From 041839ceabbc67165512fde0d33c91347b758487 Mon Sep 17 00:00:00 2001
From: Jakub Kotur <qtr@google.com>
Date: Mon, 21 Dec 2020 17:28:15 +0100
Subject: Initial import of rayon-1.5.0.

Bug: 155309706
Change-Id: I6ff7de1cb89d093d7938abf78d586ed76da85b0d
---
 src/iter/enumerate.rs | 133 ++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 133 insertions(+)
 create mode 100644 src/iter/enumerate.rs

(limited to 'src/iter/enumerate.rs')

diff --git a/src/iter/enumerate.rs b/src/iter/enumerate.rs
new file mode 100644
index 0000000..980ee7c
--- /dev/null
+++ b/src/iter/enumerate.rs
@@ -0,0 +1,133 @@
+use super::plumbing::*;
+use super::*;
+use std::iter;
+use std::ops::Range;
+use std::usize;
+
+/// `Enumerate` is an iterator that returns the current count along with the element.
+/// This struct is created by the [`enumerate()`] method on [`IndexedParallelIterator`]
+///
+/// [`enumerate()`]: trait.IndexedParallelIterator.html#method.enumerate
+/// [`IndexedParallelIterator`]: trait.IndexedParallelIterator.html
+#[must_use = "iterator adaptors are lazy and do nothing unless consumed"]
+#[derive(Debug, Clone)]
+pub struct Enumerate<I: IndexedParallelIterator> {
+    base: I,
+}
+
+impl<I> Enumerate<I>
+where
+    I: IndexedParallelIterator,
+{
+    /// Creates a new `Enumerate` iterator.
+    pub(super) fn new(base: I) -> Self {
+        Enumerate { base }
+    }
+}
+
+impl<I> ParallelIterator for Enumerate<I>
+where
+    I: IndexedParallelIterator,
+{
+    type Item = (usize, I::Item);
+
+    fn drive_unindexed<C>(self, consumer: C) -> C::Result
+    where
+        C: UnindexedConsumer<Self::Item>,
+    {
+        bridge(self, consumer)
+    }
+
+    fn opt_len(&self) -> Option<usize> {
+        Some(self.len())
+    }
+}
+
+impl<I> IndexedParallelIterator for Enumerate<I>
+where
+    I: IndexedParallelIterator,
+{
+    fn drive<C: Consumer<Self::Item>>(self, consumer: C) -> C::Result {
+        bridge(self, consumer)
+    }
+
+    fn len(&self) -> usize {
+        self.base.len()
+    }
+
+    fn with_producer<CB>(self, callback: CB) -> CB::Output
+    where
+        CB: ProducerCallback<Self::Item>,
+    {
+        return self.base.with_producer(Callback { callback });
+
+        struct Callback<CB> {
+            callback: CB,
+        }
+
+        impl<I, CB> ProducerCallback<I> for Callback<CB>
+        where
+            CB: ProducerCallback<(usize, I)>,
+        {
+            type Output = CB::Output;
+            fn callback<P>(self, base: P) -> CB::Output
+            where
+                P: Producer<Item = I>,
+            {
+                let producer = EnumerateProducer { base, offset: 0 };
+                self.callback.callback(producer)
+            }
+        }
+    }
+}
+
+/// ////////////////////////////////////////////////////////////////////////
+/// Producer implementation
+
+struct EnumerateProducer<P> {
+    base: P,
+    offset: usize,
+}
+
+impl<P> Producer for EnumerateProducer<P>
+where
+    P: Producer,
+{
+    type Item = (usize, P::Item);
+    type IntoIter = iter::Zip<Range<usize>, P::IntoIter>;
+
+    fn into_iter(self) -> Self::IntoIter {
+        // Enumerate only works for IndexedParallelIterators. Since those
+        // have a max length of usize::MAX, their max index is
+        // usize::MAX - 1, so the range 0..usize::MAX includes all
+        // possible indices.
+        //
+        // However, we should to use a precise end to the range, otherwise
+        // reversing the iterator may have to walk back a long ways before
+        // `Zip::next_back` can produce anything.
+        let base = self.base.into_iter();
+        let end = self.offset + base.len();
+        (self.offset..end).zip(base)
+    }
+
+    fn min_len(&self) -> usize {
+        self.base.min_len()
+    }
+    fn max_len(&self) -> usize {
+        self.base.max_len()
+    }
+
+    fn split_at(self, index: usize) -> (Self, Self) {
+        let (left, right) = self.base.split_at(index);
+        (
+            EnumerateProducer {
+                base: left,
+                offset: self.offset,
+            },
+            EnumerateProducer {
+                base: right,
+                offset: self.offset + index,
+            },
+        )
+    }
+}
-- 
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