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//! Xorshift RNG used for tests. Based on the `rand_xorshift` crate.
use core::num::Wrapping;
/// Initial RNG state used in tests.
// chosen by fair dice roll. guaranteed to be random.
pub(crate) const RNG: XorShiftRng = XorShiftRng {
x: Wrapping(0x0787_3B4A),
y: Wrapping(0xFAAB_8FFE),
z: Wrapping(0x1745_980F),
w: Wrapping(0xB0AD_B4F3),
};
/// Xorshift RNG instance/
pub(crate) struct XorShiftRng {
x: Wrapping<u32>,
y: Wrapping<u32>,
z: Wrapping<u32>,
w: Wrapping<u32>,
}
impl XorShiftRng {
pub(crate) fn fill(&mut self, buf: &mut [u8; 1024]) {
for chunk in buf.chunks_exact_mut(4) {
chunk.copy_from_slice(&self.next_u32().to_le_bytes());
}
}
fn next_u32(&mut self) -> u32 {
let x = self.x;
let t = x ^ (x << 11);
self.x = self.y;
self.y = self.z;
self.z = self.w;
let w = self.w;
self.w = w ^ (w >> 19) ^ (t ^ (t >> 8));
self.w.0
}
}