/* author Bill Wood */

fn sqrt(n: usize) -> usize {
    let (mut r1, mut r) = (n, n + 1);
    while r1 < r {
        r = r1;
        r1 = (r1 + n/r1) >> 1
    }
    r
}

struct SimpleSieve {
    primes: Vec<u32>,
}
impl SimpleSieve {
    fn new(high: usize) -> Self {
        assert_eq!(high | 1, high);
        let mut pvec = vec![false; (high + 1)/2];
        let mut primes = vec![];
        let n = high >> 1;
        let mut i = 3;
        while i*i <= high {
            if !pvec[i >> 1] {
                primes.push(i as u32);
                let mut j = (i*i) >> 1;
                while j <= n {
                    pvec[j] = true;
                    j += i;
                }
            }
            i += 2;
        }
        i >>= 1;
        while i <= n {
            if !pvec[i] {
                primes.push(((i << 1) | 1) as u32);
            }
            i += 1;
        }
        dbg!(primes.len());
        SimpleSieve { primes, }
    }
}

type CBFn<'a> = &'a mut dyn FnMut(usize);
struct SieveSlice<'a> {
    low: usize,
    high: usize,
    bslice: &'a mut [bool],
}
impl<'a> SieveSlice<'a> {
    fn new(low: usize, high: usize, bslice: &'a mut [bool]) -> Self {
        // assert_eq!(low | 1, low);
        // assert_eq!(high | 1, high);
        // dbg!(low, high, );
        SieveSlice { low, high, bslice }
    }
    fn find(&mut self, f: CBFn, sieve: &SimpleSieve) {
        let (low, high) = (self.low, self.high);

        // generate primes
        let n = (high + 2 - low) >> 1;
        for i in 0..sieve.primes.len() {
            let p = sieve.primes[i] as usize;
            let mut j = p*p;
            if j < low {
                j += (low - 1 - j + p*2)/2/p*p*2;
            }
            if j > high {//?? moved here
                break;
            }
            j = (j - low) >> 1;
            while j < n {
                self.bslice[j] = true;
                j += p;
            }
        }
        // callback primes
        if low < 2 && high > 2 {
            self.bslice[0] = true;   // 1 is not prime
            f(2);               // 2 is prime
        }
        for i in 0..n {
            if !self.bslice[i] {
                f((i << 1) + low);
            }
        }
    }
}

use rayon::prelude::*;
struct Primes {
    low: usize,
    high: usize,
    seg_size: usize,
    seg_num_chunks: usize,
}
impl Primes {
    fn new(mut low: usize, mut high: usize, seg_size_kb: usize, seg_num_chunks: usize) -> Result<Self, ()> {
        // lowest odd >= low
        low |= 1;
        if low > high || seg_size_kb == 0 || seg_num_chunks == 0 || seg_size_kb*1024 < seg_num_chunks {
            return Err(());
        }
        // highest odd <= high
        high = (high - 1) | 1;
        let seg_size = seg_size_kb.next_power_of_two()*1024;
        Ok(Primes { low, high, seg_size, seg_num_chunks })
    }
    fn callback(&self, f: CBFn) {
        let high = self.high;

        // x where x: odd and (x+2)^2 > high and x^2 < high
        let ss_high = (sqrt(high) - 1) | 1;
        let sieve = SimpleSieve::new(ss_high);

        // track odds only
        let seg_nprimes_per_byte = 2;

        let mut seg_low = self.low;
        dbg!(self.low, ss_high, seg_low, high, self.seg_num_chunks, self.seg_size, );
        let mut sieve_seg = vec![false; self.seg_size];
        let mut c = 0;
        while seg_low <= high {
            let mut segments = vec!();
            for bslice in sieve_seg.chunks_mut(self.seg_size/self.seg_num_chunks) {
                let mut seg_high = seg_low + bslice.len()*seg_nprimes_per_byte - 2;
                if seg_high > high {
                    seg_high = high;
                }
                segments.push(SieveSlice::new(seg_low, seg_high, bslice));
                seg_low = seg_high + 2;
                if seg_low > high {
                    break;
                }
            }
            //dbg!(segments[0].bslice.len(), segments.len());
            segments.iter_mut().for_each(|seg| seg.find(f, &sieve));
            sieve_seg.iter_mut().for_each(|x| *x = false);
            c += 1;
        }
        dbg!(c);
    }
}

#[derive(Debug)]
struct FILO<T>(Vec<T>);
impl<T: Copy + PartialEq> FILO<T> {
    fn new(value: T, size: usize) -> Self {
        FILO(vec![value; size])
    }
    #[inline(always)]
    fn push(&mut self, mut value: T) -> T {
        self.0.iter_mut().for_each(|v| { let tmp = *v; *v = value; value = tmp; } );
        self.0[self.0.len() - 1]
    }
    #[inline(always)]
    fn contains(&self, value: T) -> bool {
        self.0.iter().any(|x| *x == value)
    }
}

use time::PreciseTime;
use std::io::Write;
fn main() {
    let mut args = std::env::args()
        .skip(1)
        .map(|a| a
            .split('_')
            .fold("".to_string(), |a, s| a + s)
            .parse::<usize>());

    if args.len() <= 4 {
        if let (Ok(low), Ok(high), Ok(seg_size_kb), Ok(seg_num_chunks)) = (
                args.next().unwrap_or(Ok(3)),
                args.next().unwrap_or(Ok(1000000)),
                args.next().unwrap_or(Ok(32)),
                args.next().unwrap_or(Ok(4))) {
            let start = PreciseTime::now();
            if let Ok(primes) = Primes::new(low, high + 6, seg_size_kb, seg_num_chunks) {
                let mut count = 0;
                let mut nprimes = 0;
                let mut pbuf = FILO::new(0, 3);
                primes.callback(&mut |p| {//?? &mut? dyn?
                    if p <= high {
                        nprimes += 1;
                        if p < 200 { print!("{} ", p); }
                    }
                    if pbuf.contains(p) {
                        count += 1;
                    }
                    pbuf.push(p + 6);
                });
                let end = PreciseTime::now();
                println!("\ndone counting primes in {:.2} secs...", start.to(end).num_milliseconds() as f64 / 1000.0);
                println!("{} of {} primes are sexy", count, nprimes);
                return;
            }
        }
    }

    writeln!(
        std::io::stderr(),
        "Usage: sexy_primes low high seg_size(kb)"
    ).unwrap();
    std::process::exit(1);
}