rust/src/libstd/hash.rs

// Copyright 2014 The Rust Project Developers. See the COPYRIGHT
// file at the top-level directory of this distribution and at
// http://rust-lang.org/COPYRIGHT.
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.

//! Generic hashing support.
//!
//! This module provides a generic way to compute the hash of a value. The
//! simplest way to make a type hashable is to use `#[deriving(Hash)]`:
//!
//! # Example
//!
//! ```rust
//! use std::hash;
//! use std::hash::Hash;
//!
//! #[deriving(Hash)]
//! struct Person {
//!     id: uint,
//!     name: String,
//!     phone: u64,
//! }
//!
//! let person1 = Person { id: 5, name: "Janet".to_string(), phone: 555_666_7777 };
//! let person2 = Person { id: 5, name: "Bob".to_string(), phone: 555_666_7777 };
//!
//! assert!(hash::hash(&person1) != hash::hash(&person2));
//! ```
//!
//! If you need more control over how a value is hashed, you need to implement
//! the trait `Hash`:
//!
//! ```rust
//! use std::hash;
//! use std::hash::Hash;
//! use std::hash::sip::SipState;
//!
//! struct Person {
//!     id: uint,
//!     name: String,
//!     phone: u64,
//! }
//!
//! impl Hash for Person {
//!     fn hash(&self, state: &mut SipState) {
//!         self.id.hash(state);
//!         self.phone.hash(state);
//!     }
//! }
//!
//! let person1 = Person { id: 5, name: "Janet".to_string(), phone: 555_666_7777 };
//! let person2 = Person { id: 5, name: "Bob".to_string(), phone: 555_666_7777 };
//!
//! assert!(hash::hash(&person1) == hash::hash(&person2));
//! ```

#![experimental]

pub use core_collections::hash::{Hash, Hasher, Writer, hash, sip};

use core::kinds::Sized;
use default::Default;
use rand::Rng;
use rand;

/// `RandomSipHasher` computes the SipHash algorithm from a stream of bytes
/// initialized with random keys.
#[deriving(Clone)]
pub struct RandomSipHasher {
    hasher: sip::SipHasher,
}

impl RandomSipHasher {
    /// Construct a new `RandomSipHasher` that is initialized with random keys.
    #[inline]
    pub fn new() -> RandomSipHasher {
        let mut r = rand::task_rng();
        let r0 = r.gen();
        let r1 = r.gen();
        RandomSipHasher {
            hasher: sip::SipHasher::new_with_keys(r0, r1),
        }
    }
}

impl Hasher<sip::SipState> for RandomSipHasher {
    #[inline]
    fn hash<Sized? T: Hash<sip::SipState>>(&self, value: &T) -> u64 {
        self.hasher.hash(value)
    }
}

impl Default for RandomSipHasher {
    #[inline]
    fn default() -> RandomSipHasher {
        RandomSipHasher::new()
    }
}