1#[cfg(feature = "default-hasher")]
2use {
3 core::hash::{BuildHasher, Hasher},
4 foldhash::fast::RandomState,
5};
6
7/// Default hash builder for the `S` type parameter of
8/// [`HashMap`](crate::HashMap) and [`HashSet`](crate::HashSet).
9///
10/// This only implements `BuildHasher` when the "default-hasher" crate feature
11/// is enabled; otherwise it just serves as a placeholder, and a custom `S` type
12/// must be used to have a fully functional `HashMap` or `HashSet`.
13#[derive(Clone, Debug, Default)]
14pub struct DefaultHashBuilder {
15 #[cfg(feature = "default-hasher")]
16 inner: RandomState,
17}
18
19#[cfg(feature = "default-hasher")]
20impl BuildHasher for DefaultHashBuilder {
21 type Hasher = DefaultHasher;
22
23 #[inline(always)]
24 fn build_hasher(&self) -> Self::Hasher {
25 DefaultHasher {
26 inner: self.inner.build_hasher(),
27 }
28 }
29}
30
31/// Default hasher for [`HashMap`](crate::HashMap) and [`HashSet`](crate::HashSet).
32#[cfg(feature = "default-hasher")]
33#[derive(Clone)]
34pub struct DefaultHasher {
35 inner: <RandomState as BuildHasher>::Hasher,
36}
37
38#[cfg(feature = "default-hasher")]
39macro_rules! forward_writes {
40 ($( $write:ident ( $ty:ty ) , )*) => {$(
41 #[inline(always)]
42 fn $write(&mut self, arg: $ty) {
43 self.inner.$write(arg);
44 }
45 )*}
46}
47
48#[cfg(feature = "default-hasher")]
49impl Hasher for DefaultHasher {
50 forward_writes! {
51 write(&[u8]),
52 write_u8(u8),
53 write_u16(u16),
54 write_u32(u32),
55 write_u64(u64),
56 write_u128(u128),
57 write_usize(usize),
58 write_i8(i8),
59 write_i16(i16),
60 write_i32(i32),
61 write_i64(i64),
62 write_i128(i128),
63 write_isize(isize),
64 }
65
66 // feature(hasher_prefixfree_extras)
67 #[cfg(feature = "nightly")]
68 forward_writes! {
69 write_length_prefix(usize),
70 write_str(&str),
71 }
72
73 #[inline(always)]
74 fn finish(&self) -> u64 {
75 self.inner.finish()
76 }
77}
78