92725ae765
This provides 2 methods: .reseed() and ::from_seed that modify and create respecitively. Implement this trait for the RNGs in the stdlib for which this makes sense.
131 lines
3.6 KiB
Rust
131 lines
3.6 KiB
Rust
// Copyright 2013 The Rust Project Developers. See the COPYRIGHT
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// file at the top-level directory of this distribution and at
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// http://rust-lang.org/COPYRIGHT.
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//
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// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
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// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
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// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
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// option. This file may not be copied, modified, or distributed
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// except according to those terms.
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//! A wrapper around another RNG that reseeds it after it
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//! generates a certain number of random bytes.
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use rand::Rng;
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use default::Default;
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/// How many bytes of entropy the underling RNG is allowed to generate
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/// before it is reseeded.
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static DEFAULT_GENERATION_THRESHOLD: uint = 32 * 1024;
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/// A wrapper around any RNG which reseeds the underlying RNG after it
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/// has generated a certain number of random bytes.
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pub struct ReseedingRng<R, Rsdr> {
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priv rng: R,
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priv generation_threshold: uint,
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priv bytes_generated: uint,
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/// Controls the behaviour when reseeding the RNG.
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reseeder: Rsdr
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}
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impl<R: Rng, Rsdr: Reseeder<R>> ReseedingRng<R, Rsdr> {
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/// Create a new `ReseedingRng` with the given parameters.
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///
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/// # Arguments
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///
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/// * `rng`: the random number generator to use.
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/// * `generation_threshold`: the number of bytes of entropy at which to reseed the RNG.
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/// * `reseeder`: the reseeding object to use.
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pub fn new(rng: R, generation_threshold: uint, reseeder: Rsdr) -> ReseedingRng<R,Rsdr> {
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ReseedingRng {
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rng: rng,
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generation_threshold: generation_threshold,
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bytes_generated: 0,
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reseeder: reseeder
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}
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}
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/// Reseed the internal RNG if the number of bytes that have been
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/// generated exceed the threshold.
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pub fn reseed_if_necessary(&mut self) {
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if self.bytes_generated >= self.generation_threshold {
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self.reseeder.reseed(&mut self.rng);
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self.bytes_generated = 0;
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}
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}
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}
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impl<R: Rng, Rsdr: Reseeder<R>> Rng for ReseedingRng<R, Rsdr> {
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fn next_u32(&mut self) -> u32 {
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self.reseed_if_necessary();
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self.bytes_generated += 4;
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self.rng.next_u32()
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}
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fn next_u64(&mut self) -> u64 {
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self.reseed_if_necessary();
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self.bytes_generated += 8;
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self.rng.next_u64()
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}
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fn fill_bytes(&mut self, dest: &mut [u8]) {
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self.reseed_if_necessary();
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self.bytes_generated += dest.len();
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self.fill_bytes(dest)
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}
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}
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/// Something that can be used to reseed an RNG via `ReseedingRng`.
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pub trait Reseeder<R> {
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/// Reseed the given RNG.
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fn reseed(&mut self, rng: &mut R);
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}
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/// Reseed an RNG using a `Default` instance. This reseeds by
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/// replacing the RNG with the result of a `Default::default` call.
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pub struct ReseedWithDefault;
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impl<R: Rng + Default> Reseeder<R> for ReseedWithDefault {
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fn reseed(&mut self, rng: &mut R) {
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*rng = Default::default();
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}
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}
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#[cfg(test)]
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mod test {
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use super::*;
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use rand::Rng;
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use default::Default;
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use iter::range;
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use option::{None, Some};
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struct Counter {
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i: u32
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}
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impl Rng for Counter {
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fn next_u32(&mut self) -> u32 {
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self.i += 1;
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// very random
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self.i - 1
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}
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}
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impl Default for Counter {
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fn default() -> Counter {
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Counter { i: 0 }
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}
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}
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#[test]
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fn test_reseeding() {
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let mut rs = ReseedingRng::new(Counter {i:0}, 400, ReseedWithDefault);
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let mut i = 0;
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for _ in range(0, 1000) {
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assert_eq!(rs.next_u32(), i % 100);
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i += 1;
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}
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}
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}
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