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diff --git a/vendor/itertools/benches/extra/zipslices.rs b/vendor/itertools/benches/extra/zipslices.rs
new file mode 100644
index 000000000..8bf3967f5
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+++ b/vendor/itertools/benches/extra/zipslices.rs
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+use std::cmp;
+
+// Note: There are different ways to implement ZipSlices.
+// This version performed the best in benchmarks.
+//
+// I also implemented a version with three pointes (tptr, tend, uptr),
+// that mimiced slice::Iter and only checked bounds by using tptr == tend,
+// but that was inferior to this solution.
+
+/// An iterator which iterates two slices simultaneously.
+///
+/// `ZipSlices` acts like a double-ended `.zip()` iterator.
+///
+/// It was intended to be more efficient than `.zip()`, and it was, then
+/// rustc changed how it optimizes so it can not promise improved performance
+/// at this time.
+///
+/// Note that elements past the end of the shortest of the two slices are ignored.
+///
+/// Iterator element type for `ZipSlices<T, U>` is `(T::Item, U::Item)`. For example,
+/// for a `ZipSlices<&'a [A], &'b mut [B]>`, the element type is `(&'a A, &'b mut B)`.
+#[derive(Clone)]
+pub struct ZipSlices<T, U> {
+    t: T,
+    u: U,
+    len: usize,
+    index: usize,
+}
+
+impl<'a, 'b, A, B> ZipSlices<&'a [A], &'b [B]> {
+    /// Create a new `ZipSlices` from slices `a` and `b`.
+    ///
+    /// Act like a double-ended `.zip()` iterator, but more efficiently.
+    ///
+    /// Note that elements past the end of the shortest of the two slices are ignored.
+    #[inline(always)]
+    pub fn new(a: &'a [A], b: &'b [B]) -> Self {
+        let minl = cmp::min(a.len(), b.len());
+        ZipSlices {
+            t: a,
+            u: b,
+            len: minl,
+            index: 0,
+        }
+    }
+}
+
+impl<T, U> ZipSlices<T, U>
+    where T: Slice,
+          U: Slice
+{
+    /// Create a new `ZipSlices` from slices `a` and `b`.
+    ///
+    /// Act like a double-ended `.zip()` iterator, but more efficiently.
+    ///
+    /// Note that elements past the end of the shortest of the two slices are ignored.
+    #[inline(always)]
+    pub fn from_slices(a: T, b: U) -> Self {
+        let minl = cmp::min(a.len(), b.len());
+        ZipSlices {
+            t: a,
+            u: b,
+            len: minl,
+            index: 0,
+        }
+    }
+}
+
+impl<T, U> Iterator for ZipSlices<T, U>
+    where T: Slice,
+          U: Slice
+{
+    type Item = (T::Item, U::Item);
+
+    #[inline(always)]
+    fn next(&mut self) -> Option<Self::Item> {
+        unsafe {
+            if self.index >= self.len {
+                None
+            } else {
+                let i = self.index;
+                self.index += 1;
+                Some((
+                    self.t.get_unchecked(i),
+                    self.u.get_unchecked(i)))
+            }
+        }
+    }
+
+    #[inline]
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        let len = self.len - self.index;
+        (len, Some(len))
+    }
+}
+
+impl<T, U> DoubleEndedIterator for ZipSlices<T, U>
+    where T: Slice,
+          U: Slice
+{
+    #[inline(always)]
+    fn next_back(&mut self) -> Option<Self::Item> {
+        unsafe {
+            if self.index >= self.len {
+                None
+            } else {
+                self.len -= 1;
+                let i = self.len;
+                Some((
+                    self.t.get_unchecked(i),
+                    self.u.get_unchecked(i)))
+            }
+        }
+    }
+}
+
+impl<T, U> ExactSizeIterator for ZipSlices<T, U>
+    where T: Slice,
+          U: Slice
+{}
+
+unsafe impl<T, U> Slice for ZipSlices<T, U>
+    where T: Slice,
+          U: Slice
+{
+    type Item = (T::Item, U::Item);
+
+    fn len(&self) -> usize {
+        self.len - self.index
+    }
+
+    unsafe fn get_unchecked(&mut self, i: usize) -> Self::Item {
+        (self.t.get_unchecked(i),
+         self.u.get_unchecked(i))
+    }
+}
+
+/// A helper trait to let `ZipSlices` accept both `&[T]` and `&mut [T]`.
+///
+/// Unsafe trait because:
+///
+/// - Implementors must guarantee that `get_unchecked` is valid for all indices `0..len()`.
+pub unsafe trait Slice {
+    /// The type of a reference to the slice's elements
+    type Item;
+    #[doc(hidden)]
+    fn len(&self) -> usize;
+    #[doc(hidden)]
+    unsafe fn get_unchecked(&mut self, i: usize) -> Self::Item;
+}
+
+unsafe impl<'a, T> Slice for &'a [T] {
+    type Item = &'a T;
+    #[inline(always)]
+    fn len(&self) -> usize { (**self).len() }
+    #[inline(always)]
+    unsafe fn get_unchecked(&mut self, i: usize) -> &'a T {
+        debug_assert!(i < self.len());
+        (**self).get_unchecked(i)
+    }
+}
+
+unsafe impl<'a, T> Slice for &'a mut [T] {
+    type Item = &'a mut T;
+    #[inline(always)]
+    fn len(&self) -> usize { (**self).len() }
+    #[inline(always)]
+    unsafe fn get_unchecked(&mut self, i: usize) -> &'a mut T {
+        debug_assert!(i < self.len());
+        // override the lifetime constraints of &mut &'a mut [T]
+        (*(*self as *mut [T])).get_unchecked_mut(i)
+    }
+}
+
+#[test]
+fn zipslices() {
+
+    let xs = [1, 2, 3, 4, 5, 6];
+    let ys = [1, 2, 3, 7];
+    ::itertools::assert_equal(ZipSlices::new(&xs, &ys), xs.iter().zip(&ys));
+
+    let xs = [1, 2, 3, 4, 5, 6];
+    let mut ys = [0; 6];
+    for (x, y) in ZipSlices::from_slices(&xs[..], &mut ys[..]) {
+        *y = *x;
+    }
+    ::itertools::assert_equal(&xs, &ys);
+}