sudachi/util/
fxhash.rs

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
/*
 *  Copyright (c) 2021 Works Applications Co., Ltd.
 *
 *  Licensed under the Apache License, Version 2.0 (the "License");
 *  you may not use this file except in compliance with the License.
 *  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 *   Unless required by applicable law or agreed to in writing, software
 *  distributed under the License is distributed on an "AS IS" BASIS,
 *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *  See the License for the specific language governing permissions and
 *  limitations under the License.
 */

// Adopted from: https://github.com/cbreeden/fxhash/blob/master/lib.rs
// Removed functionality that were useless for us
// Original Copyright:

// Copyright 2015 The Rust Project Developers. See the COPYRIGHT
// file at the top-level directory of this distribution and at
// http://rust-lang.org/COPYRIGHT.
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.

//! # Fx Hash
//!
//! This hashing algorithm was extracted from the Rustc compiler.  This is the same hashing
//! algorithm used for some internal operations in Firefox.  The strength of this algorithm
//! is in hashing 8 bytes at a time on 64-bit platforms, where the FNV algorithm works on one
//! byte at a time.
//!
//! ## Disclaimer
//!
//! It is **not a cryptographically secure** hash, so it is strongly recommended that you do
//! not use this hash for cryptographic purproses.  Furthermore, this hashing algorithm was
//! not designed to prevent any attacks for determining collisions which could be used to
//! potentially cause quadratic behavior in `HashMap`s.  So it is not recommended to expose
//! this hash in places where collissions or DDOS attacks may be a concern.

use std::convert::TryInto;
use std::default::Default;
use std::hash::{BuildHasherDefault, Hasher};
use std::ops::BitXor;

/// A builder for default Fx hashers.
pub type FxBuildHasher = BuildHasherDefault<FxHasher64>;

const ROTATE: u32 = 5;
const SEED64: u64 = 0x51_7c_c1_b7_27_22_0a_95;
const SEED32: u32 = 0x9e_37_79_b9;

#[cfg(target_pointer_width = "64")]
const SEED: usize = SEED64 as usize;

trait HashWord {
    fn hash_word(&mut self, _: Self);
}

macro_rules! impl_hash_word {
    ($($ty:ty = $key:ident),* $(,)*) => (
        $(
            impl HashWord for $ty {
                #[inline(always)]
                fn hash_word(&mut self, word: Self) {
                    *self = self.rotate_left(ROTATE).bitxor(word).wrapping_mul($key);
                }
            }
        )*
    )
}

impl_hash_word!(usize = SEED, u32 = SEED32, u64 = SEED64);

#[inline]
fn write64(mut hash: u64, mut bytes: &[u8]) -> u64 {
    while bytes.len() >= 8 {
        let (data, rem) = bytes.split_at(8);
        hash.hash_word(u64::from_ne_bytes(data.try_into().unwrap()));
        bytes = rem;
    }

    if bytes.len() >= 4 {
        let (data, rem) = bytes.split_at(4);
        hash.hash_word(u32::from_ne_bytes(data.try_into().unwrap()) as u64);
        bytes = rem;
    }

    if bytes.len() >= 2 {
        let (data, rem) = bytes.split_at(2);
        hash.hash_word(u16::from_ne_bytes(data.try_into().unwrap()) as u64);
        bytes = rem;
    }

    if let Some(&byte) = bytes.first() {
        hash.hash_word(u64::from(byte));
    }

    hash
}

/// This hashing algorithm was extracted from the Rustc compiler.
/// This is the same hashing algorithm used for some internal operations in Firefox.
/// The strength of this algorithm is in hashing 8 bytes at a time on any platform,
/// where the FNV algorithm works on one byte at a time.
///
/// This hashing algorithm should not be used for cryptographic, or in scenarios where
/// DOS attacks are a concern.
#[derive(Debug, Clone)]
pub struct FxHasher64 {
    hash: u64,
}

impl Default for FxHasher64 {
    #[inline]
    fn default() -> FxHasher64 {
        FxHasher64 { hash: 0 }
    }
}

impl Hasher for FxHasher64 {
    #[inline]
    fn finish(&self) -> u64 {
        self.hash
    }

    #[inline]
    fn write(&mut self, bytes: &[u8]) {
        self.hash = write64(self.hash, bytes);
    }

    #[inline]
    fn write_u8(&mut self, i: u8) {
        self.hash.hash_word(u64::from(i));
    }

    #[inline]
    fn write_u16(&mut self, i: u16) {
        self.hash.hash_word(u64::from(i));
    }

    #[inline]
    fn write_u32(&mut self, i: u32) {
        self.hash.hash_word(u64::from(i));
    }

    #[inline]
    fn write_u64(&mut self, i: u64) {
        self.hash.hash_word(i);
    }

    #[inline]
    fn write_usize(&mut self, i: usize) {
        self.hash.hash_word(i as u64);
    }
}