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annotate utils/src/prng.rs @ 790:d005f5927447

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utils: Use const_for to make more const fn
author Link Mauve <linkmauve@linkmauve.fr>
date Sat, 17 Jan 2026 14:12:08 +0100
parents 1f152ca95658
children
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7d92730bf543 Add a PRNG and use it for anm0 instruction 16.
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1 //! Random number generator extracted from EoSD.
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2
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3 /// Pseudo-random number generator from EoSD.
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4 #[derive(Debug)]
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5 pub struct Prng {
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6 seed: u16,
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7 }
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8
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9 impl Prng {
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10 /// Create a new pseudo-random number generator from this seed.
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11 pub fn new(seed: Option<u16>) -> Prng {
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12 // TODO: Maybe add a getrandom::u16() to getrandom instead?
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13 let seed = seed.unwrap_or_else(|| getrandom::u32().unwrap() as u16);
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14 Prng {
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15 seed,
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16 }
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17 }
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18
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19 /// Generates a pseudo-random u16.
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20 ///
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21 /// RE’d from 102h.exe@0x41e780
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22 pub fn get_u16(&mut self) -> u16 {
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23 let x = (self.seed ^ 0x9630).wrapping_sub(0x6553);
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24 self.seed = ((x & 0xc000) >> 14) | (x << 2);
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25 self.seed
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26 }
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27
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28 /// Combines two u16 into a single u32.
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29 ///
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30 /// RE’d from 102h.exe@0x41e7f0
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31 pub fn get_u32(&mut self) -> u32 {
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32 ((self.get_u16() as u32) << 16) | self.get_u16() as u32
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33 }
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34
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35 /// Transforms an u32 into a f64.
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36 ///
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37 /// RE’d from 102h.exe@0x41e820
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38 pub fn get_f64(&mut self) -> f64 {
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39 self.get_u32() as f64 / (0x100000000u64 as f64)
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40 }
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41 }