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#![allow(dead_code)]
use bit::{BitVec};
use std::{cmp};
use Primes;
#[derive(Debug)]
pub struct StreamingSieve {
small: Primes,
sieve: BitVec,
primes: Vec<(usize, usize)>,
low: usize,
current: usize,
limit: usize,
}
const CACHE: usize = 32 << 10;
const SEG_ELEMS: usize = 8 * CACHE;
const SEG_LEN: usize = 2 * SEG_ELEMS;
impl StreamingSieve {
pub fn new(limit: usize) -> StreamingSieve {
let small = Primes::sieve((limit as f64).sqrt() as usize + 1);
let current = 3;
let low = 0;
let elems = cmp::min(limit, SEG_ELEMS);
StreamingSieve {
small: small,
sieve: BitVec::from_elem(elems, false),
primes: vec![],
low: low,
current: current,
limit: limit
}
}
pub fn next(&mut self) -> Option<(usize, &BitVec)> {
if self.low >= self.limit {
return None
}
let low = self.low;
self.low += SEG_LEN;
let high = cmp::min(low + SEG_LEN - 1, self.limit);
self.sieve.clear();
let mut s = self.current;
while s * s <= high {
if self.small.is_prime(s) {
self.primes.push((s, s * s - low));
}
s += 1
}
self.current = s;
let top = cmp::min(SEG_LEN, self.limit) / 2;
for &mut (k, ref mut next) in self.primes.iter_mut() {
let mut j = *next / 2;
while j < top {
unsafe {
self.sieve.set_unchecked(j, true);
}
j += k;
}
*next = (2 * j + 1).wrapping_sub(SEG_LEN);
}
if low == 0 {
self.sieve.set(0, true);
}
Some((low, &self.sieve))
}
}
#[cfg(test)]
mod tests {
use super::StreamingSieve;
#[test]
fn test() {
const LIMIT: usize = 2_000_000;
let mut sieve = StreamingSieve::new(LIMIT);
let primes = ::Primes::sieve(LIMIT);
while let Some((low, next)) = sieve.next() {
let mut i = low + 1;
while i < low + next.len() {
if i > LIMIT { break }
assert!(primes.is_prime(i) == !next[(i - low) / 2],
"failed for {} (is prime = {})", i, primes.is_prime(i));
i += 2;
}
}
}
}
#[cfg(all(test, feature = "unstable"))]
mod benches {
use test::Bencher;
use bit::BitVec;
use super::StreamingSieve;
fn run(b: &mut Bencher, n: usize) {
b.iter(|| {
let mut sieve = StreamingSieve::new(n);
while sieve.next().is_some() {}
})
}
#[bench]
fn sieve_small(b: &mut Bencher) {
run(b, 100)
}
#[bench]
fn sieve_medium(b: &mut Bencher) {
run(b, 10_000)
}
#[bench]
fn sieve_large(b: &mut Bencher) {
run(b, 100_000)
}
#[bench]
fn sieve_larger(b: &mut Bencher) {
run(b, 1_000_000)
}
#[bench]
fn sieve_huge(b: &mut Bencher) {
run(b, 10_000_000)
}
}