1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
use std::marker::PhantomData;
use std::ops::{Index, IndexMut};
use std::{fmt, slice};

use crate::{Idx, IndexVec};

/// A view into contiguous `T`s, indexed by `I` rather than by `usize`.
///
/// One common pattern you'll see is code that uses [`IndexVec::from_elem`]
/// to create the storage needed for a particular "universe" (aka the set of all
/// the possible keys that need an associated value) then passes that working
/// area as `&mut IndexSlice<I, T>` to clarify that nothing will be added nor
/// removed during processing (and, as a bonus, to chase fewer pointers).
#[derive(PartialEq, Eq, Hash)]
#[repr(transparent)]
pub struct IndexSlice<I: Idx, T> {
    _marker: PhantomData<fn(&I)>,
    pub raw: [T],
}

impl<I: Idx, T> IndexSlice<I, T> {
    #[inline]
    pub const fn empty() -> &'static Self {
        Self::from_raw(&[])
    }

    #[inline]
    pub const fn from_raw(raw: &[T]) -> &Self {
        let ptr: *const [T] = raw;
        // SAFETY: `IndexSlice` is `repr(transparent)` over a normal slice
        unsafe { &*(ptr as *const Self) }
    }

    #[inline]
    pub fn from_raw_mut(raw: &mut [T]) -> &mut Self {
        let ptr: *mut [T] = raw;
        // SAFETY: `IndexSlice` is `repr(transparent)` over a normal slice
        unsafe { &mut *(ptr as *mut Self) }
    }

    #[inline]
    pub const fn len(&self) -> usize {
        self.raw.len()
    }

    #[inline]
    pub const fn is_empty(&self) -> bool {
        self.raw.is_empty()
    }

    /// Gives the next index that will be assigned when `push` is called.
    ///
    /// Manual bounds checks can be done using `idx < slice.next_index()`
    /// (as opposed to `idx.index() < slice.len()`).
    #[inline]
    pub fn next_index(&self) -> I {
        I::new(self.len())
    }

    #[inline]
    pub fn iter(&self) -> slice::Iter<'_, T> {
        self.raw.iter()
    }

    #[inline]
    pub fn iter_enumerated(
        &self,
    ) -> impl DoubleEndedIterator<Item = (I, &T)> + ExactSizeIterator + '_ {
        self.raw.iter().enumerate().map(|(n, t)| (I::new(n), t))
    }

    #[inline]
    pub fn indices(
        &self,
    ) -> impl DoubleEndedIterator<Item = I> + ExactSizeIterator + Clone + 'static {
        (0..self.len()).map(|n| I::new(n))
    }

    #[inline]
    pub fn iter_mut(&mut self) -> slice::IterMut<'_, T> {
        self.raw.iter_mut()
    }

    #[inline]
    pub fn iter_enumerated_mut(
        &mut self,
    ) -> impl DoubleEndedIterator<Item = (I, &mut T)> + ExactSizeIterator + '_ {
        self.raw.iter_mut().enumerate().map(|(n, t)| (I::new(n), t))
    }

    #[inline]
    pub fn last_index(&self) -> Option<I> {
        self.len().checked_sub(1).map(I::new)
    }

    #[inline]
    pub fn swap(&mut self, a: I, b: I) {
        self.raw.swap(a.index(), b.index())
    }

    #[inline]
    pub fn get(&self, index: I) -> Option<&T> {
        self.raw.get(index.index())
    }

    #[inline]
    pub fn get_mut(&mut self, index: I) -> Option<&mut T> {
        self.raw.get_mut(index.index())
    }

    /// Returns mutable references to two distinct elements, `a` and `b`.
    ///
    /// Panics if `a == b`.
    #[inline]
    pub fn pick2_mut(&mut self, a: I, b: I) -> (&mut T, &mut T) {
        let (ai, bi) = (a.index(), b.index());
        assert!(ai != bi);

        if ai < bi {
            let (c1, c2) = self.raw.split_at_mut(bi);
            (&mut c1[ai], &mut c2[0])
        } else {
            let (c2, c1) = self.pick2_mut(b, a);
            (c1, c2)
        }
    }

    /// Returns mutable references to three distinct elements.
    ///
    /// Panics if the elements are not distinct.
    #[inline]
    pub fn pick3_mut(&mut self, a: I, b: I, c: I) -> (&mut T, &mut T, &mut T) {
        let (ai, bi, ci) = (a.index(), b.index(), c.index());
        assert!(ai != bi && bi != ci && ci != ai);
        let len = self.raw.len();
        assert!(ai < len && bi < len && ci < len);
        let ptr = self.raw.as_mut_ptr();
        unsafe { (&mut *ptr.add(ai), &mut *ptr.add(bi), &mut *ptr.add(ci)) }
    }

    #[inline]
    pub fn binary_search(&self, value: &T) -> Result<I, I>
    where
        T: Ord,
    {
        match self.raw.binary_search(value) {
            Ok(i) => Ok(Idx::new(i)),
            Err(i) => Err(Idx::new(i)),
        }
    }
}

impl<I: Idx, J: Idx> IndexSlice<I, J> {
    /// Invert a bijective mapping, i.e. `invert(map)[y] = x` if `map[x] = y`,
    /// assuming the values in `self` are a permutation of `0..self.len()`.
    ///
    /// This is used to go between `memory_index` (source field order to memory order)
    /// and `inverse_memory_index` (memory order to source field order).
    /// See also `FieldsShape::Arbitrary::memory_index` for more details.
    // FIXME(eddyb) build a better abstraction for permutations, if possible.
    pub fn invert_bijective_mapping(&self) -> IndexVec<J, I> {
        debug_assert_eq!(
            self.iter().map(|x| x.index() as u128).sum::<u128>(),
            (0..self.len() as u128).sum::<u128>(),
            "The values aren't 0..N in input {self:?}",
        );

        let mut inverse = IndexVec::from_elem_n(Idx::new(0), self.len());
        for (i1, &i2) in self.iter_enumerated() {
            inverse[i2] = i1;
        }

        debug_assert_eq!(
            inverse.iter().map(|x| x.index() as u128).sum::<u128>(),
            (0..inverse.len() as u128).sum::<u128>(),
            "The values aren't 0..N in result {self:?}",
        );

        inverse
    }
}

impl<I: Idx, T: fmt::Debug> fmt::Debug for IndexSlice<I, T> {
    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
        fmt::Debug::fmt(&self.raw, fmt)
    }
}

impl<I: Idx, T> Index<I> for IndexSlice<I, T> {
    type Output = T;

    #[inline]
    fn index(&self, index: I) -> &T {
        &self.raw[index.index()]
    }
}

impl<I: Idx, T> IndexMut<I> for IndexSlice<I, T> {
    #[inline]
    fn index_mut(&mut self, index: I) -> &mut T {
        &mut self.raw[index.index()]
    }
}

impl<'a, I: Idx, T> IntoIterator for &'a IndexSlice<I, T> {
    type Item = &'a T;
    type IntoIter = slice::Iter<'a, T>;

    #[inline]
    fn into_iter(self) -> slice::Iter<'a, T> {
        self.raw.iter()
    }
}

impl<'a, I: Idx, T> IntoIterator for &'a mut IndexSlice<I, T> {
    type Item = &'a mut T;
    type IntoIter = slice::IterMut<'a, T>;

    #[inline]
    fn into_iter(self) -> slice::IterMut<'a, T> {
        self.raw.iter_mut()
    }
}

impl<I: Idx, T: Clone> ToOwned for IndexSlice<I, T> {
    type Owned = IndexVec<I, T>;

    fn to_owned(&self) -> IndexVec<I, T> {
        IndexVec::from_raw(self.raw.to_owned())
    }

    fn clone_into(&self, target: &mut IndexVec<I, T>) {
        self.raw.clone_into(&mut target.raw)
    }
}

impl<I: Idx, T> Default for &IndexSlice<I, T> {
    #[inline]
    fn default() -> Self {
        IndexSlice::from_raw(Default::default())
    }
}

impl<I: Idx, T> Default for &mut IndexSlice<I, T> {
    #[inline]
    fn default() -> Self {
        IndexSlice::from_raw_mut(Default::default())
    }
}

// Whether `IndexSlice` is `Send` depends only on the data,
// not the phantom data.
unsafe impl<I: Idx, T> Send for IndexSlice<I, T> where T: Send {}