Main bitv example: prime sieve.

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Jonas Hietala 2014-07-20 14:45:33 +02:00 committed by Alex Crichton
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// option. This file may not be copied, modified, or distributed // option. This file may not be copied, modified, or distributed
// except according to those terms. // except according to those terms.
//! Collections implemented with bit vectors.
//!
//! # Example
//!
//! This is a simple example of the [Sieve of Eratosthenes][sieve]
//! which calculates prime numbers up to a given limit.
//!
//! [sieve]: http://en.wikipedia.org/wiki/Sieve_of_Eratosthenes
//!
//! ```
//! use std::collections::{BitvSet, Bitv};
//! use std::iter;
//!
//! let max_prime = 10000;
//!
//! // Store the primes as a BitvSet
//! let primes = {
//! let mut bv = Bitv::with_capacity(max_prime, true);
//!
//! // Neither 0 nor 1 are prime
//! bv.set(0, false);
//! bv.set(1, false);
//!
//! for i in range(2, max_prime) {
//! // if i is a prime
//! if bv.get(i) {
//! // mark all multiples of i as non-prime (any multiples below i * i
//! // will have been marked as non-prime previously)
//! for j in iter::range_step(i * i, max_prime, i) { bv.set(j, false) }
//! }
//! }
//! BitvSet::from_bitv(bv)
//! };
//!
//! // Simple primality tests below our max bound
//! let print_primes = 20;
//! print!("The primes below {} are: ", print_primes);
//! for x in range(0, print_primes) {
//! if primes.contains(&x) {
//! print!("{} ", x);
//! }
//! }
//! println!("");
//!
//! // We can manipulate the internal Bitv
//! let num_primes = primes.get_ref().iter().filter(|x| *x).count();
//! println!("There are {} primes below {}", num_primes, max_prime);
//! ```
#![allow(missing_doc)] #![allow(missing_doc)]
use core::prelude::*; use core::prelude::*;