# linked_list.rs - source
Source of the Rust file `/home/runner/.cargo/registry/src/github.com-1ecc6299db9ec823/buddy_system_allocator-0.6.0/src/linked_list.rs`.
Keywords: rust, rustlang, rust-lang

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    //! Provide the intrusive LinkedList
    #![allow(dead_code)]

    use core::{fmt, ptr};

    /// An intrusive linked list
    ///
    /// A clean room implementation of the one used in CS140e 2018 Winter
    ///
    /// Thanks Sergio Benitez for his excellent work,
    /// See [CS140e](https://cs140e.sergio.bz/) for more information
    #[derive(Copy, Clone)]
    pub struct LinkedList {
        head: *mut usize,
    }

    unsafe impl Send for LinkedList {}

    impl LinkedList {
        /// Create a new LinkedList
        pub const fn new() -> LinkedList {
            LinkedList {
                head: ptr::null_mut(),
            }
        }

        /// Return `true` if the list is empty
        pub fn is_empty(&self) -> bool {
            self.head.is_null()
        }

        /// Push `item` to the front of the list
        pub unsafe fn push(&mut self, item: *mut usize) {
            *item = self.head as usize;
            self.head = item;
        }

        /// Try to remove the first item in the list
        pub fn pop(&mut self) -> Option<*mut usize> {
            match self.is_empty() {
                true => None,
                false => {
                    // Advance head pointer
                    let item = self.head;
                    self.head = unsafe { *item as *mut usize };
                    Some(item)
                }
            }
        }

        /// Return an iterator over the items in the list
        pub fn iter(&self) -> Iter {
            Iter {
                curr: self.head,
                list: self,
            }
        }

        /// Return an mutable iterator over the items in the list
        pub fn iter_mut(&mut self) -> IterMut {
            IterMut {
                prev: &mut self.head as *mut *mut usize as *mut usize,
                curr: self.head,
                list: self,
            }
        }
    }

    impl fmt::Debug for LinkedList {
        fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
            f.debug_list().entries(self.iter()).finish()
        }
    }

    /// An iterator over the linked list
    pub struct Iter<'a> {
        curr: *mut usize,
        list: &'a LinkedList,
    }

    impl<'a> Iterator for Iter<'a> {
        type Item = *mut usize;

        fn next(&mut self) -> Option<Self::Item> {
            if self.curr.is_null() {
                None
            } else {
                let item = self.curr;
                let next = unsafe { *item as *mut usize };
                self.curr = next;
                Some(item)
            }
        }
    }

    /// Represent a mutable node in `LinkedList`
    pub struct ListNode {
        prev: *mut usize,
        curr: *mut usize,
    }

    impl ListNode {
        /// Remove the node from the list
        pub fn pop(self) -> *mut usize {
            // Skip the current one
            unsafe {
                *(self.prev) = *(self.curr);
            }
            self.curr
        }

        /// Returns the pointed address
        pub fn value(&self) -> *mut usize {
            self.curr
        }
    }

    /// A mutable iterator over the linked list
    pub struct IterMut<'a> {
        list: &'a mut LinkedList,
        prev: *mut usize,
        curr: *mut usize,
    }

    impl<'a> Iterator for IterMut<'a> {
        type Item = ListNode;

        fn next(&mut self) -> Option<Self::Item> {
            if self.curr.is_null() {
                None
            } else {
                let res = ListNode {
                    prev: self.prev,
                    curr: self.curr,
                };
                self.prev = self.curr;
                self.curr = unsafe { *self.curr as *mut usize };
                Some(res)
            }
        }
    }