1use std::cmp::min;
2
3use super::plumbing::*;
4use super::*;
5use crate::math::div_round_up;
6
7/// `Chunks` is an iterator that groups elements of an underlying iterator.
8///
9/// This struct is created by the [`chunks()`] method on [`IndexedParallelIterator`]
10///
11/// [`chunks()`]: trait.IndexedParallelIterator.html#method.chunks
12/// [`IndexedParallelIterator`]: trait.IndexedParallelIterator.html
13#[must_use = "iterator adaptors are lazy and do nothing unless consumed"]
14#[derive(Debug, Clone)]
15pub struct Chunks<I>
16where
17 I: IndexedParallelIterator,
18{
19 size: usize,
20 i: I,
21}
22
23impl<I> Chunks<I>
24where
25 I: IndexedParallelIterator,
26{
27 /// Creates a new `Chunks` iterator
28 pub(super) fn new(i: I, size: usize) -> Self {
29 Chunks { i, size }
30 }
31}
32
33impl<I> ParallelIterator for Chunks<I>
34where
35 I: IndexedParallelIterator,
36{
37 type Item = Vec<I::Item>;
38
39 fn drive_unindexed<C>(self, consumer: C) -> C::Result
40 where
41 C: Consumer<Vec<I::Item>>,
42 {
43 bridge(self, consumer)
44 }
45
46 fn opt_len(&self) -> Option<usize> {
47 Some(self.len())
48 }
49}
50
51impl<I> IndexedParallelIterator for Chunks<I>
52where
53 I: IndexedParallelIterator,
54{
55 fn drive<C>(self, consumer: C) -> C::Result
56 where
57 C: Consumer<Self::Item>,
58 {
59 bridge(self, consumer)
60 }
61
62 fn len(&self) -> usize {
63 div_round_up(self.i.len(), self.size)
64 }
65
66 fn with_producer<CB>(self, callback: CB) -> CB::Output
67 where
68 CB: ProducerCallback<Self::Item>,
69 {
70 let len = self.i.len();
71 return self.i.with_producer(Callback {
72 size: self.size,
73 len,
74 callback,
75 });
76
77 struct Callback<CB> {
78 size: usize,
79 len: usize,
80 callback: CB,
81 }
82
83 impl<T, CB> ProducerCallback<T> for Callback<CB>
84 where
85 CB: ProducerCallback<Vec<T>>,
86 {
87 type Output = CB::Output;
88
89 fn callback<P>(self, base: P) -> CB::Output
90 where
91 P: Producer<Item = T>,
92 {
93 let producer = ChunkProducer::new(self.size, self.len, base, Vec::from_iter);
94 self.callback.callback(producer)
95 }
96 }
97 }
98}
99
100pub(super) struct ChunkProducer<P, F> {
101 chunk_size: usize,
102 len: usize,
103 base: P,
104 map: F,
105}
106
107impl<P, F> ChunkProducer<P, F> {
108 pub(super) fn new(chunk_size: usize, len: usize, base: P, map: F) -> Self {
109 Self {
110 chunk_size,
111 len,
112 base,
113 map,
114 }
115 }
116}
117
118impl<P, F, T> Producer for ChunkProducer<P, F>
119where
120 P: Producer,
121 F: Fn(P::IntoIter) -> T + Send + Clone,
122{
123 type Item = T;
124 type IntoIter = std::iter::Map<ChunkSeq<P>, F>;
125
126 fn into_iter(self) -> Self::IntoIter {
127 let chunks = ChunkSeq {
128 chunk_size: self.chunk_size,
129 len: self.len,
130 inner: if self.len > 0 { Some(self.base) } else { None },
131 };
132 chunks.map(self.map)
133 }
134
135 fn split_at(self, index: usize) -> (Self, Self) {
136 let elem_index = min(index * self.chunk_size, self.len);
137 let (left, right) = self.base.split_at(elem_index);
138 (
139 ChunkProducer {
140 chunk_size: self.chunk_size,
141 len: elem_index,
142 base: left,
143 map: self.map.clone(),
144 },
145 ChunkProducer {
146 chunk_size: self.chunk_size,
147 len: self.len - elem_index,
148 base: right,
149 map: self.map,
150 },
151 )
152 }
153
154 fn min_len(&self) -> usize {
155 div_round_up(self.base.min_len(), self.chunk_size)
156 }
157
158 fn max_len(&self) -> usize {
159 self.base.max_len() / self.chunk_size
160 }
161}
162
163pub(super) struct ChunkSeq<P> {
164 chunk_size: usize,
165 len: usize,
166 inner: Option<P>,
167}
168
169impl<P> Iterator for ChunkSeq<P>
170where
171 P: Producer,
172{
173 type Item = P::IntoIter;
174
175 fn next(&mut self) -> Option<Self::Item> {
176 let producer = self.inner.take()?;
177 if self.len > self.chunk_size {
178 let (left, right) = producer.split_at(self.chunk_size);
179 self.inner = Some(right);
180 self.len -= self.chunk_size;
181 Some(left.into_iter())
182 } else {
183 debug_assert!(self.len > 0);
184 self.len = 0;
185 Some(producer.into_iter())
186 }
187 }
188
189 fn size_hint(&self) -> (usize, Option<usize>) {
190 let len = self.len();
191 (len, Some(len))
192 }
193}
194
195impl<P> ExactSizeIterator for ChunkSeq<P>
196where
197 P: Producer,
198{
199 #[inline]
200 fn len(&self) -> usize {
201 div_round_up(self.len, self.chunk_size)
202 }
203}
204
205impl<P> DoubleEndedIterator for ChunkSeq<P>
206where
207 P: Producer,
208{
209 fn next_back(&mut self) -> Option<Self::Item> {
210 let producer = self.inner.take()?;
211 if self.len > self.chunk_size {
212 let mut size = self.len % self.chunk_size;
213 if size == 0 {
214 size = self.chunk_size;
215 }
216 let (left, right) = producer.split_at(self.len - size);
217 self.inner = Some(left);
218 self.len -= size;
219 Some(right.into_iter())
220 } else {
221 debug_assert!(self.len > 0);
222 self.len = 0;
223 Some(producer.into_iter())
224 }
225 }
226}
227