squirrel_noise/
lib.rs

1/// Outputs a pseudo-random number between 0 and 1 based on the seed and the step
2///
3/// `step`: the step of the noise
4///
5/// `seed`: the seed of the noise (0 by default)
6///
7/// ref: <https://www.youtube.com/watch?v=LWFzPP8ZbdU>
8pub fn squirrel_noise(step: u32, seed: Option<u32>) -> f32 {
9    let bit_noise1: u32 = 0x68E31DA4;
10    let bit_noise2: u32 = 0xB5297A4D;
11    let bit_noise3: u32 = 0x1B56C4E9;
12
13    let mut mangled_bits: u32 = step;
14    mangled_bits = u32::wrapping_mul(mangled_bits, bit_noise1);
15    mangled_bits = u32::wrapping_add(mangled_bits, seed.unwrap_or(0));
16    mangled_bits ^= mangled_bits >> 8;
17    mangled_bits = u32::wrapping_add(mangled_bits, bit_noise2);
18    mangled_bits ^= mangled_bits << 8;
19    mangled_bits = u32::wrapping_mul(mangled_bits, bit_noise3);
20    mangled_bits ^= mangled_bits >> 8;
21
22    let max: u32 = 0xFFFFFFFF;
23    mangled_bits as f32 / max as f32
24}
25
26/// Creates a seeded random number generator with the given seed
27///
28/// `seed`: the seed of the noise
29pub fn seeded_squirrel_noise(seed: u32) -> impl Fn(u32) -> f32 {
30    move |step: u32| { squirrel_noise(step, Some(seed)) }
31}
32
33#[cfg(test)]
34mod tests {
35    use super::*;
36
37    #[test]
38    fn test_squirrel_noise() {
39        let length = 100;
40        for seed in 0..1000 {
41            let noise_sequence = (0..length).map(|step| squirrel_noise(step, Some(seed)));
42
43            let mean: f32 = noise_sequence.clone().sum::<f32>() / (length as f32);
44            assert!(mean > 0.4 && mean < 0.6);
45
46            for noise in noise_sequence {
47                assert!(noise >= 0.0);
48                assert!(noise <= 1.0);
49            }
50        }
51    }
52}