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    use crate::{memchr, memchr2, memchr3, memrchr, memrchr2, memrchr3};

    macro_rules! iter_next {
        // Common code for the memchr iterators:
        // update haystack and position and produce the index
        //
        // self: &mut Self where Self is the iterator
        // search_result: Option<usize> which is the result of the corresponding
        // memchr function.
        //
        // Returns Option<usize> (the next iterator element)
        ($self_:expr, $search_result:expr) => {
            $search_result.map(move |index| {
                // split and take the remaining back half
                $self_.haystack = $self_.haystack.split_at(index + 1).1;
                let found_position = $self_.position + index;
                $self_.position = found_position + 1;
                found_position
            })
        };
    }

    macro_rules! iter_next_back {
        ($self_:expr, $search_result:expr) => {
            $search_result.map(move |index| {
                // split and take the remaining front half
                $self_.haystack = $self_.haystack.split_at(index).0;
                $self_.position + index
            })
        };
    }

    /// An iterator for `memchr`.
    pub struct Memchr<'a> {
        needle: u8,
        // The haystack to iterate over
        haystack: &'a [u8],
        // The index
        position: usize,
    }

    impl<'a> Memchr<'a> {
        /// Creates a new iterator that yields all positions of needle in haystack.
        #[inline]
        pub fn new(needle: u8, haystack: &[u8]) -> Memchr<'_> {
            Memchr { needle: needle, haystack: haystack, position: 0 }
        }
    }

    impl<'a> Iterator for Memchr<'a> {
        type Item = usize;

        #[inline]
        fn next(&mut self) -> Option<usize> {
            iter_next!(self, memchr(self.needle, self.haystack))
        }

        #[inline]
        fn size_hint(&self) -> (usize, Option<usize>) {
            (0, Some(self.haystack.len()))
        }
    }

    impl<'a> DoubleEndedIterator for Memchr<'a> {
        #[inline]
        fn next_back(&mut self) -> Option<Self::Item> {
            iter_next_back!(self, memrchr(self.needle, self.haystack))
        }
    }

    /// An iterator for `memchr2`.
    pub struct Memchr2<'a> {
        needle1: u8,
        needle2: u8,
        // The haystack to iterate over
        haystack: &'a [u8],
        // The index
        position: usize,
    }

    impl<'a> Memchr2<'a> {
        /// Creates a new iterator that yields all positions of needle in haystack.
        #[inline]
        pub fn new(needle1: u8, needle2: u8, haystack: &[u8]) -> Memchr2<'_> {
            Memchr2 {
                needle1: needle1,
                needle2: needle2,
                haystack: haystack,
                position: 0,
            }
        }
    }

    impl<'a> Iterator for Memchr2<'a> {
        type Item = usize;

        #[inline]
        fn next(&mut self) -> Option<usize> {
            iter_next!(self, memchr2(self.needle1, self.needle2, self.haystack))
        }

        #[inline]
        fn size_hint(&self) -> (usize, Option<usize>) {
            (0, Some(self.haystack.len()))
        }
    }

    impl<'a> DoubleEndedIterator for Memchr2<'a> {
        #[inline]
        fn next_back(&mut self) -> Option<Self::Item> {
            iter_next_back!(
                self,
                memrchr2(self.needle1, self.needle2, self.haystack)
            )
        }
    }

    /// An iterator for `memchr3`.
    pub struct Memchr3<'a> {
        needle1: u8,
        needle2: u8,
        needle3: u8,
        // The haystack to iterate over
        haystack: &'a [u8],
        // The index
        position: usize,
    }

    impl<'a> Memchr3<'a> {
        /// Create a new `Memchr3` that's initialized to zero with a haystack
        #[inline]
        pub fn new(
            needle1: u8,
            needle2: u8,
            needle3: u8,
            haystack: &[u8],
        ) -> Memchr3<'_> {
            Memchr3 {
                needle1: needle1,
                needle2: needle2,
                needle3: needle3,
                haystack: haystack,
                position: 0,
            }
        }
    }

    impl<'a> Iterator for Memchr3<'a> {
        type Item = usize;

        #[inline]
        fn next(&mut self) -> Option<usize> {
            iter_next!(
                self,
                memchr3(self.needle1, self.needle2, self.needle3, self.haystack)
            )
        }

        #[inline]
        fn size_hint(&self) -> (usize, Option<usize>) {
            (0, Some(self.haystack.len()))
        }
    }

    impl<'a> DoubleEndedIterator for Memchr3<'a> {
        #[inline]
        fn next_back(&mut self) -> Option<Self::Item> {
            iter_next_back!(
                self,
                memrchr3(self.needle1, self.needle2, self.needle3, self.haystack)
            )
        }
    }