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use crate::iter::plumbing::*;
use crate::iter::*;
use std::marker::PhantomData;
use std::{fmt, mem};
trait ChunkBySlice<T>: AsRef<[T]> + Default + Send {
fn split(self, index: usize) -> (Self, Self);
fn find(&self, pred: &impl Fn(&T, &T) -> bool, start: usize, end: usize) -> Option<usize> {
self.as_ref()[start..end]
.windows(2)
.position(move |w| !pred(&w[0], &w[1]))
.map(|i| i + 1)
}
fn rfind(&self, pred: &impl Fn(&T, &T) -> bool, end: usize) -> Option<usize> {
self.as_ref()[..end]
.windows(2)
.rposition(move |w| !pred(&w[0], &w[1]))
.map(|i| i + 1)
}
}
impl<T: Sync> ChunkBySlice<T> for &[T] {
fn split(self, index: usize) -> (Self, Self) {
self.split_at(index)
}
}
impl<T: Send> ChunkBySlice<T> for &mut [T] {
fn split(self, index: usize) -> (Self, Self) {
self.split_at_mut(index)
}
}
struct ChunkByProducer<'p, T, Slice, Pred> {
slice: Slice,
pred: &'p Pred,
tail: usize,
marker: PhantomData<fn(&T)>,
}
// Note: this implementation is very similar to `SplitProducer`.
impl<T, Slice, Pred> UnindexedProducer for ChunkByProducer<'_, T, Slice, Pred>
where
Slice: ChunkBySlice<T>,
Pred: Fn(&T, &T) -> bool + Send + Sync,
{
type Item = Slice;
fn split(self) -> (Self, Option<Self>) {
if self.tail < 2 {
return (Self { tail: 0, ..self }, None);
}
// Look forward for the separator, and failing that look backward.
let mid = self.tail / 2;
let index = match self.slice.find(self.pred, mid, self.tail) {
Some(i) => Some(mid + i),
None => self.slice.rfind(self.pred, mid + 1),
};
if let Some(index) = index {
let (left, right) = self.slice.split(index);
let (left_tail, right_tail) = if index <= mid {
// If we scanned backwards to find the separator, everything in
// the right side is exhausted, with no separators left to find.
(index, 0)
} else {
(mid + 1, self.tail - index)
};
// Create the left split before the separator.
let left = Self {
slice: left,
tail: left_tail,
..self
};
// Create the right split following the separator.
let right = Self {
slice: right,
tail: right_tail,
..self
};
(left, Some(right))
} else {
// The search is exhausted, no more separators...
(Self { tail: 0, ..self }, None)
}
}
fn fold_with<F>(self, mut folder: F) -> F
where
F: Folder<Self::Item>,
{
let Self {
slice, pred, tail, ..
} = self;
let (slice, tail) = if tail == slice.as_ref().len() {
// No tail section, so just let `consume_iter` do it all.
(Some(slice), None)
} else if let Some(index) = slice.rfind(pred, tail) {
// We found the last separator to complete the tail, so
// end with that slice after `consume_iter` finds the rest.
let (left, right) = slice.split(index);
(Some(left), Some(right))
} else {
// We know there are no separators at all, so it's all "tail".
(None, Some(slice))
};
if let Some(mut slice) = slice {
// TODO (MSRV 1.77) use either:
// folder.consume_iter(slice.chunk_by(pred))
// folder.consume_iter(slice.chunk_by_mut(pred))
folder = folder.consume_iter(std::iter::from_fn(move || {
let len = slice.as_ref().len();
if len > 0 {
let i = slice.find(pred, 0, len).unwrap_or(len);
let (head, tail) = mem::take(&mut slice).split(i);
slice = tail;
Some(head)
} else {
None
}
}));
}
if let Some(tail) = tail {
folder = folder.consume(tail);
}
folder
}
}
/// Parallel iterator over slice in (non-overlapping) chunks separated by a predicate.
///
/// This struct is created by the [`par_chunk_by`] method on `&[T]`.
///
/// [`par_chunk_by`]: trait.ParallelSlice.html#method.par_chunk_by
pub struct ChunkBy<'data, T, P> {
pred: P,
slice: &'data [T],
}
impl<'data, T, P: Clone> Clone for ChunkBy<'data, T, P> {
fn clone(&self) -> Self {
ChunkBy {
pred: self.pred.clone(),
slice: self.slice,
}
}
}
impl<'data, T: fmt::Debug, P> fmt::Debug for ChunkBy<'data, T, P> {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
f.debug_struct("ChunkBy")
.field("slice", &self.slice)
.finish()
}
}
impl<'data, T, P> ChunkBy<'data, T, P> {
pub(super) fn new(slice: &'data [T], pred: P) -> Self {
Self { pred, slice }
}
}
impl<'data, T, P> ParallelIterator for ChunkBy<'data, T, P>
where
T: Sync,
P: Fn(&T, &T) -> bool + Send + Sync,
{
type Item = &'data [T];
fn drive_unindexed<C>(self, consumer: C) -> C::Result
where
C: UnindexedConsumer<Self::Item>,
{
bridge_unindexed(
ChunkByProducer {
tail: self.slice.len(),
slice: self.slice,
pred: &self.pred,
marker: PhantomData,
},
consumer,
)
}
}
/// Parallel iterator over slice in (non-overlapping) mutable chunks
/// separated by a predicate.
///
/// This struct is created by the [`par_chunk_by_mut`] method on `&mut [T]`.
///
/// [`par_chunk_by_mut`]: trait.ParallelSliceMut.html#method.par_chunk_by_mut
pub struct ChunkByMut<'data, T, P> {
pred: P,
slice: &'data mut [T],
}
impl<'data, T: fmt::Debug, P> fmt::Debug for ChunkByMut<'data, T, P> {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
f.debug_struct("ChunkByMut")
.field("slice", &self.slice)
.finish()
}
}
impl<'data, T, P> ChunkByMut<'data, T, P> {
pub(super) fn new(slice: &'data mut [T], pred: P) -> Self {
Self { pred, slice }
}
}
impl<'data, T, P> ParallelIterator for ChunkByMut<'data, T, P>
where
T: Send,
P: Fn(&T, &T) -> bool + Send + Sync,
{
type Item = &'data mut [T];
fn drive_unindexed<C>(self, consumer: C) -> C::Result
where
C: UnindexedConsumer<Self::Item>,
{
bridge_unindexed(
ChunkByProducer {
tail: self.slice.len(),
slice: self.slice,
pred: &self.pred,
marker: PhantomData,
},
consumer,
)
}
}