[−][src]Struct rand_isaac::isaac::IsaacRng
A random number generator that uses the ISAAC algorithm.
ISAAC stands for "Indirection, Shift, Accumulate, Add, and Count" which are the principal bitwise operations employed. It is the most advanced of a series of array based random number generator designed by Robert Jenkins in 199612.
ISAAC is notably fast and produces excellent quality random numbers for non-cryptographic applications.
In spite of being designed with cryptographic security in mind, ISAAC hasn't
been stringently cryptanalyzed and thus cryptographers do not not
consensually trust it to be secure. When looking for a secure RNG, prefer
Hc128Rng
from the rand_hc
crate instead, which, like ISAAC, is an
array-based RNG and one of the stream-ciphers selected the by eSTREAM
In 2006 an improvement to ISAAC was suggested by Jean-Philippe Aumasson, named ISAAC+3. But because the specification is not complete, because there is no good implementation, and because the suggested bias may not exist, it is not implemented here.
Overview of the ISAAC algorithm:
(in pseudo-code)
Input: a, b, c, s[256] // state
Output: r[256] // results
mix(a,i) = a ^ a << 13 if i = 0 mod 4
a ^ a >> 6 if i = 1 mod 4
a ^ a << 2 if i = 2 mod 4
a ^ a >> 16 if i = 3 mod 4
c = c + 1
b = b + c
for i in 0..256 {
x = s_[i]
a = f(a,i) + s[i+128 mod 256]
y = a + b + s[x>>2 mod 256]
s[i] = y
b = x + s[y>>10 mod 256]
r[i] = b
}
Numbers are generated in blocks of 256. This means the function above only runs once every 256 times you ask for a next random number. In all other circumstances the last element of the results array is returned.
ISAAC therefore needs a lot of memory, relative to other non-crypto RNGs. 2 * 256 * 4 = 2 kb to hold the state and results.
This implementation uses BlockRng
to implement the RngCore
methods.
References
Bob Jenkins, ISAAC: A fast cryptographic random number generator ↩
Bob Jenkins, ISAAC and RC4 ↩
Jean-Philippe Aumasson, On the pseudo-random generator ISAAC ↩
Trait Implementations
impl Clone for IsaacRng
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pub fn clone(&self) -> IsaacRng
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pub fn clone_from(&mut self, source: &Self)
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impl Debug for IsaacRng
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impl RngCore for IsaacRng
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pub fn next_u32(&mut self) -> u32
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pub fn next_u64(&mut self) -> u64
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pub fn fill_bytes(&mut self, dest: &mut [u8])
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pub fn try_fill_bytes(&mut self, dest: &mut [u8]) -> Result<(), Error>
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impl SeedableRng for IsaacRng
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type Seed = <IsaacCore as SeedableRng>::Seed
Seed type, which is restricted to types mutably-dereferencable as u8
arrays (we recommend [u8; N]
for some N
). Read more
pub fn from_seed(seed: Self::Seed) -> Self
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pub fn seed_from_u64(seed: u64) -> Self
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Create an ISAAC random number generator using an u64
as seed.
If seed == 0
this will produce the same stream of random numbers as
the reference implementation when used unseeded.
pub fn from_rng<S: RngCore>(rng: S) -> Result<Self, Error>
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Auto Trait Implementations
Blanket Implementations
impl<T> Any for T where
T: 'static + ?Sized,
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T: 'static + ?Sized,
impl<T> Borrow<T> for T where
T: ?Sized,
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T: ?Sized,
impl<T> BorrowMut<T> for T where
T: ?Sized,
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T: ?Sized,
pub fn borrow_mut(&mut self) -> &mut T
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impl<T> From<T> for T
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impl<T, U> Into<U> for T where
U: From<T>,
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U: From<T>,
impl<T, U> TryFrom<U> for T where
U: Into<T>,
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U: Into<T>,
type Error = Infallible
The type returned in the event of a conversion error.
pub fn try_from(value: U) -> Result<T, <T as TryFrom<U>>::Error>
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impl<T, U> TryInto<U> for T where
U: TryFrom<T>,
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U: TryFrom<T>,