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comparison src/util/prng.rs @ 646:7d92730bf543

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Add a PRNG and use it for anm0 instruction 16.
author Emmanuel Gil Peyrot <linkmauve@linkmauve.fr>
date Sat, 03 Aug 2019 23:30:15 +0200
parents
children 1520b559cacc
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645:7bde50132735 646:7d92730bf543
1 //! Random number generator extracted from EoSD.
2
3 /// Pseudo-random number generator from EoSD.
4 #[derive(Debug)]
5 pub struct Prng {
6 seed: u16,
7 }
8
9 impl Prng {
10 /// Create a new pseudo-random number generator from this seed.
11 pub fn new(seed: u16) -> Prng {
12 Prng {
13 seed,
14 }
15 }
16
17 /// Generates a pseudo-random u16.
18 ///
19 /// RE’d from 102h.exe@0x41e780
20 pub fn get_u16(&mut self) -> u16 {
21 let x = ((self.seed ^ 0x9630) - 0x6553) & 0xffff;
22 self.seed = (((x & 0xc000) >> 14) | (x << 2)) & 0xffff;
23 self.seed
24 }
25
26 /// Combines two u16 into a single u32.
27 ///
28 /// RE’d from 102h.exe@0x41e7f0
29 pub fn get_u32(&mut self) -> u32 {
30 ((self.get_u16() as u32) << 16) | self.get_u16() as u32
31 }
32
33 /// Transforms an u32 into a f64.
34 ///
35 /// RE’d from 102h.exe@0x41e820
36 pub fn get_f64(&mut self) -> f64 {
37 self.get_u32() as f64 / (0x100000000u64 as f64)
38 }
39 }