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use rand::RngCore;
use siphasher::sip::SipHasher13;
use std::hash::{Hash, Hasher};
#[derive(Clone, Copy, Debug)]
pub struct JumpHasher {
hs: SipHasher13,
}
impl Default for JumpHasher {
fn default() -> JumpHasher {
let mut rng = rand::thread_rng();
Self::new_with_keys(rng.next_u64(), rng.next_u64())
}
}
impl JumpHasher {
pub fn new() -> JumpHasher {
JumpHasher::default()
}
#[inline]
pub fn new_with_keys(k1: u64, k2: u64) -> JumpHasher {
JumpHasher {
hs: SipHasher13::new_with_keys(k1, k2),
}
}
pub fn slot<T: Hash>(&self, key: &T, slot_count: u32) -> u32 {
debug_assert!(slot_count > 0);
let mut hs = self.hs;
key.hash(&mut hs);
let mut h = hs.finish();
let (mut b, mut j) = (-1i64, 0i64);
while j < slot_count as i64 {
b = j;
h = h.wrapping_mul(2862933555777941757).wrapping_add(1);
j = ((b.wrapping_add(1) as f64) * (((1u64 << 31) as f64) / (((h >> 33) + 1) as f64)))
as i64;
}
b as u32
}
}
#[derive(Clone, Copy, Debug)]
pub struct CustomJumpHasher<H: Hasher + Clone> {
hs: H,
}
impl<H: Hasher + Clone> CustomJumpHasher<H> {
pub fn new(hasher: H) -> CustomJumpHasher<H> {
CustomJumpHasher { hs: hasher }
}
pub fn slot<T: Hash>(&self, key: &T, slot_count: u32) -> u32 {
debug_assert!(slot_count > 0);
let mut hs = self.hs.clone();
key.hash(&mut hs);
let mut h = hs.finish();
let (mut b, mut j) = (-1i64, 0i64);
while j < slot_count as i64 {
b = j;
h = h.wrapping_mul(2862933555777941757).wrapping_add(1);
j = ((b.wrapping_add(1) as f64) * (((1u64 << 31) as f64) / (((h >> 33) + 1) as f64)))
as i64;
}
b as u32
}
}
#[test]
fn test_basic() {
let j = JumpHasher::new_with_keys(0, 0);
assert_eq!(j.slot(&"test1", 10000000), 8970050);
assert_eq!(j.slot(&"test2", 1000), 10);
assert_eq!(j.slot(&"test3", 1000), 76);
assert_eq!(j.slot(&"test4", 1000), 161);
assert_eq!(j.slot(&"test5", 50), 33);
assert_eq!(j.slot(&"", 1000), 392);
assert_eq!(j.slot(&"testz", 1), 0);
let j = JumpHasher::new();
assert_ne!(j.slot(&"test1", 1000), 8970050);
let h0 = j.slot(&"test2", 1000);
assert_ne!(JumpHasher::new().slot(&"test2", 1000), h0);
}
#[test]
fn test_custom_hash() {
let j = CustomJumpHasher::new(SipHasher13::new_with_keys(0, 0));
assert_eq!(j.slot(&"test1", 10000000), 8970050);
assert_eq!(j.slot(&"test2", 1000), 10);
assert_eq!(j.slot(&"test3", 1000), 76);
assert_eq!(j.slot(&"test4", 1000), 161);
assert_eq!(j.slot(&"test5", 50), 33);
assert_eq!(j.slot(&"", 1000), 392);
assert_eq!(j.slot(&"testz", 1), 0);
let mut rng = rand::thread_rng();
let j = CustomJumpHasher::new(SipHasher13::new_with_keys(rng.next_u64(), rng.next_u64()));
assert_ne!(j.slot(&"test1", 1000), 8970050);
let h0 = j.slot(&"test2", 1000);
assert_ne!(
CustomJumpHasher::new(SipHasher13::new()).slot(&"test2", 1000),
h0
);
}