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1 | // Copyright 2013 The Rust Project Developers. See the COPYRIGHT |
2 | // file at the top-level directory of this distribution and at | |
3 | // http://rust-lang.org/COPYRIGHT. | |
4 | // | |
5 | // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or | |
6 | // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license | |
7 | // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your | |
8 | // option. This file may not be copied, modified, or distributed | |
9 | // except according to those terms. | |
10 | ||
11 | //! A wrapper around another RNG that reseeds it after it | |
12 | //! generates a certain number of random bytes. | |
13 | ||
14 | use core::prelude::*; | |
15 | ||
16 | use {Rng, SeedableRng}; | |
17 | use core::default::Default; | |
18 | ||
19 | /// How many bytes of entropy the underling RNG is allowed to generate | |
20 | /// before it is reseeded. | |
21 | static DEFAULT_GENERATION_THRESHOLD: uint = 32 * 1024; | |
22 | ||
23 | /// A wrapper around any RNG which reseeds the underlying RNG after it | |
24 | /// has generated a certain number of random bytes. | |
25 | pub struct ReseedingRng<R, Rsdr> { | |
26 | rng: R, | |
27 | generation_threshold: uint, | |
28 | bytes_generated: uint, | |
29 | /// Controls the behaviour when reseeding the RNG. | |
30 | pub reseeder: Rsdr, | |
31 | } | |
32 | ||
33 | impl<R: Rng, Rsdr: Reseeder<R>> ReseedingRng<R, Rsdr> { | |
34 | /// Create a new `ReseedingRng` with the given parameters. | |
35 | /// | |
36 | /// # Arguments | |
37 | /// | |
38 | /// * `rng`: the random number generator to use. | |
39 | /// * `generation_threshold`: the number of bytes of entropy at which to reseed the RNG. | |
40 | /// * `reseeder`: the reseeding object to use. | |
41 | pub fn new(rng: R, generation_threshold: uint, reseeder: Rsdr) -> ReseedingRng<R,Rsdr> { | |
42 | ReseedingRng { | |
43 | rng: rng, | |
44 | generation_threshold: generation_threshold, | |
45 | bytes_generated: 0, | |
46 | reseeder: reseeder | |
47 | } | |
48 | } | |
49 | ||
50 | /// Reseed the internal RNG if the number of bytes that have been | |
51 | /// generated exceed the threshold. | |
52 | pub fn reseed_if_necessary(&mut self) { | |
53 | if self.bytes_generated >= self.generation_threshold { | |
54 | self.reseeder.reseed(&mut self.rng); | |
55 | self.bytes_generated = 0; | |
56 | } | |
57 | } | |
58 | } | |
59 | ||
60 | ||
61 | impl<R: Rng, Rsdr: Reseeder<R>> Rng for ReseedingRng<R, Rsdr> { | |
62 | fn next_u32(&mut self) -> u32 { | |
63 | self.reseed_if_necessary(); | |
64 | self.bytes_generated += 4; | |
65 | self.rng.next_u32() | |
66 | } | |
67 | ||
68 | fn next_u64(&mut self) -> u64 { | |
69 | self.reseed_if_necessary(); | |
70 | self.bytes_generated += 8; | |
71 | self.rng.next_u64() | |
72 | } | |
73 | ||
74 | fn fill_bytes(&mut self, dest: &mut [u8]) { | |
75 | self.reseed_if_necessary(); | |
76 | self.bytes_generated += dest.len(); | |
77 | self.rng.fill_bytes(dest) | |
78 | } | |
79 | } | |
80 | ||
81 | impl<S, R: SeedableRng<S>, Rsdr: Reseeder<R> + Default> | |
82 | SeedableRng<(Rsdr, S)> for ReseedingRng<R, Rsdr> { | |
83 | fn reseed(&mut self, (rsdr, seed): (Rsdr, S)) { | |
84 | self.rng.reseed(seed); | |
85 | self.reseeder = rsdr; | |
86 | self.bytes_generated = 0; | |
87 | } | |
88 | ||
89 | /// Create a new `ReseedingRng` from the given reseeder and | |
90 | /// seed. This uses a default value for `generation_threshold`. | |
91 | fn from_seed((rsdr, seed): (Rsdr, S)) -> ReseedingRng<R, Rsdr> { | |
92 | ReseedingRng { | |
93 | rng: SeedableRng::from_seed(seed), | |
94 | generation_threshold: DEFAULT_GENERATION_THRESHOLD, | |
95 | bytes_generated: 0, | |
96 | reseeder: rsdr | |
97 | } | |
98 | } | |
99 | } | |
100 | ||
101 | /// Something that can be used to reseed an RNG via `ReseedingRng`. | |
102 | /// | |
103 | /// # Example | |
104 | /// | |
105 | /// ```rust | |
106 | /// use std::rand::{Rng, SeedableRng, StdRng}; | |
107 | /// use std::rand::reseeding::{Reseeder, ReseedingRng}; | |
108 | /// | |
109 | /// struct TickTockReseeder { tick: bool } | |
110 | /// impl Reseeder<StdRng> for TickTockReseeder { | |
111 | /// fn reseed(&mut self, rng: &mut StdRng) { | |
112 | /// let val = if self.tick {0} else {1}; | |
113 | /// rng.reseed(&[val]); | |
114 | /// self.tick = !self.tick; | |
115 | /// } | |
116 | /// } | |
117 | /// fn main() { | |
118 | /// let rsdr = TickTockReseeder { tick: true }; | |
119 | /// | |
120 | /// let inner = StdRng::new().unwrap(); | |
121 | /// let mut rng = ReseedingRng::new(inner, 10, rsdr); | |
122 | /// | |
123 | /// // this will repeat, because it gets reseeded very regularly. | |
124 | /// let s: String = rng.gen_ascii_chars().take(100).collect(); | |
125 | /// println!("{}", s); | |
126 | /// } | |
127 | /// | |
128 | /// ``` | |
129 | pub trait Reseeder<R> { | |
130 | /// Reseed the given RNG. | |
131 | fn reseed(&mut self, rng: &mut R); | |
132 | } | |
133 | ||
134 | /// Reseed an RNG using a `Default` instance. This reseeds by | |
135 | /// replacing the RNG with the result of a `Default::default` call. | |
136 | #[derive(Copy)] | |
85aaf69f SL |
137 | pub struct ReseedWithDefault { __hack: [u8; 0] } |
138 | // FIXME(#21721) used to be an unit struct but that can cause | |
139 | // certain LLVM versions to abort during optimizations. | |
140 | #[allow(non_upper_case_globals)] | |
141 | pub const ReseedWithDefault: ReseedWithDefault = ReseedWithDefault { __hack: [] }; | |
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142 | |
143 | impl<R: Rng + Default> Reseeder<R> for ReseedWithDefault { | |
144 | fn reseed(&mut self, rng: &mut R) { | |
145 | *rng = Default::default(); | |
146 | } | |
147 | } | |
85aaf69f | 148 | #[stable(feature = "rust1", since = "1.0.0")] |
1a4d82fc | 149 | impl Default for ReseedWithDefault { |
85aaf69f | 150 | #[stable(feature = "rust1", since = "1.0.0")] |
1a4d82fc JJ |
151 | fn default() -> ReseedWithDefault { ReseedWithDefault } |
152 | } | |
153 | ||
154 | #[cfg(test)] | |
155 | mod test { | |
156 | use std::prelude::v1::*; | |
157 | ||
158 | use core::iter::{order, repeat}; | |
159 | use super::{ReseedingRng, ReseedWithDefault}; | |
160 | use std::default::Default; | |
161 | use {SeedableRng, Rng}; | |
162 | ||
163 | struct Counter { | |
164 | i: u32 | |
165 | } | |
166 | ||
167 | impl Rng for Counter { | |
168 | fn next_u32(&mut self) -> u32 { | |
169 | self.i += 1; | |
170 | // very random | |
171 | self.i - 1 | |
172 | } | |
173 | } | |
174 | impl Default for Counter { | |
175 | fn default() -> Counter { | |
176 | Counter { i: 0 } | |
177 | } | |
178 | } | |
179 | impl SeedableRng<u32> for Counter { | |
180 | fn reseed(&mut self, seed: u32) { | |
181 | self.i = seed; | |
182 | } | |
183 | fn from_seed(seed: u32) -> Counter { | |
184 | Counter { i: seed } | |
185 | } | |
186 | } | |
187 | type MyRng = ReseedingRng<Counter, ReseedWithDefault>; | |
188 | ||
189 | #[test] | |
190 | fn test_reseeding() { | |
191 | let mut rs = ReseedingRng::new(Counter {i:0}, 400, ReseedWithDefault); | |
192 | ||
193 | let mut i = 0; | |
85aaf69f | 194 | for _ in 0..1000 { |
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195 | assert_eq!(rs.next_u32(), i % 100); |
196 | i += 1; | |
197 | } | |
198 | } | |
199 | ||
200 | #[test] | |
201 | fn test_rng_seeded() { | |
202 | let mut ra: MyRng = SeedableRng::from_seed((ReseedWithDefault, 2)); | |
203 | let mut rb: MyRng = SeedableRng::from_seed((ReseedWithDefault, 2)); | |
204 | assert!(order::equals(ra.gen_ascii_chars().take(100), | |
205 | rb.gen_ascii_chars().take(100))); | |
206 | } | |
207 | ||
208 | #[test] | |
209 | fn test_rng_reseed() { | |
210 | let mut r: MyRng = SeedableRng::from_seed((ReseedWithDefault, 3)); | |
211 | let string1: String = r.gen_ascii_chars().take(100).collect(); | |
212 | ||
213 | r.reseed((ReseedWithDefault, 3)); | |
214 | ||
215 | let string2: String = r.gen_ascii_chars().take(100).collect(); | |
216 | assert_eq!(string1, string2); | |
217 | } | |
218 | ||
219 | static FILL_BYTES_V_LEN: uint = 13579; | |
220 | #[test] | |
221 | fn test_rng_fill_bytes() { | |
222 | let mut v = repeat(0u8).take(FILL_BYTES_V_LEN).collect::<Vec<_>>(); | |
85aaf69f | 223 | ::test::rng().fill_bytes(&mut v); |
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224 | |
225 | // Sanity test: if we've gotten here, `fill_bytes` has not infinitely | |
226 | // recursed. | |
227 | assert_eq!(v.len(), FILL_BYTES_V_LEN); | |
228 | ||
229 | // To test that `fill_bytes` actually did something, check that the | |
230 | // average of `v` is not 0. | |
231 | let mut sum = 0.0; | |
85aaf69f | 232 | for &x in &v { |
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233 | sum += x as f64; |
234 | } | |
235 | assert!(sum / v.len() as f64 != 0.0); | |
236 | } | |
237 | } |