polars_utils/
arena.rs

1#[cfg(feature = "ir_serde")]
2use serde::{Deserialize, Serialize};
3
4use crate::error::*;
5use crate::relaxed_cell::RelaxedCell;
6
7unsafe fn index_of_unchecked<T>(slice: &[T], item: &T) -> usize {
8    (item as *const _ as usize - slice.as_ptr() as usize) / size_of::<T>()
9}
10
11fn index_of<T>(slice: &[T], item: &T) -> Option<usize> {
12    debug_assert!(size_of::<T>() > 0);
13    let ptr = item as *const T;
14    unsafe {
15        if slice.as_ptr() < ptr && slice.as_ptr().add(slice.len()) > ptr {
16            Some(index_of_unchecked(slice, item))
17        } else {
18            None
19        }
20    }
21}
22
23#[derive(Clone, Copy, Debug, PartialEq, Eq, Hash, Ord, PartialOrd)]
24#[repr(transparent)]
25#[cfg_attr(feature = "ir_serde", derive(Serialize, Deserialize))]
26pub struct Node(pub usize);
27
28impl Default for Node {
29    fn default() -> Self {
30        Node(usize::MAX)
31    }
32}
33
34static ARENA_VERSION: RelaxedCell<u32> = RelaxedCell::new_u32(0);
35
36#[derive(Debug, Clone)]
37#[cfg_attr(feature = "ir_serde", derive(Serialize, Deserialize))]
38pub struct Arena<T> {
39    version: u32,
40    items: Vec<T>,
41}
42
43impl<T> Default for Arena<T> {
44    fn default() -> Self {
45        Self::new()
46    }
47}
48
49/// Simple Arena implementation
50/// Allocates memory and stores item in a Vec. Only deallocates when being dropped itself.
51impl<T> Arena<T> {
52    #[inline]
53    pub fn version(&self) -> u32 {
54        self.version
55    }
56
57    pub fn add(&mut self, val: T) -> Node {
58        let idx = self.items.len();
59        self.items.push(val);
60        Node(idx)
61    }
62
63    pub fn pop(&mut self) -> Option<T> {
64        self.items.pop()
65    }
66
67    pub fn last_node(&mut self) -> Option<Node> {
68        if self.is_empty() {
69            None
70        } else {
71            Some(Node(self.items.len() - 1))
72        }
73    }
74
75    pub fn len(&self) -> usize {
76        self.items.len()
77    }
78
79    pub fn is_empty(&self) -> bool {
80        self.items.is_empty()
81    }
82
83    pub fn new() -> Self {
84        Arena {
85            items: vec![],
86            version: ARENA_VERSION.fetch_add(1),
87        }
88    }
89
90    pub fn with_capacity(cap: usize) -> Self {
91        Arena {
92            items: Vec::with_capacity(cap),
93            version: ARENA_VERSION.fetch_add(1),
94        }
95    }
96
97    pub fn get_node(&self, val: &T) -> Option<Node> {
98        index_of(&self.items, val).map(Node)
99    }
100
101    pub fn swap(&mut self, idx_a: Node, idx_b: Node) {
102        self.items.swap(idx_a.0, idx_b.0)
103    }
104
105    #[inline]
106    pub fn get(&self, idx: Node) -> &T {
107        self.items.get(idx.0).unwrap()
108    }
109
110    #[inline]
111    /// # Safety
112    /// Doesn't do any bound checks
113    pub unsafe fn get_unchecked(&self, idx: Node) -> &T {
114        unsafe { self.items.get_unchecked(idx.0) }
115    }
116
117    #[inline]
118    pub fn get_mut(&mut self, idx: Node) -> &mut T {
119        self.items.get_mut(idx.0).unwrap()
120    }
121
122    #[inline]
123    /// Get mutable references to several items of the Arena
124    ///
125    /// The `idxs` is asserted to contain unique `Node` elements which are preferably (not
126    /// necessarily) in order.
127    pub fn get_many_mut<const N: usize>(&mut self, indices: [Node; N]) -> [&mut T; N] {
128        // @NOTE: This implementation is adapted from the Rust Nightly Standard Library. When
129        // `get_many_mut` gets stabilized we should use that.
130
131        let len = self.items.len();
132
133        // NB: The optimizer should inline the loops into a sequence
134        // of instructions without additional branching.
135        let mut valid = true;
136        for (i, &idx) in indices.iter().enumerate() {
137            valid &= idx.0 < len;
138            for &idx2 in &indices[..i] {
139                valid &= idx != idx2;
140            }
141        }
142
143        assert!(valid, "Duplicate index or out-of-bounds index");
144
145        // NB: This implementation is written as it is because any variation of
146        // `indices.map(|i| self.get_unchecked_mut(i))` would make miri unhappy,
147        // or generate worse code otherwise. This is also why we need to go
148        // through a raw pointer here.
149        let slice: *mut [T] = &mut self.items[..] as *mut _;
150        let mut arr: std::mem::MaybeUninit<[&mut T; N]> = std::mem::MaybeUninit::uninit();
151        let arr_ptr = arr.as_mut_ptr();
152
153        // SAFETY: We expect `indices` to contain disjunct values that are
154        // in bounds of `self`.
155        unsafe {
156            for i in 0..N {
157                let idx = *indices.get_unchecked(i);
158                let slice_ref: &mut [T] = &mut *slice;
159                *(*arr_ptr).get_unchecked_mut(i) = slice_ref.get_unchecked_mut(idx.0);
160            }
161            arr.assume_init()
162        }
163    }
164
165    #[inline]
166    pub fn replace(&mut self, idx: Node, val: T) -> T {
167        let x = self.get_mut(idx);
168        std::mem::replace(x, val)
169    }
170
171    pub fn clear(&mut self) {
172        self.items.clear();
173        self.version = ARENA_VERSION.fetch_add(1);
174    }
175}
176
177impl<T: Clone> Arena<T> {
178    pub fn duplicate(&mut self, node: Node) -> Node {
179        let item = self.items[node.0].clone();
180        self.add(item)
181    }
182}
183
184impl<T: Default> Arena<T> {
185    #[inline]
186    pub fn take(&mut self, idx: Node) -> T {
187        std::mem::take(self.get_mut(idx))
188    }
189
190    pub fn replace_with<F>(&mut self, idx: Node, f: F)
191    where
192        F: FnOnce(T) -> T,
193    {
194        let val = self.take(idx);
195        self.replace(idx, f(val));
196    }
197
198    pub fn try_replace_with<F>(&mut self, idx: Node, mut f: F) -> Result<()>
199    where
200        F: FnMut(T) -> Result<T>,
201    {
202        let val = self.take(idx);
203        self.replace(idx, f(val)?);
204        Ok(())
205    }
206}
polars_utils/arena.rs

polars_utils/
arena.rs
