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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 | ||
1a4d82fc | 14 | use {Rng, SeedableRng}; |
1a4d82fc JJ |
15 | |
16 | /// How many bytes of entropy the underling RNG is allowed to generate | |
17 | /// before it is reseeded. | |
c34b1796 | 18 | const DEFAULT_GENERATION_THRESHOLD: usize = 32 * 1024; |
1a4d82fc JJ |
19 | |
20 | /// A wrapper around any RNG which reseeds the underlying RNG after it | |
21 | /// has generated a certain number of random bytes. | |
22 | pub struct ReseedingRng<R, Rsdr> { | |
23 | rng: R, | |
c34b1796 AL |
24 | generation_threshold: usize, |
25 | bytes_generated: usize, | |
1a4d82fc JJ |
26 | /// Controls the behaviour when reseeding the RNG. |
27 | pub reseeder: Rsdr, | |
28 | } | |
29 | ||
30 | impl<R: Rng, Rsdr: Reseeder<R>> ReseedingRng<R, Rsdr> { | |
31 | /// Create a new `ReseedingRng` with the given parameters. | |
32 | /// | |
33 | /// # Arguments | |
34 | /// | |
35 | /// * `rng`: the random number generator to use. | |
36 | /// * `generation_threshold`: the number of bytes of entropy at which to reseed the RNG. | |
37 | /// * `reseeder`: the reseeding object to use. | |
b039eaaf | 38 | pub fn new(rng: R, generation_threshold: usize, reseeder: Rsdr) -> ReseedingRng<R, Rsdr> { |
1a4d82fc JJ |
39 | ReseedingRng { |
40 | rng: rng, | |
41 | generation_threshold: generation_threshold, | |
42 | bytes_generated: 0, | |
b039eaaf | 43 | reseeder: reseeder, |
1a4d82fc JJ |
44 | } |
45 | } | |
46 | ||
47 | /// Reseed the internal RNG if the number of bytes that have been | |
48 | /// generated exceed the threshold. | |
49 | pub fn reseed_if_necessary(&mut self) { | |
50 | if self.bytes_generated >= self.generation_threshold { | |
51 | self.reseeder.reseed(&mut self.rng); | |
52 | self.bytes_generated = 0; | |
53 | } | |
54 | } | |
55 | } | |
56 | ||
57 | ||
58 | impl<R: Rng, Rsdr: Reseeder<R>> Rng for ReseedingRng<R, Rsdr> { | |
59 | fn next_u32(&mut self) -> u32 { | |
60 | self.reseed_if_necessary(); | |
61 | self.bytes_generated += 4; | |
62 | self.rng.next_u32() | |
63 | } | |
64 | ||
65 | fn next_u64(&mut self) -> u64 { | |
66 | self.reseed_if_necessary(); | |
67 | self.bytes_generated += 8; | |
68 | self.rng.next_u64() | |
69 | } | |
70 | ||
71 | fn fill_bytes(&mut self, dest: &mut [u8]) { | |
72 | self.reseed_if_necessary(); | |
73 | self.bytes_generated += dest.len(); | |
74 | self.rng.fill_bytes(dest) | |
75 | } | |
76 | } | |
77 | ||
78 | impl<S, R: SeedableRng<S>, Rsdr: Reseeder<R> + Default> | |
79 | SeedableRng<(Rsdr, S)> for ReseedingRng<R, Rsdr> { | |
80 | fn reseed(&mut self, (rsdr, seed): (Rsdr, S)) { | |
81 | self.rng.reseed(seed); | |
82 | self.reseeder = rsdr; | |
83 | self.bytes_generated = 0; | |
84 | } | |
85 | ||
86 | /// Create a new `ReseedingRng` from the given reseeder and | |
87 | /// seed. This uses a default value for `generation_threshold`. | |
88 | fn from_seed((rsdr, seed): (Rsdr, S)) -> ReseedingRng<R, Rsdr> { | |
89 | ReseedingRng { | |
90 | rng: SeedableRng::from_seed(seed), | |
91 | generation_threshold: DEFAULT_GENERATION_THRESHOLD, | |
92 | bytes_generated: 0, | |
b039eaaf | 93 | reseeder: rsdr, |
1a4d82fc JJ |
94 | } |
95 | } | |
96 | } | |
97 | ||
98 | /// Something that can be used to reseed an RNG via `ReseedingRng`. | |
1a4d82fc JJ |
99 | pub trait Reseeder<R> { |
100 | /// Reseed the given RNG. | |
101 | fn reseed(&mut self, rng: &mut R); | |
102 | } | |
103 | ||
104 | /// Reseed an RNG using a `Default` instance. This reseeds by | |
105 | /// replacing the RNG with the result of a `Default::default` call. | |
c34b1796 AL |
106 | #[derive(Copy, Clone)] |
107 | pub struct ReseedWithDefault; | |
1a4d82fc JJ |
108 | |
109 | impl<R: Rng + Default> Reseeder<R> for ReseedWithDefault { | |
110 | fn reseed(&mut self, rng: &mut R) { | |
111 | *rng = Default::default(); | |
112 | } | |
113 | } | |
85aaf69f | 114 | #[stable(feature = "rust1", since = "1.0.0")] |
1a4d82fc | 115 | impl Default for ReseedWithDefault { |
b039eaaf SL |
116 | fn default() -> ReseedWithDefault { |
117 | ReseedWithDefault | |
118 | } | |
1a4d82fc JJ |
119 | } |
120 | ||
121 | #[cfg(test)] | |
d9579d0f | 122 | mod tests { |
1a4d82fc JJ |
123 | use std::prelude::v1::*; |
124 | ||
b039eaaf | 125 | use core::iter::order; |
1a4d82fc | 126 | use super::{ReseedingRng, ReseedWithDefault}; |
1a4d82fc JJ |
127 | use {SeedableRng, Rng}; |
128 | ||
129 | struct Counter { | |
b039eaaf | 130 | i: u32, |
1a4d82fc JJ |
131 | } |
132 | ||
133 | impl Rng for Counter { | |
134 | fn next_u32(&mut self) -> u32 { | |
135 | self.i += 1; | |
136 | // very random | |
137 | self.i - 1 | |
138 | } | |
139 | } | |
140 | impl Default for Counter { | |
141 | fn default() -> Counter { | |
142 | Counter { i: 0 } | |
143 | } | |
144 | } | |
145 | impl SeedableRng<u32> for Counter { | |
146 | fn reseed(&mut self, seed: u32) { | |
147 | self.i = seed; | |
148 | } | |
149 | fn from_seed(seed: u32) -> Counter { | |
150 | Counter { i: seed } | |
151 | } | |
152 | } | |
153 | type MyRng = ReseedingRng<Counter, ReseedWithDefault>; | |
154 | ||
155 | #[test] | |
156 | fn test_reseeding() { | |
b039eaaf | 157 | let mut rs = ReseedingRng::new(Counter { i: 0 }, 400, ReseedWithDefault); |
1a4d82fc JJ |
158 | |
159 | let mut i = 0; | |
85aaf69f | 160 | for _ in 0..1000 { |
1a4d82fc JJ |
161 | assert_eq!(rs.next_u32(), i % 100); |
162 | i += 1; | |
163 | } | |
164 | } | |
165 | ||
166 | #[test] | |
167 | fn test_rng_seeded() { | |
168 | let mut ra: MyRng = SeedableRng::from_seed((ReseedWithDefault, 2)); | |
169 | let mut rb: MyRng = SeedableRng::from_seed((ReseedWithDefault, 2)); | |
170 | assert!(order::equals(ra.gen_ascii_chars().take(100), | |
171 | rb.gen_ascii_chars().take(100))); | |
172 | } | |
173 | ||
174 | #[test] | |
175 | fn test_rng_reseed() { | |
176 | let mut r: MyRng = SeedableRng::from_seed((ReseedWithDefault, 3)); | |
177 | let string1: String = r.gen_ascii_chars().take(100).collect(); | |
178 | ||
179 | r.reseed((ReseedWithDefault, 3)); | |
180 | ||
181 | let string2: String = r.gen_ascii_chars().take(100).collect(); | |
182 | assert_eq!(string1, string2); | |
183 | } | |
184 | ||
c34b1796 | 185 | const FILL_BYTES_V_LEN: usize = 13579; |
1a4d82fc JJ |
186 | #[test] |
187 | fn test_rng_fill_bytes() { | |
c1a9b12d | 188 | let mut v = vec![0; FILL_BYTES_V_LEN]; |
85aaf69f | 189 | ::test::rng().fill_bytes(&mut v); |
1a4d82fc JJ |
190 | |
191 | // Sanity test: if we've gotten here, `fill_bytes` has not infinitely | |
192 | // recursed. | |
193 | assert_eq!(v.len(), FILL_BYTES_V_LEN); | |
194 | ||
195 | // To test that `fill_bytes` actually did something, check that the | |
196 | // average of `v` is not 0. | |
197 | let mut sum = 0.0; | |
85aaf69f | 198 | for &x in &v { |
1a4d82fc JJ |
199 | sum += x as f64; |
200 | } | |
201 | assert!(sum / v.len() as f64 != 0.0); | |
202 | } | |
203 | } |