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use core::num::Wrapping as w;
use core::{fmt, slice};
use {Rng, SeedableRng, Error};
use {impls, le};
#[derive(Clone)]
#[cfg_attr(feature="serde-1", derive(Serialize,Deserialize))]
pub struct XorShiftRng {
x: w<u32>,
y: w<u32>,
z: w<u32>,
w: w<u32>,
}
impl fmt::Debug for XorShiftRng {
fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
write!(f, "XorShiftRng {{}}")
}
}
impl XorShiftRng {
pub fn new_unseeded() -> XorShiftRng {
XorShiftRng {
x: w(0x193a6754),
y: w(0xa8a7d469),
z: w(0x97830e05),
w: w(0x113ba7bb),
}
}
}
impl Rng for XorShiftRng {
#[inline]
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
}
fn next_u64(&mut self) -> u64 {
impls::next_u64_via_u32(self)
}
fn fill_bytes(&mut self, dest: &mut [u8]) {
impls::fill_bytes_via_u32(self, dest)
}
}
impl SeedableRng for XorShiftRng {
type Seed = [u8; 16];
fn from_seed(seed: Self::Seed) -> Self {
let mut seed_u32 = [0u32; 4];
le::read_u32_into(&seed, &mut seed_u32);
if seed_u32.iter().all(|&x| x == 0) {
seed_u32 = [0xBAD_5EED, 0xBAD_5EED, 0xBAD_5EED, 0xBAD_5EED];
}
XorShiftRng {
x: w(seed_u32[0]),
y: w(seed_u32[1]),
z: w(seed_u32[2]),
w: w(seed_u32[3]),
}
}
fn from_rng<R: Rng>(mut rng: R) -> Result<Self, Error> {
let mut seed_u32 = [0u32; 4];
loop {
unsafe {
let ptr = seed_u32.as_mut_ptr() as *mut u8;
let slice = slice::from_raw_parts_mut(ptr, 4 * 4);
rng.try_fill_bytes(slice)?;
}
if !seed_u32.iter().all(|&x| x == 0) { break; }
}
Ok(XorShiftRng {
x: w(seed_u32[0]),
y: w(seed_u32[1]),
z: w(seed_u32[2]),
w: w(seed_u32[3]),
})
}
}
#[cfg(test)]
mod tests {
#[cfg(feature="serde-1")]
use {Rng, SeedableRng};
#[cfg(feature="serde-1")]
#[test]
fn test_serde() {
use super::XorShiftRng;
use thread_rng;
use bincode;
use std::io::{BufWriter, BufReader};
let seed: [u32; 4] = thread_rng().gen();
let mut rng: XorShiftRng = SeedableRng::from_seed(seed);
let buf: Vec<u8> = Vec::new();
let mut buf = BufWriter::new(buf);
bincode::serialize_into(&mut buf, &rng, bincode::Infinite).expect("Could not serialize");
let buf = buf.into_inner().unwrap();
let mut read = BufReader::new(&buf[..]);
let mut deserialized: XorShiftRng = bincode::deserialize_from(&mut read, bincode::Infinite).expect("Could not deserialize");
assert_eq!(rng.x, deserialized.x);
assert_eq!(rng.y, deserialized.y);
assert_eq!(rng.z, deserialized.z);
assert_eq!(rng.w, deserialized.w);
for _ in 0..16 {
assert_eq!(rng.next_u64(), deserialized.next_u64());
}
}
}