//! Shared TPDF dither PRNG for audio encoders.

/// Minimal xorshift64 PRNG for dither — no external dependency needed.
pub(crate) struct SimpleRng {
    state: u64,
}

impl SimpleRng {
    pub(crate) fn new(seed: u64) -> Self {
        // xorshift64 is degenerate with state 0 (outputs 0 forever)
        Self { state: if seed == 0 { 0x5A5A_5A5A_5A5A_5A5A } else { seed } }
    }

    fn next_u32(&mut self) -> u32 {
        // xorshift64
        self.state ^= self.state << 13;
        self.state ^= self.state >> 7;
        self.state ^= self.state << 17;
        (self.state & 0xFFFF_FFFF) as u32
    }

    pub(crate) fn next_f32(&mut self) -> f32 {
        self.next_u32() as f32 / u32::MAX as f32
    }
}