| // Copyright 2018 Developers of the Rand project. |
| // Copyright 2017 Paul Dicker. |
| // Copyright 2014-2017 Melissa O'Neill and PCG Project contributors |
| // |
| // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or |
| // https://www.apache.org/licenses/LICENSE-2.0> or the MIT license |
| // <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your |
| // option. This file may not be copied, modified, or distributed |
| // except according to those terms. |
| |
| //! PCG random number generators |
| |
| use core::fmt; |
| use core::mem::transmute; |
| use rand_core::{RngCore, SeedableRng, Error, le, impls}; |
| |
| // This is the default multiplier used by PCG for 64-bit state. |
| const MULTIPLIER: u64 = 6364136223846793005; |
| |
| /// A PCG random number generator (XSH RR 64/32 (LCG) variant). |
| /// |
| /// Permuted Congruential Generator with 64-bit state, internal Linear |
| /// Congruential Generator, and 32-bit output via "xorshift high (bits), |
| /// random rotation" output function. |
| /// |
| /// This is a 64-bit LCG with explicitly chosen stream with the PCG-XSH-RR |
| /// output function. This combination is the standard `pcg32`. |
| /// |
| /// Despite the name, this implementation uses 16 bytes (128 bit) space |
| /// comprising 64 bits of state and 64 bits stream selector. These are both set |
| /// by `SeedableRng`, using a 128-bit seed. |
| #[derive(Clone)] |
| #[cfg_attr(feature="serde1", derive(Serialize,Deserialize))] |
| pub struct Lcg64Xsh32 { |
| state: u64, |
| increment: u64, |
| } |
| |
| /// `Lcg64Xsh32` is also officially known as `pcg32`. |
| pub type Pcg32 = Lcg64Xsh32; |
| |
| impl Lcg64Xsh32 { |
| /// Construct an instance compatible with PCG seed and stream. |
| /// |
| /// Note that PCG specifies default values for both parameters: |
| /// |
| /// - `state = 0xcafef00dd15ea5e5` |
| /// - `stream = 721347520444481703` |
| pub fn new(state: u64, stream: u64) -> Self { |
| // The increment must be odd, hence we discard one bit: |
| let increment = (stream << 1) | 1; |
| Lcg64Xsh32::from_state_incr(state, increment) |
| } |
| |
| #[inline] |
| fn from_state_incr(state: u64, increment: u64) -> Self { |
| let mut pcg = Lcg64Xsh32 { state, increment }; |
| // Move away from inital value: |
| pcg.state = pcg.state.wrapping_add(pcg.increment); |
| pcg.step(); |
| pcg |
| } |
| |
| #[inline] |
| fn step(&mut self) { |
| // prepare the LCG for the next round |
| self.state = self.state |
| .wrapping_mul(MULTIPLIER) |
| .wrapping_add(self.increment); |
| } |
| } |
| |
| // Custom Debug implementation that does not expose the internal state |
| impl fmt::Debug for Lcg64Xsh32 { |
| fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result { |
| write!(f, "Lcg64Xsh32 {{}}") |
| } |
| } |
| |
| /// We use a single 127-bit seed to initialise the state and select a stream. |
| /// One `seed` bit (lowest bit of `seed[8]`) is ignored. |
| impl SeedableRng for Lcg64Xsh32 { |
| type Seed = [u8; 16]; |
| |
| fn from_seed(seed: Self::Seed) -> Self { |
| let mut seed_u64 = [0u64; 2]; |
| le::read_u64_into(&seed, &mut seed_u64); |
| |
| // The increment must be odd, hence we discard one bit: |
| Lcg64Xsh32::from_state_incr(seed_u64[0], seed_u64[1] | 1) |
| } |
| } |
| |
| impl RngCore for Lcg64Xsh32 { |
| #[inline] |
| fn next_u32(&mut self) -> u32 { |
| let state = self.state; |
| self.step(); |
| |
| // Output function XSH RR: xorshift high (bits), followed by a random rotate |
| // Constants are for 64-bit state, 32-bit output |
| const ROTATE: u32 = 59; // 64 - 5 |
| const XSHIFT: u32 = 18; // (5 + 32) / 2 |
| const SPARE: u32 = 27; // 64 - 32 - 5 |
| |
| let rot = (state >> ROTATE) as u32; |
| let xsh = (((state >> XSHIFT) ^ state) >> SPARE) as u32; |
| xsh.rotate_right(rot) |
| } |
| |
| #[inline] |
| fn next_u64(&mut self) -> u64 { |
| impls::next_u64_via_u32(self) |
| } |
| |
| #[inline] |
| fn fill_bytes(&mut self, dest: &mut [u8]) { |
| // specialisation of impls::fill_bytes_via_next; approx 40% faster |
| let mut left = dest; |
| while left.len() >= 4 { |
| let (l, r) = {left}.split_at_mut(4); |
| left = r; |
| let chunk: [u8; 4] = unsafe { |
| transmute(self.next_u32().to_le()) |
| }; |
| l.copy_from_slice(&chunk); |
| } |
| let n = left.len(); |
| if n > 0 { |
| let chunk: [u8; 4] = unsafe { |
| transmute(self.next_u32().to_le()) |
| }; |
| left.copy_from_slice(&chunk[..n]); |
| } |
| } |
| |
| #[inline] |
| fn try_fill_bytes(&mut self, dest: &mut [u8]) -> Result<(), Error> { |
| Ok(self.fill_bytes(dest)) |
| } |
| } |
| |
| #[cfg(test)] |
| mod tests { |
| use ::rand_core::{RngCore, SeedableRng}; |
| use super::*; |
| |
| #[test] |
| fn test_lcg64xsh32_construction() { |
| // Test that various construction techniques produce a working RNG. |
| let seed = [1,2,3,4, 5,6,7,8, 9,10,11,12, 13,14,15,16]; |
| let mut rng1 = Lcg64Xsh32::from_seed(seed); |
| assert_eq!(rng1.next_u64(), 1204678643940597513); |
| |
| let mut rng2 = Lcg64Xsh32::from_rng(&mut rng1).unwrap(); |
| assert_eq!(rng2.next_u64(), 12384929573776311845); |
| |
| let mut rng3 = Lcg64Xsh32::seed_from_u64(0); |
| assert_eq!(rng3.next_u64(), 18195738587432868099); |
| |
| // This is the same as Lcg64Xsh32, so we only have a single test: |
| let mut rng4 = Pcg32::seed_from_u64(0); |
| assert_eq!(rng4.next_u64(), 18195738587432868099); |
| } |
| |
| #[test] |
| fn test_lcg64xsh32_true_values() { |
| // Numbers copied from official test suite. |
| let mut rng = Lcg64Xsh32::new(42, 54); |
| |
| let mut results = [0u32; 6]; |
| for i in results.iter_mut() { *i = rng.next_u32(); } |
| let expected: [u32; 6] = [0xa15c02b7, 0x7b47f409, 0xba1d3330, |
| 0x83d2f293, 0xbfa4784b, 0xcbed606e]; |
| assert_eq!(results, expected); |
| } |
| |
| #[cfg(feature="serde1")] |
| #[test] |
| fn test_lcg64xsh32_serde() { |
| use bincode; |
| use std::io::{BufWriter, BufReader}; |
| |
| let mut rng = Lcg64Xsh32::seed_from_u64(0); |
| |
| let buf: Vec<u8> = Vec::new(); |
| let mut buf = BufWriter::new(buf); |
| bincode::serialize_into(&mut buf, &rng).expect("Could not serialize"); |
| |
| let buf = buf.into_inner().unwrap(); |
| let mut read = BufReader::new(&buf[..]); |
| let mut deserialized: Lcg64Xsh32 = bincode::deserialize_from(&mut read).expect("Could not deserialize"); |
| |
| assert_eq!(rng.state, deserialized.state); |
| |
| for _ in 0..16 { |
| assert_eq!(rng.next_u64(), deserialized.next_u64()); |
| } |
| } |
| } |