refactor: random

uses a rust 1.83 feature so that the const fn works better

rust-toolchain.toml

@@ -0,0 +1,2 @@
+[toolchain]
+channel = "beta-2024-11-17"

src/hash.rs

@@ -13,22 +13,22 @@ Copyright © 2024 dogeystamp <dogeystamp@disroot.org>
 
 //! Zobrist hash implementation.
 
-use crate::random::{random_arr_2d_64, random_arr_64};
+use crate::random::Pcg64Random;
 use crate::{
     Board, CastleRights, ColPiece, Color, Square, BOARD_WIDTH, N_COLORS, N_PIECES, N_SQUARES,
 };
 
 const PIECE_KEYS: [[[u64; N_SQUARES]; N_PIECES]; N_COLORS] =
-    [random_arr_2d_64(11), random_arr_2d_64(22)];
+    [Pcg64Random::new(11).random_arr_2d_64(), Pcg64Random::new(22).random_arr_2d_64()];
 
 // 4 bits in castle perms -> 16 keys
-const CASTLE_KEYS: [u64; 16] = random_arr_64(33);
+const CASTLE_KEYS: [u64; 16] = Pcg64Random::new(33).random_arr_64();
 
 // ep can be specified by the file
-const EP_KEYS: [u64; BOARD_WIDTH] = random_arr_64(44);
+const EP_KEYS: [u64; BOARD_WIDTH] = Pcg64Random::new(44).random_arr_64();
 
 // current turn
-const COL_KEY: [u64; N_COLORS] = random_arr_64(55);
+const COL_KEY: [u64; N_COLORS] = Pcg64Random::new(55).random_arr_64();
 
 /// Zobrist hash state.
 ///

src/lib.rs

@@ -21,7 +21,7 @@ pub mod eval;
 pub mod fen;
 mod hash;
 pub mod movegen;
-mod random;
+pub mod random;
 pub mod search;
 
 use crate::fen::{FromFen, ToFen, START_POSITION};

src/random.rs

@@ -1,77 +1,82 @@
 //! Rust port by dogeystamp <dogeystamp@disroot.org> of
 //! the pcg64 dxsm random number generator (https://dotat.at/@/2023-06-21-pcg64-dxsm.html)
 
-struct Pcg64Random {
+pub struct Pcg64Random {
     state: u128,
     inc: u128,
 }
 
-/// Generates an array of random numbers.
-///
-/// The `rng` parameter only sets the initial state. This function is deterministic and pure.
-///
-/// # Returns
-///
-/// The array of random numbers, plus the RNG state at the end.
-const fn pcg64_dxsm<const N: usize>(mut rng: Pcg64Random) -> ([u64; N], Pcg64Random) {
-    let mut ret = [0; N];
-
-    const MUL: u64 = 15750249268501108917;
-
-    let mut i = 0;
-    while i < N {
-        let state: u128 = rng.state;
-        rng.state = state.wrapping_mul(MUL as u128).wrapping_add(rng.inc);
-        let mut hi: u64 = (state >> 64) as u64;
-        let lo: u64 = (state | 1) as u64;
-        hi ^= hi >> 32;
-        hi &= MUL;
-        hi ^= hi >> 48;
-        hi = hi.wrapping_mul(lo);
-        ret[i] = hi;
-
-        i += 1;
-    }
-
-    (ret, rng)
-}
-
 /// Make an RNG state "sane".
 const fn pcg64_seed(mut rng: Pcg64Random) -> Pcg64Random {
     // ensure rng.inc is odd
     rng.inc = (rng.inc << 1) | 1;
     rng.state += rng.inc;
     // one iteration of random
-    let (_, rng) = pcg64_dxsm::<1>(rng);
+    rng.rand();
     rng
 }
 
-/// Generate array of random numbers, based on a seed.
-///
-/// This function is pure and deterministic, and also works at compile-time rather than at runtime.
-///
-/// Example (generate 10 random numbers):
-///
-///```rust
-/// use crate::random::random_arr_64;
-/// const ARR: [u64; 10] = random_arr_64(123456);
-///```
-pub const fn random_arr_64<const N: usize>(seed: u128) -> [u64; N] {
-    let rng = pcg64_seed(Pcg64Random {
-        // chosen by fair dice roll
-        state: 24437033748623976104561743679864923857,
-        inc: seed,
-    });
-    pcg64_dxsm(rng).0
-}
-
-/// Generate 2D array of random numbers based on a seed.
-pub const fn random_arr_2d_64<const N: usize, const M: usize>(seed: u128) -> [[u64; N]; M] {
-    let mut ret = [[0; N]; M];
-    let mut i = 0;
-    while i < M {
-        ret[i] = random_arr_64(seed);
-        i += 1;
+impl Pcg64Random {
+    pub const fn new(seed: u128) -> Self {
+        pcg64_seed(Pcg64Random {
+            // chosen by fair dice roll
+            state: 24437033748623976104561743679864923857,
+            inc: seed,
+        })
+    }
+
+    /// Returns a single random number.
+    pub const fn rand(&mut self) -> u64 {
+        const MUL: u64 = 15750249268501108917;
+
+        let state: u128 = self.state;
+        self.state = state.wrapping_mul(MUL as u128).wrapping_add(self.inc);
+        let mut hi: u64 = (state >> 64) as u64;
+        let lo: u64 = (state | 1) as u64;
+        hi ^= hi >> 32;
+        hi &= MUL;
+        hi ^= hi >> 48;
+        hi = hi.wrapping_mul(lo);
+
+        hi
+    }
+
+    /// Generate array of random numbers, based on a seed.
+    ///
+    /// # Returns
+    ///
+    /// A tuple with the random number array, and the RNG state afterwards so you can reuse it in later
+    /// calls (otherwise you'll get the same result if you're using the same seed.)
+    ///
+    /// # Example
+    ///
+    ///```rust
+    /// use chess_inator::random::Pcg64Random;
+    ///
+    /// // generate 3 random numbers
+    /// const ARR: [u64; 3] = Pcg64Random::new(123456).random_arr_64();
+    /// assert_eq!(ARR, [4526545874411451611, 1124465636717751929, 12699417402402334336])
+    ///```
+    pub const fn random_arr_64<const N: usize>(&mut self) -> [u64; N] {
+        let mut ret = [0; N];
+        let mut i = 0;
+        while i < N {
+            let num = self.rand();
+            ret[i] = num;
+            i += 1;
+        }
+
+        ret
+    }
+
+    /// Generate 2D array of random numbers based on a seed.
+    pub const fn random_arr_2d_64<const N: usize, const M: usize>(&mut self) -> [[u64; N]; M] {
+        let mut ret = [[0; N]; M];
+        let mut i = 0;
+        while i < M {
+            ret[i] = self.random_arr_64();
+            i += 1;
+        }
+        ret
     }
-    ret
 }