nanorand/rand/
pcg64.rs

1// Based off Robert Kern's C implementation at https://github.com/rkern/pcg64/blob/master/pcg64.c
2
3use crate::rand::{Rng, SeedableRng};
4use core::fmt::{self, Debug, Display, Formatter};
5#[cfg(feature = "zeroize")]
6use zeroize::Zeroize;
7
8const PCG_DEFAULT_MULTIPLIER_128: u128 = 47026247687942121848144207491837523525;
9
10/// An instance of the Pcg64 random number generator.
11/// Seeded from the system entropy generator when available.
12/// **This generator is _NOT_ cryptographically secure.**
13#[cfg_attr(feature = "zeroize", derive(Zeroize))]
14#[cfg_attr(feature = "zeroize", zeroize(drop))]
15pub struct Pcg64 {
16	seed: u128,
17	state: u128,
18	inc: u128,
19}
20
21impl Pcg64 {
22	/// Create a new [`Pcg64`] instance, seeding from the system's default source of entropy.
23	#[cfg(feature = "std")]
24	#[must_use]
25	pub fn new() -> Self {
26		let mut entropy: [u8; core::mem::size_of::<u128>()] = Default::default();
27		crate::entropy::system(&mut entropy);
28		Self {
29			seed: u128::from_ne_bytes(entropy),
30			inc: 0,
31			state: 0,
32		}
33	}
34
35	/// Create a new [`Pcg64`] instance, using a provided seed.
36	#[must_use]
37	pub const fn new_seed(seed: u128) -> Self {
38		Self {
39			seed,
40			inc: 0,
41			state: 0,
42		}
43	}
44
45	fn step(&mut self) {
46		self.state = self
47			.state
48			.wrapping_mul(PCG_DEFAULT_MULTIPLIER_128)
49			.wrapping_add(self.inc);
50	}
51
52	fn rand128(&mut self) -> u64 {
53		self.state = 0;
54		self.inc = self.seed.wrapping_shl(1) | 1;
55		self.step();
56		self.state = self.state.wrapping_add(self.seed);
57		self.step();
58		self.step();
59		self.state.wrapping_shr(64) as u64 ^ self.state as u64
60	}
61}
62
63#[cfg(feature = "std")]
64impl Default for Pcg64 {
65	/// Create a new [`Pcg64`] instance, seeding from the system's default source of entropy.
66	fn default() -> Self {
67		let mut entropy: [u8; core::mem::size_of::<u128>()] = Default::default();
68		crate::entropy::system(&mut entropy);
69		Self {
70			seed: u128::from_ne_bytes(entropy),
71			inc: 0,
72			state: 0,
73		}
74	}
75}
76
77impl Rng<8> for Pcg64 {
78	fn rand(&mut self) -> [u8; 8] {
79		let ret = self.rand128();
80		self.seed = self.state ^ (ret as u128).wrapping_shr(64);
81		ret.to_ne_bytes()
82	}
83}
84
85impl SeedableRng<16, 8> for Pcg64 {
86	fn reseed(&mut self, seed: [u8; 16]) {
87		self.seed = u128::from_ne_bytes(seed);
88	}
89}
90
91impl Clone for Pcg64 {
92	fn clone(&self) -> Self {
93		Self {
94			seed: self.seed,
95			inc: self.inc,
96			state: self.state,
97		}
98	}
99}
100
101impl Display for Pcg64 {
102	fn fmt(&self, f: &mut Formatter) -> fmt::Result {
103		write!(f, "Pcg64 ({:p})", self)
104	}
105}
106
107impl Debug for Pcg64 {
108	fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
109		f.debug_struct("Pcg64")
110			.field("seed", &format_args!("0x{:x}", self.seed))
111			.field("state", &format_args!("0x{:x}", self.state))
112			.field("inc", &format_args!("0x{:x}", self.inc))
113			.finish()
114	}
115}
nanorand/rand/pcg64.rs

nanorand/rand/
pcg64.rs
