use std::cell::Cell;
#[derive(Debug)]
pub(crate) struct FastRand {
one: Cell<u32>,
two: Cell<u32>,
}
impl FastRand {
pub(crate) fn new(seed: u64) -> FastRand {
let one = (seed >> 32) as u32;
let mut two = seed as u32;
if two == 0 {
two = 1;
}
FastRand {
one: Cell::new(one),
two: Cell::new(two),
}
}
pub(crate) fn fastrand_n(&self, n: u32) -> u32 {
let mul = (self.fastrand() as u64).wrapping_mul(n as u64);
(mul >> 32) as u32
}
fn fastrand(&self) -> u32 {
let mut s1 = self.one.get();
let s0 = self.two.get();
s1 ^= s1 << 17;
s1 = s1 ^ s0 ^ s1 >> 7 ^ s0 >> 16;
self.one.set(s0);
self.two.set(s1);
s0.wrapping_add(s1)
}
}
#[cfg(any(feature = "macros", feature = "stream"))]
#[doc(hidden)]
#[cfg_attr(not(feature = "macros"), allow(unreachable_pub))]
pub fn thread_rng_n(n: u32) -> u32 {
thread_local! {
static THREAD_RNG: FastRand = FastRand::new(crate::loom::rand::seed());
}
THREAD_RNG.with(|rng| rng.fastrand_n(n))
}