilist.get(0, pool), None);
|
||||
assert_eq!(ilist.get(100, pool), None);
|
||||
}
|
||||
assert_eq!(list.as_mut_slice(pool), &[]);
|
||||
assert_eq!(list.get_mut(0, pool), None);
|
||||
assert_eq!(list.get_mut(100, pool), None);
|
||||
|
||||
list.clear(pool);
|
||||
assert!(list.is_empty());
|
||||
assert_eq!(list.len(pool), 0);
|
||||
assert_eq!(list.as_slice(pool), &[]);
|
||||
assert_eq!(list.first(pool), None);
|
||||
}
|
||||
|
||||
#[test]
|
||||
fn push() {
|
||||
let pool = &mut ListPool::<Inst>::new();
|
||||
let mut list = EntityList::<Inst>::default();
|
||||
|
||||
let i1 = Inst::new(1);
|
||||
let i2 = Inst::new(2);
|
||||
let i3 = Inst::new(3);
|
||||
let i4 = Inst::new(4);
|
||||
|
||||
assert_eq!(list.push(i1, pool), 0);
|
||||
assert_eq!(list.len(pool), 1);
|
||||
assert!(!list.is_empty());
|
||||
assert_eq!(list.as_slice(pool), &[i1]);
|
||||
assert_eq!(list.first(pool), Some(i1));
|
||||
assert_eq!(list.get(0, pool), Some(i1));
|
||||
assert_eq!(list.get(1, pool), None);
|
||||
|
||||
assert_eq!(list.push(i2, pool), 1);
|
||||
assert_eq!(list.len(pool), 2);
|
||||
assert!(!list.is_empty());
|
||||
assert_eq!(list.as_slice(pool), &[i1, i2]);
|
||||
assert_eq!(list.first(pool), Some(i1));
|
||||
assert_eq!(list.get(0, pool), Some(i1));
|
||||
assert_eq!(list.get(1, pool), Some(i2));
|
||||
assert_eq!(list.get(2, pool), None);
|
||||
|
||||
assert_eq!(list.push(i3, pool), 2);
|
||||
assert_eq!(list.len(pool), 3);
|
||||
assert!(!list.is_empty());
|
||||
assert_eq!(list.as_slice(pool), &[i1, i2, i3]);
|
||||
assert_eq!(list.first(pool), Some(i1));
|
||||
assert_eq!(list.get(0, pool), Some(i1));
|
||||
assert_eq!(list.get(1, pool), Some(i2));
|
||||
assert_eq!(list.get(2, pool), Some(i3));
|
||||
assert_eq!(list.get(3, pool), None);
|
||||
|
||||
// This triggers a reallocation.
|
||||
assert_eq!(list.push(i4, pool), 3);
|
||||
assert_eq!(list.len(pool), 4);
|
||||
assert!(!list.is_empty());
|
||||
assert_eq!(list.as_slice(pool), &[i1, i2, i3, i4]);
|
||||
assert_eq!(list.first(pool), Some(i1));
|
||||
assert_eq!(list.get(0, pool), Some(i1));
|
||||
assert_eq!(list.get(1, pool), Some(i2));
|
||||
assert_eq!(list.get(2, pool), Some(i3));
|
||||
assert_eq!(list.get(3, pool), Some(i4));
|
||||
assert_eq!(list.get(4, pool), None);
|
||||
|
||||
list.extend([i1, i1, i2, i2, i3, i3, i4, i4].iter().cloned(), pool);
|
||||
assert_eq!(list.len(pool), 12);
|
||||
assert_eq!(list.as_slice(pool),
|
||||
&[i1, i2, i3, i4, i1, i1, i2, i2, i3, i3, i4, i4]);
|
||||
}
|
||||
|
||||
#[test]
|
||||
fn insert_remove() {
|
||||
let pool = &mut ListPool::<Inst>::new();
|
||||
let mut list = EntityList::<Inst>::default();
|
||||
|
||||
let i1 = Inst::new(1);
|
||||
let i2 = Inst::new(2);
|
||||
let i3 = Inst::new(3);
|
||||
let i4 = Inst::new(4);
|
||||
|
||||
list.insert(0, i4, pool);
|
||||
assert_eq!(list.as_slice(pool), &[i4]);
|
||||
|
||||
list.insert(0, i3, pool);
|
||||
assert_eq!(list.as_slice(pool), &[i3, i4]);
|
||||
|
||||
list.insert(2, i2, pool);
|
||||
assert_eq!(list.as_slice(pool), &[i3, i4, i2]);
|
||||
|
||||
list.insert(2, i1, pool);
|
||||
assert_eq!(list.as_slice(pool), &[i3, i4, i1, i2]);
|
||||
|
||||
list.remove(3, pool);
|
||||
assert_eq!(list.as_slice(pool), &[i3, i4, i1]);
|
||||
|
||||
list.remove(2, pool);
|
||||
assert_eq!(list.as_slice(pool), &[i3, i4]);
|
||||
|
||||
list.remove(0, pool);
|
||||
assert_eq!(list.as_slice(pool), &[i4]);
|
||||
|
||||
list.remove(0, pool);
|
||||
assert_eq!(list.as_slice(pool), &[]);
|
||||
assert!(list.is_empty());
|
||||
}
|
||||
|
||||
#[test]
|
||||
fn growing() {
|
||||
let pool = &mut ListPool::<Inst>::new();
|
||||
let mut list = EntityList::<Inst>::default();
|
||||
|
||||
let i1 = Inst::new(1);
|
||||
let i2 = Inst::new(2);
|
||||
let i3 = Inst::new(3);
|
||||
let i4 = Inst::new(4);
|
||||
|
||||
// This is not supposed to change the list.
|
||||
list.grow_at(0, 0, pool);
|
||||
assert_eq!(list.len(pool), 0);
|
||||
assert!(list.is_empty());
|
||||
|
||||
list.grow_at(0, 2, pool);
|
||||
assert_eq!(list.len(pool), 2);
|
||||
|
||||
list.as_mut_slice(pool).copy_from_slice(&[i2, i3]);
|
||||
|
||||
list.grow_at(1, 0, pool);
|
||||
assert_eq!(list.as_slice(pool), &[i2, i3]);
|
||||
|
||||
list.grow_at(1, 1, pool);
|
||||
list.as_mut_slice(pool)[1] = i1;
|
||||
assert_eq!(list.as_slice(pool), &[i2, i1, i3]);
|
||||
|
||||
// Append nothing at the end.
|
||||
list.grow_at(3, 0, pool);
|
||||
assert_eq!(list.as_slice(pool), &[i2, i1, i3]);
|
||||
|
||||
// Append something at the end.
|
||||
list.grow_at(3, 1, pool);
|
||||
list.as_mut_slice(pool)[3] = i4;
|
||||
assert_eq!(list.as_slice(pool), &[i2, i1, i3, i4]);
|
||||
}
|
||||
}
|
||||
@@ -6,12 +6,16 @@
|
||||
//! Various data structures based on the entity references are defined in sub-modules.
|
||||
|
||||
mod keys;
|
||||
mod list;
|
||||
mod map;
|
||||
mod primary;
|
||||
mod sparse;
|
||||
|
||||
pub use self::keys::Keys;
|
||||
pub use self::list::{EntityList, ListPool};
|
||||
pub use self::map::EntityMap;
|
||||
pub use self::primary::PrimaryMap;
|
||||
pub use self::sparse::{SparseSet, SparseMap, SparseMapValue};
|
||||
|
||||
/// A type wrapping a small integer index should implement `EntityRef` so it can be used as the key
|
||||
/// of an `EntityMap` or `SparseMap`.
|
||||
|
||||
347
lib/cretonne/src/entity/sparse.rs
Normal file
347
lib/cretonne/src/entity/sparse.rs
Normal file
@@ -0,0 +1,347 @@
|
||||
//! Sparse mapping of entity references to larger value types.
|
||||
//!
|
||||
//! This module provides a `SparseMap` data structure which implements a sparse mapping from an
|
||||
//! `EntityRef` key to a value type that may be on the larger side. This implementation is based on
|
||||
//! the paper:
|
||||
//!
|
||||
//! > Briggs, Torczon, *An efficient representation for sparse sets*,
|
||||
//! ACM Letters on Programming Languages and Systems, Volume 2, Issue 1-4, March-Dec. 1993.
|
||||
//!
|
||||
//! A `SparseMap<K, V>` map provides:
|
||||
//!
|
||||
//! - Memory usage equivalent to `EntityMap<K, u32>` + `Vec<V>`, so much smaller than
|
||||
//! `EntityMap<K, V>` for sparse mappings of larger `V` types.
|
||||
//! - Constant time lookup, slightly slower than `EntityMap`.
|
||||
//! - A very fast, constant time `clear()` operation.
|
||||
//! - Fast insert and erase operations.
|
||||
//! - Stable iteration that is as fast as a `Vec<V>`.
|
||||
//!
|
||||
//! # Compared to `EntityMap`
|
||||
//!
|
||||
//! When should we use a `SparseMap` instead of a secondary `EntityMap`? First of all, `SparseMap`
|
||||
//! does not provide the functionality of a primary `EntityMap` which can allocate and assign
|
||||
//! entity references to objects as they are pushed onto the map. It is only the secondary
|
||||
//! entity maps that can be replaced with a `SparseMap`.
|
||||
//!
|
||||
//! - A secondary entity map requires its values to implement `Default`, and it is a bit loose
|
||||
//! about creating new mappings to the default value. It doesn't distinguish clearly between an
|
||||
//! unmapped key and one that maps to the default value. `SparseMap` does not require `Default`
|
||||
//! values, and it tracks accurately if a key has been mapped or not.
|
||||
//! - Iterating over the contents of an `EntityMap` is linear in the size of the *key space*, while
|
||||
//! iterating over a `SparseMap` is linear in the number of elements in the mapping. This is an
|
||||
//! advantage precisely when the mapping is sparse.
|
||||
//! - `SparseMap::clear()` is constant time and super-fast. `EntityMap::clear()` is linear in the
|
||||
//! size of the key space. (Or, rather the required `resize()` call following the `clear()` is).
|
||||
//! - `SparseMap` requires the values to implement `SparseMapValue<K>` which means that they must
|
||||
//! contain their own key.
|
||||
|
||||
use entity::{EntityRef, EntityMap};
|
||||
use std::mem;
|
||||
use std::slice;
|
||||
use std::u32;
|
||||
|
||||
/// Trait for extracting keys from values stored in a `SparseMap`.
|
||||
///
|
||||
/// All values stored in a `SparseMap` must keep track of their own key in the map and implement
|
||||
/// this trait to provide access to the key.
|
||||
pub trait SparseMapValue<K> {
|
||||
/// Get the key of this sparse map value. This key is not allowed to change while the value
|
||||
/// is a member of the map.
|
||||
fn key(&self) -> K;
|
||||
}
|
||||
|
||||
/// A sparse mapping of entity references.
|
||||
pub struct SparseMap<K, V>
|
||||
where K: EntityRef,
|
||||
V: SparseMapValue<K>
|
||||
{
|
||||
sparse: EntityMap<K, u32>,
|
||||
dense: Vec<V>,
|
||||
}
|
||||
|
||||
impl<K, V> SparseMap<K, V>
|
||||
where K: EntityRef,
|
||||
V: SparseMapValue<K>
|
||||
{
|
||||
/// Create a new empty mapping.
|
||||
pub fn new() -> Self {
|
||||
SparseMap {
|
||||
sparse: EntityMap::new(),
|
||||
dense: Vec::new(),
|
||||
}
|
||||
}
|
||||
|
||||
/// Returns the number of elements in the map.
|
||||
pub fn len(&self) -> usize {
|
||||
self.dense.len()
|
||||
}
|
||||
|
||||
/// Returns true is the map contains no elements.
|
||||
pub fn is_empty(&self) -> bool {
|
||||
self.dense.is_empty()
|
||||
}
|
||||
|
||||
/// Remove all elements from the mapping.
|
||||
pub fn clear(&mut self) {
|
||||
self.dense.clear();
|
||||
}
|
||||
|
||||
/// Returns a reference to the value corresponding to the key.
|
||||
pub fn get(&self, key: K) -> Option<&V> {
|
||||
if let Some(idx) = self.sparse.get(key).cloned() {
|
||||
if let Some(entry) = self.dense.get(idx as usize) {
|
||||
if entry.key() == key {
|
||||
return Some(entry);
|
||||
}
|
||||
}
|
||||
}
|
||||
None
|
||||
}
|
||||
|
||||
/// Returns a mutable reference to the value corresponding to the key.
|
||||
///
|
||||
/// Note that the returned value must not be mutated in a way that would change its key. This
|
||||
/// would invalidate the sparse set data structure.
|
||||
pub fn get_mut(&mut self, key: K) -> Option<&mut V> {
|
||||
if let Some(idx) = self.sparse.get(key).cloned() {
|
||||
if let Some(entry) = self.dense.get_mut(idx as usize) {
|
||||
if entry.key() == key {
|
||||
return Some(entry);
|
||||
}
|
||||
}
|
||||
}
|
||||
None
|
||||
}
|
||||
|
||||
/// Return the index into `dense` of the value corresponding to `key`.
|
||||
fn index(&self, key: K) -> Option<usize> {
|
||||
if let Some(idx) = self.sparse.get(key).cloned() {
|
||||
let idx = idx as usize;
|
||||
if let Some(entry) = self.dense.get(idx) {
|
||||
if entry.key() == key {
|
||||
return Some(idx);
|
||||
}
|
||||
}
|
||||
}
|
||||
None
|
||||
}
|
||||
|
||||
/// Return `true` if the map contains a value corresponding to `key`.
|
||||
pub fn contains_key(&self, key: K) -> bool {
|
||||
self.get(key).is_some()
|
||||
}
|
||||
|
||||
/// Insert a value into the map.
|
||||
///
|
||||
/// If the map did not have this key present, `None` is returned.
|
||||
///
|
||||
/// If the map did have this key present, the value is updated, and the old value is returned.
|
||||
///
|
||||
/// It is not necessary to provide a key since the value knows its own key already.
|
||||
pub fn insert(&mut self, value: V) -> Option<V> {
|
||||
let key = value.key();
|
||||
|
||||
// Replace the existing entry for `key` if there is one.
|
||||
if let Some(entry) = self.get_mut(key) {
|
||||
return Some(mem::replace(entry, value));
|
||||
}
|
||||
|
||||
// There was no previous entry for `key`. Add it to the end of `dense`.
|
||||
let idx = self.dense.len();
|
||||
assert!(idx <= u32::MAX as usize, "SparseMap overflow");
|
||||
self.dense.push(value);
|
||||
self.sparse[key] = idx as u32;
|
||||
None
|
||||
}
|
||||
|
||||
/// Remove a value from the map and return it.
|
||||
pub fn remove(&mut self, key: K) -> Option<V> {
|
||||
if let Some(idx) = self.index(key) {
|
||||
let back = self.dense.pop().unwrap();
|
||||
|
||||
// Are we popping the back of `dense`?
|
||||
if idx == self.dense.len() {
|
||||
return Some(back);
|
||||
}
|
||||
|
||||
// We're removing an element from the middle of `dense`.
|
||||
// Replace the element at `idx` with the back of `dense`.
|
||||
// Repair `sparse` first.
|
||||
self.sparse[back.key()] = idx as u32;
|
||||
return Some(mem::replace(&mut self.dense[idx], back));
|
||||
}
|
||||
|
||||
// Nothing to remove.
|
||||
None
|
||||
}
|
||||
|
||||
/// Get an iterator over the values in the map.
|
||||
///
|
||||
/// The iteration order is entirely determined by the preceding sequence of `insert` and
|
||||
/// `remove` operations. In particular, if no elements were removed, this is the insertion
|
||||
/// order.
|
||||
pub fn values(&self) -> slice::Iter<V> {
|
||||
self.dense.iter()
|
||||
}
|
||||
|
||||
/// Get the values as a slice.
|
||||
pub fn as_slice(&self) -> &[V] {
|
||||
self.dense.as_slice()
|
||||
}
|
||||
}
|
||||
|
||||
/// Iterating over the elements of a set.
|
||||
impl<'a, K, V> IntoIterator for &'a SparseMap<K, V>
|
||||
where K: EntityRef,
|
||||
V: SparseMapValue<K>
|
||||
{
|
||||
type Item = &'a V;
|
||||
type IntoIter = slice::Iter<'a, V>;
|
||||
|
||||
fn into_iter(self) -> Self::IntoIter {
|
||||
self.values()
|
||||
}
|
||||
}
|
||||
|
||||
/// Any `EntityRef` can be used as a sparse map value representing itself.
|
||||
impl<T> SparseMapValue<T> for T
|
||||
where T: EntityRef
|
||||
{
|
||||
fn key(&self) -> T {
|
||||
*self
|
||||
}
|
||||
}
|
||||
|
||||
/// A sparse set of entity references.
|
||||
///
|
||||
/// Any type that implements `EntityRef` can be used as a sparse set value too.
|
||||
pub type SparseSet<T> = SparseMap<T, T>;
|
||||
|
||||
#[cfg(test)]
|
||||
mod tests {
|
||||
use super::*;
|
||||
use entity::EntityRef;
|
||||
use ir::Inst;
|
||||
|
||||
// Mock key-value object for testing.
|
||||
#[derive(PartialEq, Eq, Debug)]
|
||||
struct Obj(Inst, &'static str);
|
||||
|
||||
impl SparseMapValue<Inst> for Obj {
|
||||
fn key(&self) -> Inst {
|
||||
self.0
|
||||
}
|
||||
}
|
||||
|
||||
#[test]
|
||||
fn empty_immutable_map() {
|
||||
let i1 = Inst::new(1);
|
||||
let map: SparseMap<Inst, Obj> = SparseMap::new();
|
||||
|
||||
assert!(map.is_empty());
|
||||
assert_eq!(map.len(), 0);
|
||||
assert_eq!(map.get(i1), None);
|
||||
assert_eq!(map.values().count(), 0);
|
||||
}
|
||||
|
||||
#[test]
|
||||
fn single_entry() {
|
||||
let i0 = Inst::new(0);
|
||||
let i1 = Inst::new(1);
|
||||
let i2 = Inst::new(2);
|
||||
let mut map = SparseMap::new();
|
||||
|
||||
assert!(map.is_empty());
|
||||
assert_eq!(map.len(), 0);
|
||||
assert_eq!(map.get(i1), None);
|
||||
assert_eq!(map.get_mut(i1), None);
|
||||
assert_eq!(map.remove(i1), None);
|
||||
|
||||
assert_eq!(map.insert(Obj(i1, "hi")), None);
|
||||
assert!(!map.is_empty());
|
||||
assert_eq!(map.len(), 1);
|
||||
assert_eq!(map.get(i0), None);
|
||||
assert_eq!(map.get(i1), Some(&Obj(i1, "hi")));
|
||||
assert_eq!(map.get(i2), None);
|
||||
assert_eq!(map.get_mut(i0), None);
|
||||
assert_eq!(map.get_mut(i1), Some(&mut Obj(i1, "hi")));
|
||||
assert_eq!(map.get_mut(i2), None);
|
||||
|
||||
assert_eq!(map.remove(i0), None);
|
||||
assert_eq!(map.remove(i2), None);
|
||||
assert_eq!(map.remove(i1), Some(Obj(i1, "hi")));
|
||||
assert_eq!(map.len(), 0);
|
||||
assert_eq!(map.get(i1), None);
|
||||
assert_eq!(map.get_mut(i1), None);
|
||||
assert_eq!(map.remove(i0), None);
|
||||
assert_eq!(map.remove(i1), None);
|
||||
assert_eq!(map.remove(i2), None);
|
||||
}
|
||||
|
||||
#[test]
|
||||
fn multiple_entries() {
|
||||
let i0 = Inst::new(0);
|
||||
let i1 = Inst::new(1);
|
||||
let i2 = Inst::new(2);
|
||||
let i3 = Inst::new(3);
|
||||
let mut map = SparseMap::new();
|
||||
|
||||
assert_eq!(map.insert(Obj(i2, "foo")), None);
|
||||
assert_eq!(map.insert(Obj(i1, "bar")), None);
|
||||
assert_eq!(map.insert(Obj(i0, "baz")), None);
|
||||
|
||||
// Iteration order = insertion order when nothing has been removed yet.
|
||||
assert_eq!(map.values().map(|obj| obj.1).collect::<Vec<_>>(),
|
||||
["foo", "bar", "baz"]);
|
||||
|
||||
assert_eq!(map.len(), 3);
|
||||
assert_eq!(map.get(i0), Some(&Obj(i0, "baz")));
|
||||
assert_eq!(map.get(i1), Some(&Obj(i1, "bar")));
|
||||
assert_eq!(map.get(i2), Some(&Obj(i2, "foo")));
|
||||
assert_eq!(map.get(i3), None);
|
||||
|
||||
// Remove front object, causing back to be swapped down.
|
||||
assert_eq!(map.remove(i1), Some(Obj(i1, "bar")));
|
||||
assert_eq!(map.len(), 2);
|
||||
assert_eq!(map.get(i0), Some(&Obj(i0, "baz")));
|
||||
assert_eq!(map.get(i1), None);
|
||||
assert_eq!(map.get(i2), Some(&Obj(i2, "foo")));
|
||||
assert_eq!(map.get(i3), None);
|
||||
|
||||
// Reinsert something at a previously used key.
|
||||
assert_eq!(map.insert(Obj(i1, "barbar")), None);
|
||||
assert_eq!(map.len(), 3);
|
||||
assert_eq!(map.get(i0), Some(&Obj(i0, "baz")));
|
||||
assert_eq!(map.get(i1), Some(&Obj(i1, "barbar")));
|
||||
assert_eq!(map.get(i2), Some(&Obj(i2, "foo")));
|
||||
assert_eq!(map.get(i3), None);
|
||||
|
||||
// Replace an entry.
|
||||
assert_eq!(map.insert(Obj(i0, "bazbaz")), Some(Obj(i0, "baz")));
|
||||
assert_eq!(map.len(), 3);
|
||||
assert_eq!(map.get(i0), Some(&Obj(i0, "bazbaz")));
|
||||
assert_eq!(map.get(i1), Some(&Obj(i1, "barbar")));
|
||||
assert_eq!(map.get(i2), Some(&Obj(i2, "foo")));
|
||||
assert_eq!(map.get(i3), None);
|
||||
|
||||
// Check the reference `IntoIter` impl.
|
||||
let mut v = Vec::new();
|
||||
for i in &map {
|
||||
v.push(i.1);
|
||||
}
|
||||
assert_eq!(v.len(), map.len());
|
||||
}
|
||||
|
||||
#[test]
|
||||
fn entity_set() {
|
||||
let i0 = Inst::new(0);
|
||||
let i1 = Inst::new(1);
|
||||
let mut set = SparseSet::new();
|
||||
|
||||
assert_eq!(set.insert(i0), None);
|
||||
assert_eq!(set.insert(i0), Some(i0));
|
||||
assert_eq!(set.insert(i1), None);
|
||||
assert_eq!(set.get(i0), Some(&i0));
|
||||
assert_eq!(set.get(i1), Some(&i1));
|
||||
}
|
||||
}
|
||||
Reference in New Issue
Block a user