aboutsummaryrefslogtreecommitdiff
path: root/rand/rand_pcg/src
diff options
context:
space:
mode:
Diffstat (limited to 'rand/rand_pcg/src')
-rw-r--r--rand/rand_pcg/src/lib.rs21
-rw-r--r--rand/rand_pcg/src/pcg128.rs177
-rw-r--r--rand/rand_pcg/src/pcg64.rs26
3 files changed, 157 insertions, 67 deletions
diff --git a/rand/rand_pcg/src/lib.rs b/rand/rand_pcg/src/lib.rs
index 9648e85..22ba4a0 100644
--- a/rand/rand_pcg/src/lib.rs
+++ b/rand/rand_pcg/src/lib.rs
@@ -17,11 +17,12 @@
//! - `Pcg32` aka `Lcg64Xsh32`, officially known as `pcg32`, a general
//! purpose RNG. This is a good choice on both 32-bit and 64-bit CPUs
//! (for 32-bit output).
-//! - `Pcg64Mcg` aka `Mcg128Xsl64`, officially known as `mcg_xsl_rr_128_64`,
+//! - `Pcg64` aka `Lcg128Xsl64`, officially known as `pcg64`, a general
+//! purpose RNG. This is a good choice on 64-bit CPUs.
+//! - `Pcg64Mcg` aka `Mcg128Xsl64`, officially known as `pcg64_fast`,
//! a general purpose RNG using 128-bit multiplications. This has poor
//! performance on 32-bit CPUs but is a good choice on 64-bit CPUs for
-//! both 32-bit and 64-bit output. (Note: this RNG is only available using
-//! Rust 1.26 or later.)
+//! both 32-bit and 64-bit output.
//!
//! Both of these use 16 bytes of state and 128-bit seeds, and are considered
//! value-stable (i.e. any change affecting the output given a fixed seed would
@@ -34,15 +35,15 @@
#![deny(missing_docs)]
#![deny(missing_debug_implementations)]
-#![no_std]
-
-pub extern crate rand_core;
+#![allow(clippy::unreadable_literal)]
-#[cfg(feature="serde1")] extern crate serde;
-#[cfg(feature="serde1")] #[macro_use] extern crate serde_derive;
+#![no_std]
mod pcg64;
-#[cfg(all(rustc_1_26, not(target_os = "emscripten")))] mod pcg128;
+#[cfg(not(target_os = "emscripten"))] mod pcg128;
pub use self::pcg64::{Pcg32, Lcg64Xsh32};
-#[cfg(all(rustc_1_26, not(target_os = "emscripten")))] pub use self::pcg128::{Pcg64Mcg, Mcg128Xsl64};
+#[cfg(not(target_os = "emscripten"))] pub use self::pcg128::{
+ Pcg64, Lcg128Xsl64,
+ Pcg64Mcg, Mcg128Xsl64,
+};
diff --git a/rand/rand_pcg/src/pcg128.rs b/rand/rand_pcg/src/pcg128.rs
index 9aff506..311a41b 100644
--- a/rand/rand_pcg/src/pcg128.rs
+++ b/rand/rand_pcg/src/pcg128.rs
@@ -14,8 +14,109 @@
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};
+#[cfg(feature="serde1")] use serde::{Serialize, Deserialize};
+
+/// A PCG random number generator (XSL RR 128/64 (LCG) variant).
+///
+/// Permuted Congruential Generator with 128-bit state, internal Linear
+/// Congruential Generator, and 64-bit output via "xorshift low (bits),
+/// random rotation" output function.
+///
+/// This is a 128-bit LCG with explicitly chosen stream with the PCG-XSL-RR
+/// output function. This combination is the standard `pcg64`.
+///
+/// Despite the name, this implementation uses 32 bytes (256 bit) space
+/// comprising 128 bits of state and 128 bits stream selector. These are both
+/// set by `SeedableRng`, using a 256-bit seed.
+#[derive(Clone)]
+#[cfg_attr(feature="serde1", derive(Serialize,Deserialize))]
+pub struct Lcg128Xsl64 {
+ state: u128,
+ increment: u128,
+}
+
+/// `Lcg128Xsl64` is also officially known as `pcg64`.
+pub type Pcg64 = Lcg128Xsl64;
+
+impl Lcg128Xsl64 {
+ /// Construct an instance compatible with PCG seed and stream.
+ ///
+ /// Note that PCG specifies default values for both parameters:
+ ///
+ /// - `state = 0xcafef00dd15ea5e5`
+ /// - `stream = 0xa02bdbf7bb3c0a7ac28fa16a64abf96`
+ pub fn new(state: u128, stream: u128) -> Self {
+ // The increment must be odd, hence we discard one bit:
+ let increment = (stream << 1) | 1;
+ Lcg128Xsl64::from_state_incr(state, increment)
+ }
+
+ #[inline]
+ fn from_state_incr(state: u128, increment: u128) -> Self {
+ let mut pcg = Lcg128Xsl64 { 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 Lcg128Xsl64 {
+ fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+ write!(f, "Lcg128Xsl64 {{}}")
+ }
+}
+
+/// We use a single 255-bit seed to initialise the state and select a stream.
+/// One `seed` bit (lowest bit of `seed[8]`) is ignored.
+impl SeedableRng for Lcg128Xsl64 {
+ type Seed = [u8; 32];
+
+ fn from_seed(seed: Self::Seed) -> Self {
+ let mut seed_u64 = [0u64; 4];
+ le::read_u64_into(&seed, &mut seed_u64);
+ let state = u128::from(seed_u64[0]) | (u128::from(seed_u64[1]) << 64);
+ let incr = u128::from(seed_u64[2]) | (u128::from(seed_u64[3]) << 64);
+
+ // The increment must be odd, hence we discard one bit:
+ Lcg128Xsl64::from_state_incr(state, incr | 1)
+ }
+}
+
+impl RngCore for Lcg128Xsl64 {
+ #[inline]
+ fn next_u32(&mut self) -> u32 {
+ self.next_u64() as u32
+ }
+
+ #[inline]
+ fn next_u64(&mut self) -> u64 {
+ self.step();
+ output_xsl_rr(self.state)
+ }
+
+ #[inline]
+ fn fill_bytes(&mut self, dest: &mut [u8]) {
+ fill_bytes_impl(self, dest)
+ }
+
+ #[inline]
+ fn try_fill_bytes(&mut self, dest: &mut [u8]) -> Result<(), Error> {
+ self.fill_bytes(dest);
+ Ok(())
+ }
+}
+
/// A PCG random number generator (XSL 128/64 (MCG) variant).
///
@@ -23,19 +124,18 @@ use rand_core::{RngCore, SeedableRng, Error, le};
/// 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.
+/// This is a 128-bit MCG with the PCG-XSL-RR output function, also known as
+/// `pcg64_fast`.
/// 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`.
+/// A friendly name for `Mcg128Xsl64` (also known as `pcg64_fast`).
pub type Pcg64Mcg = Mcg128Xsl64;
impl Mcg128Xsl64 {
@@ -66,8 +166,8 @@ impl SeedableRng for Mcg128Xsl64 {
// 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;
+ let state = u128::from(seed_u64[0]) |
+ u128::from(seed_u64[1]) << 64;
Mcg128Xsl64::new(state)
}
}
@@ -80,43 +180,46 @@ impl RngCore for Mcg128Xsl64 {
#[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)
+ self.state = self.state.wrapping_mul(MULTIPLIER);
+ output_xsl_rr(self.state)
}
#[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]);
- }
+ fill_bytes_impl(self, dest)
}
#[inline]
fn try_fill_bytes(&mut self, dest: &mut [u8]) -> Result<(), Error> {
- Ok(self.fill_bytes(dest))
+ self.fill_bytes(dest);
+ Ok(())
+ }
+}
+
+#[inline(always)]
+fn output_xsl_rr(state: u128) -> u64 {
+ // 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(always)]
+fn fill_bytes_impl<R: RngCore + ?Sized>(rng: &mut R, dest: &mut [u8]) {
+ let mut left = dest;
+ while left.len() >= 8 {
+ let (l, r) = {left}.split_at_mut(8);
+ left = r;
+ let chunk: [u8; 8] = rng.next_u64().to_le_bytes();
+ l.copy_from_slice(&chunk);
+ }
+ let n = left.len();
+ if n > 0 {
+ let chunk: [u8; 8] = rng.next_u64().to_le_bytes();
+ left.copy_from_slice(&chunk[..n]);
}
}
diff --git a/rand/rand_pcg/src/pcg64.rs b/rand/rand_pcg/src/pcg64.rs
index 9177ec2..fadc6dc 100644
--- a/rand/rand_pcg/src/pcg64.rs
+++ b/rand/rand_pcg/src/pcg64.rs
@@ -11,8 +11,8 @@
//! PCG random number generators
use core::fmt;
-use core::mem::transmute;
use rand_core::{RngCore, SeedableRng, Error, le, impls};
+#[cfg(feature="serde1")] use serde::{Serialize, Deserialize};
// This is the default multiplier used by PCG for 64-bit state.
const MULTIPLIER: u64 = 6364136223846793005;
@@ -45,7 +45,8 @@ impl Lcg64Xsh32 {
/// Note that PCG specifies default values for both parameters:
///
/// - `state = 0xcafef00dd15ea5e5`
- /// - `stream = 721347520444481703`
+ /// - `stream = 0xa02bdbf7bb3c0a7`
+ // Note: stream is 1442695040888963407u64 >> 1
pub fn new(state: u64, stream: u64) -> Self {
// The increment must be odd, hence we discard one bit:
let increment = (stream << 1) | 1;
@@ -115,27 +116,12 @@ impl RngCore for Lcg64Xsh32 {
#[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]);
- }
+ impls::fill_bytes_via_next(self, dest)
}
#[inline]
fn try_fill_bytes(&mut self, dest: &mut [u8]) -> Result<(), Error> {
- Ok(self.fill_bytes(dest))
+ self.fill_bytes(dest);
+ Ok(())
}
}
generated by cgit v1.2.3 (git 2.46.0) at 2025-10-31 14:07:23 +0000