39 lines
982 B
Rust
39 lines
982 B
Rust
//! Xorshift RNG used for tests. Based on the `rand_xorshift` crate.
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use core::num::Wrapping;
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/// Initial RNG state used in tests.
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// chosen by fair dice roll. guaranteed to be random.
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pub(crate) const RNG: XorShiftRng = XorShiftRng {
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x: Wrapping(0x0787_3B4A),
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y: Wrapping(0xFAAB_8FFE),
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z: Wrapping(0x1745_980F),
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w: Wrapping(0xB0AD_B4F3),
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};
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/// Xorshift RNG instance/
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pub(crate) struct XorShiftRng {
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x: Wrapping<u32>,
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y: Wrapping<u32>,
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z: Wrapping<u32>,
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w: Wrapping<u32>,
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}
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impl XorShiftRng {
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pub(crate) fn fill(&mut self, buf: &mut [u8; 1024]) {
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for chunk in buf.chunks_exact_mut(4) {
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chunk.copy_from_slice(&self.next_u32().to_le_bytes());
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}
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}
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fn next_u32(&mut self) -> u32 {
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let x = self.x;
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let t = x ^ (x << 11);
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self.x = self.y;
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self.y = self.z;
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self.z = self.w;
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let w = self.w;
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self.w = w ^ (w >> 19) ^ (t ^ (t >> 8));
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self.w.0
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}
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}
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