/* This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

//! This file stolen wholesale from rustc/src/librustc/util/nodemap.rs

pub use std::hash::{Hash, Hasher, Writer};

/// A speedy hash algorithm for node ids and def ids. The hashmap in
/// libcollections by default uses SipHash which isn't quite as speedy as we
/// want. In the compiler we're not really worried about DOS attempts, so we
/// just default to a non-cryptographic hash.
///
/// This uses FNV hashing, as described here:
/// http://en.wikipedia.org/wiki/Fowler%E2%80%93Noll%E2%80%93Vo_hash_function
#[deriving(Clone)]
pub struct FnvHasher;

pub struct FnvState(u64);

impl Hasher<FnvState> for FnvHasher {
    fn hash<Sized? T: Hash<FnvState>>(&self, t: &T) -> u64 {
        let mut state = FnvState(0xcbf29ce484222325);
        t.hash(&mut state);
        let FnvState(ret) = state;
        return ret;
    }
}

impl Writer for FnvState {
    fn write(&mut self, bytes: &[u8]) {
        let FnvState(mut hash) = *self;
        for byte in bytes.iter() {
            hash = hash ^ (*byte as u64);
            hash = hash * 0x100000001b3;
        }
        *self = FnvState(hash);
    }
}

#[inline(always)]
pub fn hash<T: Hash<FnvState>>(t: &T) -> u64 {
    let s = FnvHasher;
    s.hash(t)
}