foldhash/
quality.rs

1//! The foldhash implementation optimized for quality.
2
3use core::hash::{BuildHasher, Hasher};
4
5use crate::seed::SharedSeed;
6
7use crate::{fast, folded_multiply, ARBITRARY0, ARBITRARY8};
8
9/// A [`Hasher`] instance implementing foldhash, optimized for quality.
10///
11/// While you can create one directly with [`FoldHasher::with_seed`], you
12/// most likely want to use [`RandomState`], [`SeedableRandomState`] or
13/// [`FixedState`] to create [`FoldHasher`]s.
14#[derive(Clone)]
15pub struct FoldHasher {
16    pub(crate) inner: fast::FoldHasher,
17}
18
19impl FoldHasher {
20    /// Initializes this [`FoldHasher`] with the given per-hasher seed and
21    /// [`SharedSeed`].
22    #[inline(always)]
23    pub fn with_seed(per_hasher_seed: u64, shared_seed: &SharedSeed) -> FoldHasher {
24        FoldHasher {
25            inner: fast::FoldHasher::with_seed(per_hasher_seed, shared_seed),
26        }
27    }
28}
29
30impl Hasher for FoldHasher {
31    #[inline(always)]
32    fn write(&mut self, bytes: &[u8]) {
33        self.inner.write(bytes);
34    }
35
36    #[inline(always)]
37    fn write_u8(&mut self, i: u8) {
38        self.inner.write_u8(i);
39    }
40
41    #[inline(always)]
42    fn write_u16(&mut self, i: u16) {
43        self.inner.write_u16(i);
44    }
45
46    #[inline(always)]
47    fn write_u32(&mut self, i: u32) {
48        self.inner.write_u32(i);
49    }
50
51    #[inline(always)]
52    fn write_u64(&mut self, i: u64) {
53        self.inner.write_u64(i);
54    }
55
56    #[inline(always)]
57    fn write_u128(&mut self, i: u128) {
58        self.inner.write_u128(i);
59    }
60
61    #[inline(always)]
62    fn write_usize(&mut self, i: usize) {
63        self.inner.write_usize(i);
64    }
65
66    #[inline(always)]
67    fn finish(&self) -> u64 {
68        folded_multiply(self.inner.finish(), ARBITRARY0)
69    }
70}
71
72/// A [`BuildHasher`] for [`quality::FoldHasher`](FoldHasher) that is randomly initialized.
73#[derive(Copy, Clone, Default, Debug)]
74pub struct RandomState {
75    inner: fast::RandomState,
76}
77
78impl BuildHasher for RandomState {
79    type Hasher = FoldHasher;
80
81    #[inline(always)]
82    fn build_hasher(&self) -> FoldHasher {
83        FoldHasher {
84            inner: self.inner.build_hasher(),
85        }
86    }
87}
88
89/// A [`BuildHasher`] for [`quality::FoldHasher`](FoldHasher) that is randomly
90/// initialized by default, but can also be initialized with a specific seed.
91///
92/// This can be useful for e.g. testing, but the downside is that this type
93/// has a size of 16 bytes rather than the 8 bytes [`RandomState`] is.
94#[derive(Copy, Clone, Default, Debug)]
95pub struct SeedableRandomState {
96    inner: fast::SeedableRandomState,
97}
98
99impl SeedableRandomState {
100    /// Generates a random [`SeedableRandomState`], similar to [`RandomState`].
101    #[inline(always)]
102    pub fn random() -> Self {
103        Self {
104            inner: fast::SeedableRandomState::random(),
105        }
106    }
107
108    /// Generates a fixed [`SeedableRandomState`], similar to [`FixedState`].
109    #[inline(always)]
110    pub fn fixed() -> Self {
111        Self {
112            inner: fast::SeedableRandomState::fixed(),
113        }
114    }
115
116    /// Generates a [`SeedableRandomState`] with the given per-hasher seed
117    /// and [`SharedSeed`].
118    #[inline(always)]
119    pub fn with_seed(per_hasher_seed: u64, shared_seed: &'static SharedSeed) -> Self {
120        Self {
121            // We do an additional folded multiply with the seed here for
122            // the quality hash to ensure better independence between seed
123            // and hash.
124            inner: fast::SeedableRandomState::with_seed(
125                folded_multiply(per_hasher_seed, ARBITRARY8),
126                shared_seed,
127            ),
128        }
129    }
130}
131
132impl BuildHasher for SeedableRandomState {
133    type Hasher = FoldHasher;
134
135    #[inline(always)]
136    fn build_hasher(&self) -> FoldHasher {
137        FoldHasher {
138            inner: self.inner.build_hasher(),
139        }
140    }
141}
142
143/// A [`BuildHasher`] for [`quality::FoldHasher`](FoldHasher) that always has the same fixed seed.
144///
145/// Not recommended unless you absolutely need determinism.
146#[derive(Copy, Clone, Default, Debug)]
147pub struct FixedState {
148    inner: fast::FixedState,
149}
150
151impl FixedState {
152    /// Creates a [`FixedState`] with the given per-hasher seed.
153    #[inline(always)]
154    pub const fn with_seed(per_hasher_seed: u64) -> Self {
155        Self {
156            // We do an additional folded multiply with the seed here for
157            // the quality hash to ensure better independence between seed
158            // and hash. If the seed is zero the folded multiply is zero,
159            // preserving with_seed(0) == default().
160            inner: fast::FixedState::with_seed(folded_multiply(per_hasher_seed, ARBITRARY8)),
161        }
162    }
163}
164
165impl BuildHasher for FixedState {
166    type Hasher = FoldHasher;
167
168    #[inline(always)]
169    fn build_hasher(&self) -> FoldHasher {
170        FoldHasher {
171            inner: self.inner.build_hasher(),
172        }
173    }
174}
foldhash/quality.rs

foldhash/
quality.rs
