You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: skipmap.rs
    path of file: ./repos/incubator-teaclave/common/rusty_leveldb_sgx/src
    
    the code of the file until where you have to start completion: use crate::cmp::{Cmp, MemtableKeyCmp};
use crate::types::LdbIterator;
use rand::rngs::StdRng;
use rand::{RngCore, SeedableRng};

use std::cell::RefCell;
use std::cmp::Ordering;
use std::mem::{replace, size_of};
use std::rc::Rc;

const MAX_HEIGHT: usize = 12;
const BRANCHING_FACTOR: u32 = 4;

/// A node in a skipmap contains links to the next node and others that are further away (skips);
/// `skips[0]` is the immediate element after, that is, the element contained in `next`.
struct Node {
    skips: Vec<Option<*mut Node>>,
    next: Option<Box<Node>>,
    key: Vec<u8>,
    value: Vec<u8>,
}

/// Implements the backing store for a `MemTable`. The important methods are `insert()` and
/// `contains()`; in order to get full key and value for an entry, use a `SkipMapIter` instance,
/// `seek()` to the key to look up (this is as fast as any lookup in a skip map), and then call
/// `current()`.
struct InnerSkipMap {
    head: Box<Node>,
    rand: StdRng,
    len: usize,
    // approximation of memory used.
    approx_mem: usize,
    cmp: Rc<Box<dyn Cmp>>,
}

pub struct SkipMap {
    map: Rc<RefCell<InnerSkipMap>>,
}

impl Skip
    
    fn get_greater_or_equal<'a>(&'a self, key: &[u8]) -> Option<&'a Node> {
        // Start at the highest skip link of the head node, and work down from there
        let mut current = self.head.as_ref() as *const Node;
        let mut level = self.head.skips.len() - 1;

        loop {
            unsafe {
                if let Some(next) = (*current).skips[level] {
                    let ord = self.cmp.cmp((*next).key.as_slice(), key);

                    match ord {
                        Ordering::Less => {
                            current = next;
                            continue;
                        }
                        Ordering::Equal => return Some(&(*next)),
                        Ordering::Greater => {
                            if level == 0 {
                                return Some(&(*next));
                            }
                        }
                    }
                }
            }
            if level == 0 {
                break;
            }
            level -= 1;
        }

        unsafe {
            if current.is_null() || current == self.head.as_ref() {
                return None;
            } else if self.cmp.cmp(&(*current).key, key) == Ordering::Less {
                return None;
            } else {
                return Some(&(*current));
            }
        }
    }