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1 pub struct LaggedFibonacciPRNG { |
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2 circular_buffer: [u32; 64], |
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3 index: usize, |
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4 } |
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5 |
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6 impl LaggedFibonacciPRNG { |
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7 fn new(init_values: &[u8]) -> Self { |
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8 let mut buf = [0xa98765 + 68; 64]; |
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9 |
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10 for i in 0..std::cmp::min(init_values.len(), 54) { |
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11 buf[i] = init_values[i] as u32; |
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12 } |
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13 |
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14 let mut prng = Self { |
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15 circular_buffer: buf, |
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16 index: 54, |
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17 }; |
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18 |
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19 for i in 0..2048 { |
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20 prng.get_next(); |
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21 } |
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22 |
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23 prng |
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24 } |
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25 |
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26 #[inline] |
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27 fn get_next(&mut self) -> u32 { |
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28 self.index = (self.index + 1) & 0x3f; |
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29 self.circular_buffer[self.index] = (self.circular_buffer[(self.index + 40) & 0x3f] |
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30 + self.circular_buffer[(self.index + 9) & 0x3f]) |
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31 & 0x7fffffff; |
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32 |
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33 self.circular_buffer[self.index] |
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34 } |
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35 |
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36 #[inline] |
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37 fn get_random(&mut self, modulo: u32) -> u32 { |
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38 self.get_next(); |
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39 self.get_next() % modulo |
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40 } |
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41 |
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42 #[inline] |
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43 fn add_randomness(&mut self, value: u32) { |
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44 self.index = (self.index + 1) & 0x3f; |
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45 self.circular_buffer[self.index] ^= value; |
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46 } |
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47 } |
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48 |
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49 #[cfg(test)] |
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50 #[test] |
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51 fn compatibility() { |
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52 let mut prng = LaggedFibonacciPRNG::new("{052e2aee-ce41-4720-97bd-559a413bf866}".as_bytes()); |
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53 |
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54 assert_eq!(prng.get_random(1000), 418); |
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55 assert_eq!(prng.get_random(1000000), 554064); |
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56 assert_eq!(prng.get_random(0xffffffff), 239515837); |
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57 |
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58 prng.add_randomness(123); |
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59 |
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60 for i in 0..=100000 { |
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61 prng.get_random(2); |
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62 } |
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63 |
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64 assert_eq!(prng.get_random(0xffffffff), 525333582); |
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65 } |