/
hash.rs
62 lines (53 loc) · 1.51 KB
/
hash.rs
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// Ported from https://github.com/aappleby/smhasher/blob/61a0530f28277f2e850bfc39600ce61d02b518de/src/MurmurHash2.cpp#L37-L86
use byteorder::{ByteOrder, LittleEndian};
const M: u32 = 0x5bd1_e995;
pub(crate) fn murmurhash2(key: &[u8], initial_state: u32) -> u32 {
let mut h: u32 = initial_state;
let mut four_bytes_chunks = key.chunks_exact(4);
for chunk in four_bytes_chunks.by_ref() {
let mut k: u32 = LittleEndian::read_u32(chunk);
k = k.wrapping_mul(M);
k ^= k >> 24;
h = k.wrapping_mul(M) ^ h.wrapping_mul(M);
}
let remainder = four_bytes_chunks.remainder();
// Handle the last few bytes of the input array
match remainder.len() {
3 => {
h ^= u32::from(remainder[2]) << 16;
}
2 => {
h ^= u32::from(remainder[1]) << 8;
}
1 => {
h ^= u32::from(remainder[0]);
h = h.wrapping_mul(M);
}
_ => {}
}
h ^= h >> 13;
h = h.wrapping_mul(M);
h ^ (h >> 15)
}
#[cfg(test)]
mod test {
use super::murmurhash2;
#[test]
fn test_murmur2() {
let s1 = "abcdef";
let s2 = "abcdeg";
for i in 0..5 {
assert_eq!(
murmurhash2(s1[i..5].as_bytes(), 0),
murmurhash2(s2[i..5].as_bytes(), 0)
);
}
}
#[test]
fn verify_hash() {
assert_eq!(
murmurhash2("something".as_bytes(), 0),
u32::from_str_radix("crsxd7", 36).unwrap()
);
}
}