77 lines
2.0 KiB
Rust
77 lines
2.0 KiB
Rust
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//! Rust port by dogeystamp <dogeystamp@disroot.org> of
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//! the pcg64 dxsm random number generator (https://dotat.at/@/2023-06-21-pcg64-dxsm.html)
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struct Pcg64Random {
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state: u128,
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inc: u128,
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}
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/// Generates an array of random numbers.
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///
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/// The `rng` parameter only sets the initial state. This function is deterministic and pure.
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///
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/// # Returns
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///
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/// The array of random numbers, plus the RNG state at the end.
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const fn pcg64_dxsm<const N: usize>(mut rng: Pcg64Random) -> ([u64; N], Pcg64Random) {
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let mut ret = [0; N];
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const MUL: u64 = 15750249268501108917;
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let mut i = 0;
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while i < N {
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let state: u128 = rng.state;
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rng.state = state.wrapping_mul(MUL as u128).wrapping_add(rng.inc);
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let mut hi: u64 = (state >> 64) as u64;
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let lo: u64 = (state | 1) as u64;
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hi ^= hi >> 32;
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hi &= MUL;
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hi ^= hi >> 48;
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hi = hi.wrapping_mul(lo);
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ret[i] = hi;
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i += 1;
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}
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(ret, rng)
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}
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/// Make an RNG state "sane".
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const fn pcg64_seed(mut rng: Pcg64Random) -> Pcg64Random {
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// ensure rng.inc is odd
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rng.inc = (rng.inc << 1) | 1;
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rng.state += rng.inc;
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// one iteration of random
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let (_, rng) = pcg64_dxsm::<1>(rng);
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rng
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}
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/// Generate array of random numbers, based on a seed.
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///
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/// This function is pure and deterministic, and also works at compile-time rather than at runtime.
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///
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/// Example (generate 10 random numbers):
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///
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///```rust
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/// const ARR: [u64; 10] = random_arr_64(123456);
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///```
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pub const fn random_arr_64<const N: usize>(seed: u128) -> [u64; N] {
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let rng = pcg64_seed(Pcg64Random {
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// chosen by fair dice roll
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state: 24437033748623976104561743679864923857,
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inc: seed,
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});
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pcg64_dxsm(rng).0
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}
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/// Generate 2D array of random numbers based on a seed.
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pub const fn random_arr_2d_64<const N: usize, const M: usize>(seed: u128) -> [[u64; N]; M] {
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let mut ret = [[0; N]; M];
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let mut i = 0;
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while i < M {
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ret[i] = random_arr_64(seed);
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i += 1;
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}
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ret
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}
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