devela/num/rand/xorshift/

u64.rs

// alazar::xorshift::u64
//
//! 64-bit version of XorShift.
//

#[cfg(feature = "join")]
use crate::Cast;
use crate::{xorshift_basis, ConstDefault, Own};

/// The `XorShift64` <abbr title="Pseudo-Random Number Generator">PRNG</abbr>.
///
/// It has a 64-bit state and generates 64-bit numbers.
///
/// This is the classic 64-bit *XorShift* by George Marsaglia.
///
/// The `BASIS` and triplet (`A`, `B`, `C`) values default to the canonical example.
#[must_use]
#[derive(Clone, Copy, Debug, PartialEq, Eq)]
pub struct XorShift64<
    const BASIS: usize = 0,
    const A: usize = 13,
    const B: usize = 7,
    const C: usize = 17,
>(u64);

/// Creates a new PRNG initialized with the default fixed seed.
impl Default for XorShift64 {
    fn default() -> Self {
        Self::DEFAULT
    }
}
/// Creates a new PRNG initialized with the default fixed seed.
impl ConstDefault for XorShift64 {
    const DEFAULT: Self = Self::new_unchecked(Self::DEFAULT_SEED);
}

// private associated items
impl<const BASIS: usize, const A: usize, const B: usize, const C: usize>
    XorShift64<BASIS, A, B, C>
{
    const DEFAULT_SEED: u64 = 0xDEFA_0017_DEFA_0017;

    #[cold] #[allow(dead_code)] #[rustfmt::skip]
    const fn cold_path_default() -> Self { Self::new_unchecked(Self::DEFAULT_SEED) }
}

impl<const BASIS: usize, const A: usize, const B: usize, const C: usize>
    XorShift64<BASIS, A, B, C>
{
    /// Returns a seeded `XorShift64` generator from the given 64-bit seed.
    ///
    /// If the seed is `0`, the default seed is used instead.
    pub const fn new(seed: u64) -> Self {
        if seed == 0 {
            Self::cold_path_default()
        } else {
            Self(seed)
        }
    }

    /// Returns a seeded `XorShift64` generator from the given 8-bit seed, unchecked.
    ///
    /// The seed must not be `0`, otherwise every result will also be `0`.
    pub const fn new_unchecked(seed: u64) -> Self {
        debug_assert![seed != 0, "Seed must be non-zero"];
        Self(seed)
    }

    #[must_use]
    /// Returns the PRNG's inner state as a raw snapshot.
    pub const fn inner_state(self) -> u64 {
        self.0
    }
    /// Restores the PRNG from the given state.
    pub const fn from_state(state: u64) -> Self {
        Self(state)
    }

    /// Returns the current random `u64`.
    #[must_use]
    pub const fn current_u64(&self) -> u64 {
        self.0
    }

    /// Returns the next random `u64`.
    #[must_use]
    pub fn next_u64(&mut self) -> u64 {
        let mut x = self.0;
        xorshift_basis!(x, BASIS, (A, B, C));
        self.0 = x;
        x
    }

    /// Returns a copy of the next new random state.
    pub const fn peek_next_state(&self) -> Self {
        let mut x = self.0;
        xorshift_basis!(x, BASIS, (A, B, C));
        Self(x)
    }

    /// Returns both the next random state and the `u64` value.
    pub const fn own_next_u64(self) -> Own<Self, u64> {
        let s = self.peek_next_state();
        let v = s.current_u64();
        Own::new(s, v)
    }
}

/// # Extra constructors
impl<const BASIS: usize, const A: usize, const B: usize, const C: usize>
    XorShift64<BASIS, A, B, C>
{
    /// Returns a seeded `XorShift64` generator from the given 64-bit seed.
    ///
    /// This is an alias of [`new`][Self#method.new].
    pub const fn new1_u64(seed: u64) -> Self {
        Self::new(seed)
    }

    /// Returns a seeded `XorShift64` generator from the given 2 × 32-bit seeds.
    ///
    /// The seeds will be joined in little endian order.
    #[cfg(feature = "join")]
    #[cfg_attr(feature = "nightly_doc", doc(cfg(feature = "join")))]
    pub const fn new2_u32(seeds: [u32; 2]) -> Self {
        Self::new(Cast::<u64>::from_u32_le(seeds))
    }

    /// Returns a seeded `XorShift64` generator from the given 4 × 16-bit seeds.
    ///
    /// The seeds will be joined in little endian order.
    #[cfg(feature = "join")]
    #[cfg_attr(feature = "nightly_doc", doc(cfg(feature = "join")))]
    pub const fn new4_u16(seeds: [u16; 4]) -> Self {
        Self::new(Cast::<u64>::from_u16_le(seeds))
    }

    /// Returns a seeded `XorShift64` generator from the given 4 × 8-bit seeds.
    ///
    /// The seeds will be joined in little endian order.
    pub const fn new8_u8(seeds: [u8; 8]) -> Self {
        Self::new(u64::from_le_bytes(seeds))
    }
}

#[cfg(feature = "dep_rand_core")]
#[cfg_attr(feature = "nightly_doc", doc(cfg(feature = "dep_rand_core")))]
mod impl_rand {
    use super::XorShift64;
    use crate::_dep::rand_core::{RngCore, SeedableRng};

    impl<const BASIS: usize, const A: usize, const B: usize, const C: usize> RngCore
        for XorShift64<BASIS, A, B, C>
    {
        /// Returns the next random `u32`,
        /// from the first 32-bits of `next_u64`.
        fn next_u32(&mut self) -> u32 {
            self.next_u64() as u32
        }

        /// Returns the next random `u64`.
        fn next_u64(&mut self) -> u64 {
            self.next_u64()
        }

        fn fill_bytes(&mut self, dest: &mut [u8]) {
            let mut i = 0;
            while i < dest.len() {
                let random_u64 = self.next_u64();
                let bytes = random_u64.to_le_bytes();
                let remaining = dest.len() - i;

                if remaining >= 8 {
                    dest[i..i + 8].copy_from_slice(&bytes);
                    i += 8;
                } else {
                    dest[i..].copy_from_slice(&bytes[..remaining]);
                    break;
                }
            }
        }
    }

    impl<const BASIS: usize, const A: usize, const B: usize, const C: usize> SeedableRng
        for XorShift64<BASIS, A, B, C>
    {
        type Seed = [u8; 8];

        /// When seeded with zero this implementation uses the default seed
        /// value as the cold path.
        fn from_seed(seed: Self::Seed) -> Self {
            if seed == [0; 8] {
                Self::cold_path_default()
            } else {
                Self::new_unchecked(u64::from_le_bytes(seed))
            }
        }
    }
}

/// 275 × good triplets for 64-bit xorshift. (825 Bytes)
#[doc(hidden)]
#[rustfmt::skip]
#[allow(dead_code)]
pub const XOROSHIFT_64_TRIPLETS: [(u8, u8, u8); 275] = [
    ( 1, 1,54), ( 1, 1,55), ( 1, 3,45), ( 1, 7, 9), ( 1, 7,44), ( 1, 7,46),
    ( 1, 9,50), ( 1,11,35), ( 1,11,50), ( 1,13,45), ( 1,15, 4), ( 1,15,63),
    ( 1,19, 6), ( 1,19,16), ( 1,23,14), ( 1,23,29), ( 1,29,34), ( 1,35, 5),
    ( 1,35,11), ( 1,35,34), ( 1,45,37), ( 1,51,13), ( 1,53, 3), ( 1,59,14),
    ( 2,13,23), ( 2,31,51), ( 2,31,53), ( 2,43,27), ( 2,47,49), ( 3, 1,11),
    ( 3, 5,21), ( 3,13,59), ( 3,21,31), ( 3,25,20), ( 3,25,31), ( 3,25,56),
    ( 3,29,40), ( 3,29,47), ( 3,29,49), ( 3,35,14), ( 3,37,17), ( 3,43, 4),
    ( 3,43, 6), ( 3,43,11), ( 3,51,16), ( 3,53, 7), ( 3,61,17), ( 3,61,26),
    ( 4, 7,19), ( 4, 9,13), ( 4,15,51), ( 4,15,53), ( 4,29,45), ( 4,29,49),
    ( 4,31,33), ( 4,35,15), ( 4,35,21), ( 4,37,11), ( 4,37,21), ( 4,41,19),
    ( 4,41,45), ( 4,43,21), ( 4,43,31), ( 4,53, 7), ( 5, 9,23), ( 5,11,54),
    ( 5,15,27), ( 5,17,11), ( 5,23,36), ( 5,33,29), ( 5,41,20), ( 5,45,16),
    ( 5,47,23), ( 5,53,20), ( 5,59,33), ( 5,59,35), ( 5,59,63), ( 6, 1,17),
    ( 6, 3,49), ( 6,17,47), ( 6,23,27), ( 6,27, 7), ( 6,43,21), ( 6,49,29),
    ( 6,55,17), ( 7, 5,41), ( 7, 5,47), ( 7, 5,55), ( 7, 7,20), ( 7, 9,38),
    ( 7,11,10), ( 7,11,35), ( 7,13,58), ( 7,19,17), ( 7,19,54), ( 7,23, 8),
    ( 7,25,58), ( 7,27,59), ( 7,33, 8), ( 7,41,40), ( 7,43,28), ( 7,51,24),
    ( 7,57,12), ( 8, 5,59), ( 8, 9,25), ( 8,13,25), ( 8,13,61), ( 8,15,21),
    ( 8,25,59), ( 8,29,19), ( 8,31,17), ( 8,37,21), ( 8,51,21), ( 9, 1,27),
    ( 9, 5,36), ( 9, 5,43), ( 9, 7,18), ( 9,19,18), ( 9,21,11), ( 9,21,20),
    ( 9,21,40), ( 9,23,57), ( 9,27,10), ( 9,29,12), ( 9,29,37), ( 9,37,31),
    ( 9,41,45), (10, 7,33), (10,27,59), (10,53,13), (11, 5,32), (11, 5,34),
    (11, 5,43), (11, 5,45), (11, 9,14), (11, 9,34), (11,13,40), (11,15,37),
    (11,23,42), (11,23,56), (11,25,48), (11,27,26), (11,29,14), (11,31,18),
    (11,53,23), (12, 1,31), (12, 3,13), (12, 3,49), (12, 7,13), (12,11,47),
    (12,25,27), (12,39,49), (12,43,19), (13, 3,40), (13, 3,53), (13, 7,17),
    (13, 9,15), (13, 9,50), (13,13,19), (13,17,43), (13,19,28), (13,19,47),
    (13,21,18), (13,21,49), (13,29,35), (13,35,30), (13,35,38), (13,47,23),
    (13,51,21), (14,13,17), (14,15,19), (14,23,33), (14,31,45), (14,47,15),
    (15, 1,19), (15, 5,37), (15,13,28), (15,13,52), (15,17,27), (15,19,63),
    (15,21,46), (15,23,23), (15,45,17), (15,47,16), (15,49,26), (16, 5,17),
    (16, 7,39), (16,11,19), (16,11,27), (16,13,55), (16,21,35), (16,25,43),
    (16,27,53), (16,47,17), (17,15,58), (17,23,29), (17,23,51), (17,23,52),
    (17,27,22), (17,45,22), (17,47,28), (17,47,29), (17,47,54), (18, 1,25),
    (18, 3,43), (18,19,19), (18,25,21), (18,41,23), (19, 7,36), (19, 7,55),
    (19,13,37), (19,15,46), (19,21,52), (19,25,20), (19,41,21), (19,43,27),
    (20, 1,31), (20, 5,29), (21, 1,27), (21, 9,29), (21,13,52), (21,15,28),
    (21,15,29), (21,17,24), (21,17,30), (21,17,48), (21,21,32), (21,21,34),
    (21,21,37), (21,21,38), (21,21,40), (21,21,41), (21,21,43), (21,41,23),
    (22, 3,39), (23, 9,38), (23, 9,48), (23, 9,57), (23,13,38), (23,13,58),
    (23,13,61), (23,17,25), (23,17,54), (23,17,56), (23,17,62), (23,41,34),
    (23,41,51), (24, 9,35), (24,11,29), (24,25,25), (24,31,35), (25, 7,46),
    (25, 7,49), (25, 9,39), (25,11,57), (25,13,29), (25,13,39), (25,13,62),
    (25,15,47), (25,21,44), (25,27,27), (25,27,53), (25,33,36), (25,39,54),
    (28, 9,55), (28,11,53), (29,27,37), (31, 1,51), (31,25,37), (31,27,35),
    (33,31,43), (33,31,55), (43,21,46), (49,15,61), (55, 9,56)
];