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    extern crate ultrasonic_irq;

    use std::mem::transmute;
    use std::ptr::null_mut;
    use std::sync::atomic::Ordering;

    use self::ultrasonic_irq::Ultrasonic;

    /// Constructs a new `Ultrasonic` on heap and returns pointer.
    #[no_mangle]
    pub extern "C" fn ultrasonic_init(trigger: u8, echo: u8, temperature: u8) -> *mut Ultrasonic {
        match Ultrasonic::new(trigger, echo, temperature) {
            Err(_) => null_mut(),
            Ok(ultrasonic) => unsafe { transmute(Box::new(ultrasonic)) },
        }
    }

    /// Drops a `Ultrasonic` pointer on heap.
    #[no_mangle]
    pub extern "C" fn ultrasonic_clean(ultrasonic: *mut Ultrasonic) {
        let _ultrasonic: Box<Ultrasonic> = unsafe { transmute(ultrasonic) };
    }

    /// Returns `Ultrasonic` pointer distance.
    #[no_mangle]
    pub extern "C" fn ultrasonic_get_distance(ultrasonic: *mut Ultrasonic) -> u32 {
        let ultrasonic = unsafe { &mut *ultrasonic };

        ultrasonic.distance.load(Ordering::Relaxed)
    }

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