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annotate src/util/prng.rs @ 745:90e907859bae

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examples: Simplify PNG load functions.
author Emmanuel Gil Peyrot <linkmauve@linkmauve.fr>
date Sat, 18 Jan 2020 16:27:57 +0100
parents ac092b70c39a
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: u16) -> Prng {
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12 Prng {
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13 seed,
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14 }
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15 }
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16
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17 /// Generates a pseudo-random u16.
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18 ///
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19 /// RE’d from 102h.exe@0x41e780
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20 pub fn get_u16(&mut self) -> u16 {
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21 let x = (self.seed ^ 0x9630).wrapping_sub(0x6553);
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22 self.seed = ((x & 0xc000) >> 14) | (x << 2);
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23 self.seed
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24 }
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25
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26 /// Combines two u16 into a single u32.
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27 ///
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28 /// RE’d from 102h.exe@0x41e7f0
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29 pub fn get_u32(&mut self) -> u32 {
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30 ((self.get_u16() as u32) << 16) | self.get_u16() as u32
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31 }
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32
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33 /// Transforms an u32 into a f64.
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34 ///
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35 /// RE’d from 102h.exe@0x41e820
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36 pub fn get_f64(&mut self) -> f64 {
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37 self.get_u32() as f64 / (0x100000000u64 as f64)
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38 }
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39 }