use std::hash::{BuildHasher, Hasher};
const MULTIPLIER: u64 = 0x6eed0e9da4d94a4fu64;
const SEED: u64 = 0x16f11fe89b0d677cu64;
pub struct RoMu {}
impl RoMu {
pub fn new() -> RoMu {
RoMu {}
}
}
impl Default for RoMu {
fn default() -> Self {
RoMu::new()
}
}
impl BuildHasher for RoMu {
type Hasher = RoMuHash;
#[inline(always)]
fn build_hasher(&self) -> Self::Hasher {
RoMuHash::new()
}
}
pub struct RoMuHash {
state: u64,
}
impl RoMuHash {
#[inline(always)]
pub fn new() -> RoMuHash {
RoMuHash { state: SEED }
}
#[inline(always)]
fn consume(&mut self, value: u64) {
let data = self.state ^ value;
let data = data.wrapping_mul(MULTIPLIER);
self.state = data.rotate_left(32);
}
}
impl Hasher for RoMuHash {
#[inline(always)]
fn finish(&self) -> u64 {
self.state
}
#[inline(always)]
fn write(&mut self, _bytes: &[u8]) {
panic!("not supported for bytes")
}
#[inline(always)]
fn write_u8(&mut self, _: u8) {
panic!("not supported for u8")
}
#[inline(always)]
fn write_u16(&mut self, _: u16) {
panic!("not supported for u16")
}
#[inline(always)]
fn write_u32(&mut self, i: u32) {
self.consume(i as u64);
}
#[inline(always)]
fn write_u64(&mut self, i: u64) {
self.consume(i);
}
#[inline(always)]
fn write_u128(&mut self, _: u128) {
panic!("not supported for u128")
}
#[inline(always)]
fn write_usize(&mut self, i: usize) {
self.consume(i as u64);
}
#[inline(always)]
fn write_i8(&mut self, _: i8) {
panic!("not supported for i8")
}
#[inline(always)]
fn write_i16(&mut self, _: i16) {
panic!("not supported for i16")
}
#[inline(always)]
fn write_i32(&mut self, i: i32) {
self.consume(i as u64)
}
#[inline(always)]
fn write_i64(&mut self, i: i64) {
self.consume(i as u64)
}
#[inline(always)]
fn write_i128(&mut self, _: i128) {
panic!("not supported for i128")
}
#[inline(always)]
fn write_isize(&mut self, i: isize) {
self.consume(i as u64)
}
}
#[cfg(test)]
mod test {
use crate::hash::RoMu;
use std::collections::HashMap;
use std::hash::{Hash, Hasher};
#[derive(Eq, PartialEq)]
struct Small(i32, i32);
impl Hash for Small {
fn hash<H: Hasher>(&self, state: &mut H) {
state.write_u64((self.0 as u64) << 32 | (self.1 as u64))
}
}
#[test]
fn works_in_hashmap() {
let mut map = HashMap::with_hasher(RoMu::new());
map.insert(Small(5, 6), "data");
map.insert(Small(6, 5), "data2");
assert_eq!(*map.get(&Small(5, 6)).unwrap(), "data");
assert!(!map.contains_key(&Small(0, 0)));
}
}