src/vendor/rand-0.4.2/src/reseeding.rs

   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::default::Default;
  15
  16 use {Rng, SeedableRng};
  17
  18 /// How many bytes of entropy the underling RNG is allowed to generate
  19 /// before it is reseeded
  20 const DEFAULT_GENERATION_THRESHOLD: u64 = 32 * 1024;
  21
  22 /// A wrapper around any RNG which reseeds the underlying RNG after it
  23 /// has generated a certain number of random bytes.
  24 #[derive(Debug)]
  25 pub struct ReseedingRng<R, Rsdr> {
  26     rng: R,
  27     generation_threshold: u64,
  28     bytes_generated: u64,
  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: u64, 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() as u64;
  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 rand::{Rng, SeedableRng, StdRng};
 107 /// use 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(Clone, Copy, Debug)]
 137 pub struct ReseedWithDefault;
 138
 139 impl<R: Rng + Default> Reseeder<R> for ReseedWithDefault {
 140     fn reseed(&mut self, rng: &mut R) {
 141         *rng = Default::default();
 142     }
 143 }
 144 impl Default for ReseedWithDefault {
 145     fn default() -> ReseedWithDefault { ReseedWithDefault }
 146 }
 147
 148 #[cfg(test)]
 149 mod test {
 150     use std::default::Default;
 151     use std::iter::repeat;
 152     use super::{ReseedingRng, ReseedWithDefault};
 153     use {SeedableRng, Rng};
 154
 155     struct Counter {
 156         i: u32
 157     }
 158
 159     impl Rng for Counter {
 160         fn next_u32(&mut self) -> u32 {
 161             self.i += 1;
 162             // very random
 163             self.i - 1
 164         }
 165     }
 166     impl Default for Counter {
 167         fn default() -> Counter {
 168             Counter { i: 0 }
 169         }
 170     }
 171     impl SeedableRng<u32> for Counter {
 172         fn reseed(&mut self, seed: u32) {
 173             self.i = seed;
 174         }
 175         fn from_seed(seed: u32) -> Counter {
 176             Counter { i: seed }
 177         }
 178     }
 179     type MyRng = ReseedingRng<Counter, ReseedWithDefault>;
 180
 181     #[test]
 182     fn test_reseeding() {
 183         let mut rs = ReseedingRng::new(Counter {i:0}, 400, ReseedWithDefault);
 184
 185         let mut i = 0;
 186         for _ in 0..1000 {
 187             assert_eq!(rs.next_u32(), i % 100);
 188             i += 1;
 189         }
 190     }
 191
 192     #[test]
 193     fn test_rng_seeded() {
 194         let mut ra: MyRng = SeedableRng::from_seed((ReseedWithDefault, 2));
 195         let mut rb: MyRng = SeedableRng::from_seed((ReseedWithDefault, 2));
 196         assert!(::test::iter_eq(ra.gen_ascii_chars().take(100),
 197                                 rb.gen_ascii_chars().take(100)));
 198     }
 199
 200     #[test]
 201     fn test_rng_reseed() {
 202         let mut r: MyRng = SeedableRng::from_seed((ReseedWithDefault, 3));
 203         let string1: String = r.gen_ascii_chars().take(100).collect();
 204
 205         r.reseed((ReseedWithDefault, 3));
 206
 207         let string2: String = r.gen_ascii_chars().take(100).collect();
 208         assert_eq!(string1, string2);
 209     }
 210
 211     const FILL_BYTES_V_LEN: usize = 13579;
 212     #[test]
 213     fn test_rng_fill_bytes() {
 214         let mut v = repeat(0u8).take(FILL_BYTES_V_LEN).collect::<Vec<_>>();
 215         ::test::rng().fill_bytes(&mut v);
 216
 217         // Sanity test: if we've gotten here, `fill_bytes` has not infinitely
 218         // recursed.
 219         assert_eq!(v.len(), FILL_BYTES_V_LEN);
 220
 221         // To test that `fill_bytes` actually did something, check that the
 222         // average of `v` is not 0.
 223         let mut sum = 0.0;
 224         for &x in v.iter() {
 225             sum += x as f64;
 226         }
 227         assert!(sum / v.len() as f64 != 0.0);
 228     }
 229 }