1 files changed, 74 insertions, 0 deletions
diff --git a/dungeon/src/rng.rs b/dungeon/src/rng.rs
new file mode 100644
index 0000000..bb9151b
--- /dev/null
+++ b/dungeon/src/rng.rs
@@ -0,0 +1,74 @@
+//! Implements rng using the xoshiro256++ algorithm
+
+use rand::{
+	SeedableRng,
+	rand_core::{RngCore, le},
+};
+
+/// Deterministic pseudo random number generator.
+///
+/// Is is a copy of `SmallRng` from `rand`, but is gurenteed
+/// to be reproducible across versions and platforms.
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub struct DungeonRng {
+	s: [u64; 4],
+}
+impl SeedableRng for DungeonRng {
+	// Fix to 256 bits. Changing this is a breaking change!
+	type Seed = [u8; 32];
+
+	#[inline]
+	fn from_seed(seed: Self::Seed) -> Self {
+		let mut state = [0; 4];
+		le::read_u64_into(&seed, &mut state);
+		Self { s: state }
+	}
+
+	#[inline]
+	fn seed_from_u64(mut state: u64) -> Self {
+		const PHI: u64 = 0x9e3779b97f4a7c15;
+		let mut s = [0; 4];
+		for i in &mut s {
+			state = state.wrapping_add(PHI);
+			let mut z = state;
+			z = (z ^ (z >> 30)).wrapping_mul(0xbf58476d1ce4e5b9);
+			z = (z ^ (z >> 27)).wrapping_mul(0x94d049bb133111eb);
+			z = z ^ (z >> 31);
+			*i = z;
+		}
+		Self { s }
+	}
+}
+impl RngCore for DungeonRng {
+	#[inline]
+	fn next_u32(&mut self) -> u32 {
+		let val = self.next_u64();
+		(val >> 32) as u32
+	}
+
+	#[inline]
+	fn next_u64(&mut self) -> u64 {
+		let res = self.s[0]
+			.wrapping_add(self.s[3])
+			.rotate_left(23)
+			.wrapping_add(self.s[0]);
+
+		let t = self.s[1] << 17;
+
+		self.s[2] ^= self.s[0];
+		self.s[3] ^= self.s[1];
+		self.s[1] ^= self.s[2];
+		self.s[0] ^= self.s[3];
+
+		self.s[2] ^= t;
+
+		self.s[3] = self.s[3].rotate_left(45);
+
+		res
+	}
+
+	#[inline]
+	fn fill_bytes(&mut self, dst: &mut [u8]) {
+		le::fill_bytes_via_next(self, dst);
+	}
+}