rand_isaac::isaac

Struct IsaacRng

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pub struct IsaacRng(/* private fields */);
Expand description

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 instead, which, like ISAAC, is an array-based RNG and one of the stream-ciphers selected the by eSTREAM contest.

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

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impl IsaacRng

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pub fn new_from_u64(seed: u64) -> Self

👎Deprecated since 0.6.0: use SeedableRng::seed_from_u64 instead

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.

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impl Clone for IsaacRng

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fn clone(&self) -> IsaacRng

Returns a copy of the value. Read more
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fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source. Read more
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impl Debug for IsaacRng

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fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter. Read more
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impl RngCore for IsaacRng

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fn next_u32(&mut self) -> u32

Return the next random u32. Read more
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fn next_u64(&mut self) -> u64

Return the next random u64. Read more
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fn fill_bytes(&mut self, dest: &mut [u8])

Fill dest with random data. Read more
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fn try_fill_bytes(&mut self, dest: &mut [u8]) -> Result<(), Error>

Fill dest entirely with random data. Read more
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impl SeedableRng for IsaacRng

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fn seed_from_u64(seed: u64) -> Self

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.

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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
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fn from_seed(seed: Self::Seed) -> Self

Create a new PRNG using the given seed. Read more
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fn from_rng<S: RngCore>(rng: S) -> Result<Self, Error>

Create a new PRNG seeded from another Rng. Read more

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impl<T> Any for T
where T: 'static + ?Sized,

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fn type_id(&self) -> TypeId

Gets the TypeId of self. Read more
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impl<T> Borrow<T> for T
where T: ?Sized,

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fn borrow(&self) -> &T

Immutably borrows from an owned value. Read more
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impl<T> BorrowMut<T> for T
where T: ?Sized,

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fn borrow_mut(&mut self) -> &mut T

Mutably borrows from an owned value. Read more
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impl<T> CloneToUninit for T
where T: Clone,

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unsafe fn clone_to_uninit(&self, dst: *mut T)

🔬This is a nightly-only experimental API. (clone_to_uninit)
Performs copy-assignment from self to dst. Read more
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impl<T> From<T> for T

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fn from(t: T) -> T

Returns the argument unchanged.

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impl<T, U> Into<U> for T
where U: From<T>,

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fn into(self) -> U

Calls U::from(self).

That is, this conversion is whatever the implementation of From<T> for U chooses to do.

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impl<T, U> TryFrom<U> for T
where U: Into<T>,

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type Error = Infallible

The type returned in the event of a conversion error.
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fn try_from(value: U) -> Result<T, <T as TryFrom<U>>::Error>

Performs the conversion.
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impl<T, U> TryInto<U> for T
where U: TryFrom<T>,

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type Error = <U as TryFrom<T>>::Error

The type returned in the event of a conversion error.
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fn try_into(self) -> Result<U, <U as TryFrom<T>>::Error>

Performs the conversion.