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annotate utils/src/prng.rs @ 792:11bc22bad1bf default tip

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python: Replace the image crate with png We weren’t using any of its features anyway, so the png crate is exactly what we need, without the many heavy dependencies of image. https://github.com/image-rs/image-png/pull/670 will eventually make it even faster to build.
author Link Mauve <linkmauve@linkmauve.fr>
date Sat, 17 Jan 2026 22:22:25 +0100
parents 1f152ca95658
children
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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 }