122 lines
3.1 KiB
Rust
122 lines
3.1 KiB
Rust
// Copyright (C) 2022 Lucas Schwiderski
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//
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// This program is free software: you can redistribute it and/or modify
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// it under the terms of the GNU General Public License as published by
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// the Free Software Foundation, either version 3 of the License, or
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// (at your option) any later version.
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//
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// This program is distributed in the hope that it will be useful,
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// but WITHOUT ANY WARRANTY; without even the implied warranty of
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// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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// GNU General Public License for more details.
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//
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// You should have received a copy of the GNU General Public License
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// along with this program. If not, see <https://www.gnu.org/licenses/>.
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//
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// Adapted from https://github.com/badboy/murmurhash64-rs
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// 'M' and 'R' are mixing constants generated offline.
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// They're not really 'magic', they just happen to work well.
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const M: u64 = 0xc6a4a7935bd1e995;
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// Multiplicative inverse of `M` under % 2^64
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const M_INVERSE: u64 = 0x5f7a0ea7e59b19bd;
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const R: u8 = 47;
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pub fn hash(key: &[u8], seed: u64) -> u64 {
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let len = key.len();
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let mut h: u64 = seed ^ ((len as u64).wrapping_mul(M));
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let endpos = len - (len & 7);
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let mut i = 0;
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while i != endpos {
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let mut k: u64;
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k = key[i] as u64;
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k |= (key[i + 1] as u64) << 8;
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k |= (key[i + 2] as u64) << 16;
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k |= (key[i + 3] as u64) << 24;
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k |= (key[i + 4] as u64) << 32;
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k |= (key[i + 5] as u64) << 40;
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k |= (key[i + 6] as u64) << 48;
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k |= (key[i + 7] as u64) << 56;
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k = k.wrapping_mul(M);
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k ^= k >> R;
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k = k.wrapping_mul(M);
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h ^= k;
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h = h.wrapping_mul(M);
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i += 8;
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}
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let overflow = len & 7;
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if overflow == 7 {
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h ^= (key[i + 6] as u64) << 48;
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}
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if overflow >= 6 {
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h ^= (key[i + 5] as u64) << 40;
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}
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if overflow >= 5 {
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h ^= (key[i + 4] as u64) << 32;
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}
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if overflow >= 4 {
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h ^= (key[i + 3] as u64) << 24;
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}
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if overflow >= 3 {
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h ^= (key[i + 2] as u64) << 16;
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}
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if overflow >= 2 {
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h ^= (key[i + 1] as u64) << 8;
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}
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if overflow >= 1 {
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h ^= key[i] as u64;
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}
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if overflow > 0 {
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h = h.wrapping_mul(M);
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}
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h ^= h >> R;
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h = h.wrapping_mul(M);
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h ^= h >> R;
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h
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}
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pub fn hash_inverse(hash: u64, seed: u64) -> u64 {
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let mut h = hash;
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h ^= h >> R;
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h = h.wrapping_mul(M_INVERSE);
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h ^= h >> R;
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h = h.wrapping_mul(M_INVERSE);
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let h_forward: u64 = seed ^ (M.wrapping_mul(8));
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let mut k: u64 = h ^ h_forward;
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k = k.wrapping_mul(M_INVERSE);
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k ^= k >> R;
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k = k.wrapping_mul(M_INVERSE);
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// let mut k = k.to_ne_bytes();
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// k.reverse();
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// u64::from_ne_bytes(k)
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k
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}
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pub fn hash32(key: &[u8], seed: u32) -> u32 {
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let h = hash(key, seed as u64);
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(h >> 32) as u32
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}
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#[test]
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fn test_hash() {
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assert_eq!(0, hash("".as_bytes(), 0));
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assert_eq!(0xc26e8bc196329b0f, hash("".as_bytes(), 10));
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assert_eq!(0xa14e8dfa2cd117e2, hash("lua".as_bytes(), 0));
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assert_eq!(
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0x069A33456AAD3042,
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hash("twitch_intervention".as_bytes(), 0)
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);
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}
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#[test]
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fn test_inverse() {}
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