xxhash_rust/
const_xxh32.rs

1//!Const eval friendly xxh32 implementation.
2
3use core::mem;
4
5use crate::xxh32_common::*;
6
7#[inline(always)]
8const fn read_u32(input: &[u8], cursor: usize) -> u32 {
9    input[cursor] as u32 | (input[cursor + 1] as u32) << 8 | (input[cursor + 2] as u32) << 16 | (input[cursor + 3] as u32) << 24
10}
11
12const fn finalize(mut input: u32, data: &[u8], mut cursor: usize) -> u32 {
13    let mut len = data.len() - cursor;
14
15    while len >= 4 {
16        input = input.wrapping_add(
17            read_u32(data, cursor).wrapping_mul(PRIME_3)
18        );
19        cursor += mem::size_of::<u32>();
20        len -= mem::size_of::<u32>();
21        input = input.rotate_left(17).wrapping_mul(PRIME_4);
22    }
23
24    while len > 0 {
25        input = input.wrapping_add((data[cursor] as u32).wrapping_mul(PRIME_5));
26        cursor += mem::size_of::<u8>();
27        len -= mem::size_of::<u8>();
28        input = input.rotate_left(11).wrapping_mul(PRIME_1);
29    }
30
31    avalanche(input)
32}
33
34///Const variant of xxh32 hashing
35pub const fn xxh32(input: &[u8], seed: u32) -> u32 {
36    let mut result = input.len() as u32;
37    let mut cursor = 0;
38
39    if input.len() >= CHUNK_SIZE {
40        let mut v1 = seed.wrapping_add(PRIME_1).wrapping_add(PRIME_2);
41        let mut v2 = seed.wrapping_add(PRIME_2);
42        let mut v3 = seed;
43        let mut v4 = seed.wrapping_sub(PRIME_1);
44
45        loop {
46            v1 = round(v1, read_u32(input, cursor));
47            cursor += mem::size_of::<u32>();
48            v2 = round(v2, read_u32(input, cursor));
49            cursor += mem::size_of::<u32>();
50            v3 = round(v3, read_u32(input, cursor));
51            cursor += mem::size_of::<u32>();
52            v4 = round(v4, read_u32(input, cursor));
53            cursor += mem::size_of::<u32>();
54
55            if (input.len() - cursor) < CHUNK_SIZE {
56                break;
57            }
58        }
59
60        result = result.wrapping_add(
61            v1.rotate_left(1).wrapping_add(
62                v2.rotate_left(7).wrapping_add(
63                    v3.rotate_left(12).wrapping_add(
64                        v4.rotate_left(18)
65                    )
66                )
67            )
68        );
69    } else {
70        result = result.wrapping_add(seed.wrapping_add(PRIME_5));
71    }
72
73    finalize(result, input, cursor)
74}
xxhash_rust/const_xxh32.rs

xxhash_rust/
const_xxh32.rs
