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Diffstat (limited to 'rand/rand_pcg/src/pcg64.rs')
-rw-r--r-- | rand/rand_pcg/src/pcg64.rs | 141 |
1 files changed, 0 insertions, 141 deletions
diff --git a/rand/rand_pcg/src/pcg64.rs b/rand/rand_pcg/src/pcg64.rs deleted file mode 100644 index 9177ec2..0000000 --- a/rand/rand_pcg/src/pcg64.rs +++ /dev/null @@ -1,141 +0,0 @@ -// 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)) - } -} |