Steven Wroblewski
4df328243c
FNV-1a für Zustandsprüfsummen und SplitMix64 als einzige Zufallsquelle des Kerns. Beide sind gegen veröffentlichte Referenzwerte geprüft. Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>
35 lines
1.0 KiB
Rust
35 lines
1.0 KiB
Rust
//! Repeatable pseudo random numbers (SplitMix64).
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//!
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//! The core never uses any other source of randomness. The same seed always
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//! gives the same sequence, on every machine.
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/// Pseudo random number generator with 64 bits of state.
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#[derive(Clone, Debug, PartialEq, Eq)]
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pub struct Rng {
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state: u64,
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}
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impl Rng {
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pub fn new(seed: u64) -> Self {
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Self { state: seed }
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}
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/// Returns the next value of the sequence.
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pub fn next_u64(&mut self) -> u64 {
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self.state = self.state.wrapping_add(0x9E37_79B9_7F4A_7C15);
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let mut z = self.state;
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z = (z ^ (z >> 30)).wrapping_mul(0xBF58_476D_1CE4_E5B9);
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z = (z ^ (z >> 27)).wrapping_mul(0x94D0_49BB_1331_11EB);
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z ^ (z >> 31)
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}
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/// Returns a value in `0..bound`.
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///
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/// # Panics
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/// Panics if `bound` is zero.
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pub fn below(&mut self, bound: u32) -> u32 {
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assert!(bound > 0, "bound must be greater than zero");
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((u128::from(self.next_u64()) * u128::from(bound)) >> 64) as u32
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}
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}
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