1const MOD: u32 = 65521;
2const NMAX: usize = 5552;
3
4pub fn update(a: u16, b: u16, data: &[u8]) -> (u16, u16) {
5 let mut a = a as u32;
6 let mut b = b as u32;
7
8 let chunks = data.chunks_exact(NMAX);
9 let remainder = chunks.remainder();
10
11 for chunk in chunks {
12 for byte in chunk {
13 a = a.wrapping_add(*byte as _);
14 b = b.wrapping_add(a);
15 }
16
17 a %= MOD;
18 b %= MOD;
19 }
20
21 for byte in remainder {
22 a = a.wrapping_add(*byte as _);
23 b = b.wrapping_add(a);
24 }
25
26 a %= MOD;
27 b %= MOD;
28
29 (a as u16, b as u16)
30}
31
32#[cfg(test)]
33mod tests {
34 #[test]
35 fn zeroes() {
36 assert_eq!(adler32(&[]), 1);
37 assert_eq!(adler32(&[0]), 1 | 1 << 16);
38 assert_eq!(adler32(&[0, 0]), 1 | 2 << 16);
39 assert_eq!(adler32(&[0; 100]), 0x00640001);
40 assert_eq!(adler32(&[0; 1024]), 0x04000001);
41 assert_eq!(adler32(&[0; 1024 * 1024]), 0x00f00001);
42 }
43
44 #[test]
45 fn ones() {
46 assert_eq!(adler32(&[0xff; 1024]), 0x79a6fc2e);
47 assert_eq!(adler32(&[0xff; 1024 * 1024]), 0x8e88ef11);
48 }
49
50 #[test]
51 fn mixed() {
52 assert_eq!(adler32(&[1]), 2 | 2 << 16);
53 assert_eq!(adler32(&[40]), 41 | 41 << 16);
54
55 assert_eq!(adler32(&[0xA5; 1024 * 1024]), 0xd5009ab1);
56 }
57
58 /// Example calculation from https://en.wikipedia.org/wiki/Adler-32.
59 #[test]
60 fn wiki() {
61 assert_eq!(adler32(b"Wikipedia"), 0x11E60398);
62 }
63
64 fn adler32(data: &[u8]) -> u32 {
65 let (a, b) = super::update(1, 0, data);
66
67 u32::from(b) << 16 | u32::from(a)
68 }
69}
70