rand.rs

// borrowed from smoltcp
// https://github.com/smoltcp-rs/smoltcp/blob/774b375cb04e694199e27c7b9e36628436a4fac3/src/rand.rs

#[derive(Debug)]
#[cfg_attr(feature = "defmt", derive(defmt::Format))]
#[cfg_attr(feature = "ufmt", derive(ufmt::derive::uDebug))]
pub(crate) struct Rand {
    state: u64,
}

impl Rand {
    pub(crate) const fn new(seed: u64) -> Self {
        Self { state: seed }
    }

    pub(crate) fn next_u32(&mut self) -> u32 {
        // sPCG32 from https://www.pcg-random.org/paper.html
        // see also https://nullprogram.com/blog/2017/09/21/
        const M: u64 = 0xbb2efcec3c39611d;
        const A: u64 = 0x7590ef39;

        let s = self.state.wrapping_mul(M).wrapping_add(A);
        self.state = s;

        let shift = 29 - (s >> 61);
        (s >> shift) as u32
    }

    pub(crate) fn next_u16(&mut self) -> u16 {
        self.next_u32() as u16
    }
}