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Diffstat (limited to 'rand/rand_pcg/src/pcg128.rs')
-rw-r--r-- | rand/rand_pcg/src/pcg128.rs | 122 |
1 files changed, 0 insertions, 122 deletions
diff --git a/rand/rand_pcg/src/pcg128.rs b/rand/rand_pcg/src/pcg128.rs deleted file mode 100644 index 9aff506..0000000 --- a/rand/rand_pcg/src/pcg128.rs +++ /dev/null @@ -1,122 +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 - -// 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)) - } -} |