hll.rs

use std::hash::*;
use std::marker::PhantomData;

//Lazy hyper log log implementation
pub struct HyperLogLog<const N: usize, T: Hash> {
    regs: [u64; N],
    //enforce homogenuiy
    //no homo...
    phantom: PhantomData<T>,
}

impl<const N: usize, T: Hash> HyperLogLog<N, T> {

    pub fn cardinality(&self) -> u64 {
        //get harmonic mean
        let mut sum = 0.0;

        for reg in self.regs.iter() {
            sum += 1.0 / (1 << reg.leading_zeros()) as f64;
        }

        let mean = N as f64 / sum;
        u64::pow(2, N as u32 * mean as u32)
    }

    pub fn add(&mut self, elem: &T) {
            //hash the result in it's respective register
            let mut hasher = DefaultHasher::new();
            elem.hash(&mut hasher);
            let hash = hasher.finish();
    }
}