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-// 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
-
-// This is the default multiplier used by PCG for 64-bit state.
-const MULTIPLIER: u128 = 0x2360_ED05_1FC6_5DA4_4385_DF64_9FCC_F645;
-
-use core::fmt;
-use core::mem::transmute;
-use rand_core::{RngCore, SeedableRng, Error, le};
-
-/// A PCG random number generator (XSL 128/64 (MCG) variant).
-///
-/// Permuted Congruential Generator with 128-bit state, internal Multiplicative
-/// Congruential Generator, and 64-bit output via "xorshift low (bits),
-/// random rotation" output function.
-///
-/// This is a 128-bit MCG with the PCG-XSL-RR output function.
-/// Note that compared to the standard `pcg64` (128-bit LCG with PCG-XSL-RR
-/// output function), this RNG is faster, also has a long cycle, and still has
-/// good performance on statistical tests.
-///
-/// Note: this RNG is only available using Rust 1.26 or later.
-#[derive(Clone)]
-#[cfg_attr(feature="serde1", derive(Serialize,Deserialize))]
-pub struct Mcg128Xsl64 {
- state: u128,
-}
-
-/// A friendly name for `Mcg128Xsl64`.
-pub type Pcg64Mcg = Mcg128Xsl64;
-
-impl Mcg128Xsl64 {
- /// Construct an instance compatible with PCG seed.
- ///
- /// Note that PCG specifies a default value for the parameter:
- ///
- /// - `state = 0xcafef00dd15ea5e5`
- pub fn new(state: u128) -> Self {
- // Force low bit to 1, as in C version (C++ uses `state | 3` instead).
- Mcg128Xsl64 { state: state | 1 }
- }
-}
-
-// Custom Debug implementation that does not expose the internal state
-impl fmt::Debug for Mcg128Xsl64 {
- fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
- write!(f, "Mcg128Xsl64 {{}}")
- }
-}
-
-/// We use a single 126-bit seed to initialise the state and select a stream.
-/// Two `seed` bits (lowest order of last byte) are ignored.
-impl SeedableRng for Mcg128Xsl64 {
- type Seed = [u8; 16];
-
- fn from_seed(seed: Self::Seed) -> Self {
- // Read as if a little-endian u128 value:
- let mut seed_u64 = [0u64; 2];
- le::read_u64_into(&seed, &mut seed_u64);
- let state = (seed_u64[0] as u128) |
- (seed_u64[1] as u128) << 64;
- Mcg128Xsl64::new(state)
- }
-}
-
-impl RngCore for Mcg128Xsl64 {
- #[inline]
- fn next_u32(&mut self) -> u32 {
- self.next_u64() as u32
- }
-
- #[inline]
- fn next_u64(&mut self) -> u64 {
- // prepare the LCG for the next round
- let state = self.state.wrapping_mul(MULTIPLIER);
- self.state = state;
-
- // Output function XSL RR ("xorshift low (bits), random rotation")
- // Constants are for 128-bit state, 64-bit output
- const XSHIFT: u32 = 64; // (128 - 64 + 64) / 2
- const ROTATE: u32 = 122; // 128 - 6
-
- let rot = (state >> ROTATE) as u32;
- let xsl = ((state >> XSHIFT) as u64) ^ (state as u64);
- xsl.rotate_right(rot)
- }
-
- #[inline]
- fn fill_bytes(&mut self, dest: &mut [u8]) {
- // specialisation of impls::fill_bytes_via_next; approx 3x faster
- let mut left = dest;
- while left.len() >= 8 {
- let (l, r) = {left}.split_at_mut(8);
- left = r;
- let chunk: [u8; 8] = unsafe {
- transmute(self.next_u64().to_le())
- };
- l.copy_from_slice(&chunk);
- }
- let n = left.len();
- if n > 0 {
- let chunk: [u8; 8] = unsafe {
- transmute(self.next_u64().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))
- }
-}