idhash.rs

use std::hash::{Hasher, BuildHasherDefault};
use std::collections::HashMap;

pub type IdHasherBuilder = BuildHasherDefault<IdHasher>;
pub type IdHashMap<K, V> = HashMap<K, V, IdHasherBuilder>;
pub struct IdHasher(u64);

impl Default for IdHasher {
    #[inline]
    fn default() -> IdHasher {
        IdHasher(0)
    }
}

impl Hasher for IdHasher {
    #[inline]
    fn finish(&self) -> u64 {
        // Primes used in XXH64's finalizer.
        const PRIME_2: u64 = 14029467366897019727;
        const PRIME_3: u64 = 1609587929392839161;
        let mut hash = self.0;
        hash ^= hash >> 33;
        hash = hash.wrapping_mul(PRIME_2);
        hash ^= hash >> 29;
        hash = hash.wrapping_mul(PRIME_3);
        hash ^= hash >> 32;
        hash
    }

    #[inline]
    fn write(&mut self, bytes: &[u8]) {
        debug_assert!(bytes.len() <= 8);
        unsafe {
            let mut temp = 0u64;
            ::std::ptr::copy_nonoverlapping(bytes.as_ptr(),
                                            &mut temp as *mut _ as *mut u8,
                                            bytes.len());
            self.0 ^= temp;
        }
    }
}