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/*!
 * The Cythan machine emulator librairy.
 * 
 * The Cythan machine is a mathematical Turing Complete computer.
 * The machine is composed of one vector. Each value of the vector is a positive integer, "pointing" to another value.
 * 
 * ### For every iteration of the machine
 * 
 *  - The first case (the pointer), is incremented by 2.
 * 
 *  - The 2 cases pointed by the first case before the incrementation is "executed". In a pair of executed cases, the case that as for index the second value is set to the value of the case that have as index the first value
 * 
 * For instance, `1,5,3,0,0,999` will copy the content of the 5th case (999) into the 3rd one. The result after one iteration will be `3,5,3,999,0,999`
 * 
 * ### Example
 * 
 * ```rust
 * use cythan::Cythan;
 * let mut cythan = Cythan::new( vec![1,9,5,10,1,0,0,11,0,1,20,21] );
 * println!("Cythan start:{:?}",cythan);
 * for a in 0..10 {
 *    cythan.next();
 *    println!("Cythan iteration {}:{:?}",a,cythan)
 * }
 * ```
 * 
*/





#![cfg_attr(feature = "nightly", feature(test))]

#[cfg(feature = "nightly")]
extern crate test;

#[cfg(feature = "nightly")]
use test::Bencher;

/// The main structure of the Cythan machine
#[derive(Debug)]
pub struct Cythan {
    cases: Vec<usize>
}


impl Cythan{
    /// The constructor of the Cythan machine
    /// `cases` is a vector that represent the base code of the Cythan machine
    /// ### Example
    /// ```rust
    /// use cythan::Cythan;
    /// let mut cythan = Cythan::new( vec![1,9,5,10,1,0,0,11,0,1,20,21] );
    /// println!("Cythan start:{:?}",cythan);
    /// for a in 0..10 {
    ///    cythan.next();
    ///    println!("Cythan iteration {}:{:?}",a,cythan)
    /// }
    /// ```
    /// will make an if statement in Cythan, which will jump the pointer to either 20 or 21 accordingly if the 9th case contains an one or a zero.
    pub fn new(cases: Vec<usize>) -> Cythan {
        Cythan{
            cases
        }
    }

    /// Will execute one iteration of the Cythan machine.
    /// This method use a step of 2.
    #[inline]
    pub fn next(&mut self) {
        unsafe {
            let index = {
                let index = self.get_mut_value(0);
                *index += 2;
                *index
            };

            let (c2,c1) = self.get_both_values(index-2);
    
            self.set_value(c1,self.get_value(c2));
        }
    }

    #[inline]
    fn get_both_values(&self, index: usize) -> (usize,usize) {
        let mut i = self.cases.iter().skip(index);
        (*i.next().unwrap_or(&0),*i.next().unwrap_or(&0))
    }

    /// Use this to get a value at an index in the Cythan machine.
    /// This will return 0 if the index doesn't exists.
    #[inline]
    pub fn get_value(&self, index:usize) -> usize {
        *self.cases.get(index).unwrap_or(&0)
    }

    #[inline]
    unsafe fn get_mut_value(&mut self, index:usize) -> &mut usize {
        if self.cases.len() <= index {
            self.cases.extend((self.cases.len()..index+1).map(|_| 0)); 
        }
        self.cases.get_unchecked_mut(index)
    }

    /// Use this to set a value at an index inside of th Cythan machine.
    /// This will fill the machine with 0 if the index doesn't exists.
    #[inline]
    pub fn set_value(&mut self, index:usize, value:usize) {
        if self.cases.len() <= index {
            self.cases.extend((self.cases.len()..index).map(|_| 0)); 
            self.cases.push(value);
        } else {
            unsafe {
                *self.cases.get_unchecked_mut(index) = value;
            }
        }
    }
}

#[cfg(feature = "nightly")]
#[bench]
fn bench(b: &mut Bencher) {
    let mut cythan = Cythan::new( vec![1,9,5,10,1,0,0,11,0,1,20,21] );
    b.iter(||{
        cythan.next()
    });
    println!("{:?}",cythan);
}