crc_thirty_too/
lib.rs

1// Copyright © 2026 Randy Barlow and Andrew Halle
2
3//! # crc-thirty-too
4//!
5//! TODO: Make a nice description.
6//!
7//! This is ported from [RFC 1952](https://www.rfc-editor.org/rfc/rfc1952.html#section-8).
8
9use std::sync::LazyLock;
10
11static FAST_CRC_TABLE: LazyLock<[u32; 256]> = LazyLock::new(|| {
12    let mut data = [0_u32; 256];
13
14    for (n, c) in data.iter_mut().enumerate() {
15        *c = n as u32;
16        for _ in 0..8 {
17            if *c % 2 == 0 {
18                *c >>= 1;
19            } else {
20                *c = 0xedb88320 ^ *c >> 1;
21            }
22        }
23    }
24
25    data
26});
27
28pub fn update_crc(crc: u32, bytes: &[u8]) -> u32 {
29    let mut c = crc ^ u32::MAX;
30
31    for byte in bytes {
32        let idx: usize = ((c as usize) ^ (*byte as usize)) & 0xFF;
33        c = (*FAST_CRC_TABLE)[idx] ^ (c >> 8);
34    }
35
36    c ^ u32::MAX
37}
38
39pub fn crc(bytes: &[u8]) -> u32 {
40    update_crc(0, bytes)
41}
42
43#[cfg(test)]
44mod tests {
45    use super::*;
46
47    #[test]
48    fn it_works() {
49        let input = b"hello world";
50
51        let actual = crc(input);
52
53        // hex(binascii.crc32(b'hello world'))
54        let expected = 0xd4a1185;
55
56        assert_eq!(actual, expected);
57    }
58}
crc_thirty_too/lib.rs

crc_thirty_too/
lib.rs
