# [−][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 1996^{1}^{2}.

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 Debug for IsaacRng`

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`impl Clone for IsaacRng`

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`fn clone(&self) -> IsaacRng`

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`fn clone_from(&mut self, source: &Self)`

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Performs copy-assignment from `source`

. Read more

`impl Serialize for IsaacRng`

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`fn serialize<__S>(&self, __serializer: __S) -> Result<__S::Ok, __S::Error> where`

__S: Serializer,

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__S: Serializer,

`impl<'de> Deserialize<'de> for IsaacRng`

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`fn deserialize<__D>(__deserializer: __D) -> Result<Self, __D::Error> where`

__D: Deserializer<'de>,

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__D: Deserializer<'de>,

`impl RngCore for IsaacRng`

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`fn next_u32(&mut self) -> u32`

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`fn next_u64(&mut self) -> u64`

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`fn fill_bytes(&mut self, dest: &mut [u8])`

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`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

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

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`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.

`fn from_rng<S: RngCore>(rng: S) -> Result<Self, Error>`

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`fn from_entropy() -> Self`

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Creates a new instance of the RNG seeded via [`getrandom`

]. Read more

## Auto Trait Implementations

`impl Send for IsaacRng`

`impl Sync for IsaacRng`

`impl Unpin for IsaacRng`

`impl UnwindSafe for IsaacRng`

`impl RefUnwindSafe for IsaacRng`

## Blanket Implementations

`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.

`fn try_from(value: U) -> Result<T, <T as TryFrom<U>>::Error>`

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`impl<T, U> Into<U> for T where`

U: From<T>,

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U: From<T>,

`impl<T> From<T> for T`

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`impl<T, U> TryInto<U> for T where`

U: TryFrom<T>,

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U: TryFrom<T>,

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

The type returned in the event of a conversion error.

`fn try_into(self) -> Result<U, <U as TryFrom<T>>::Error>`

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`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,

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

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`impl<T> Any for T where`

T: 'static + ?Sized,

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T: 'static + ?Sized,

`impl<T> ToOwned for T where`

T: Clone,

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T: Clone,

`type Owned = T`

The resulting type after obtaining ownership.

`fn to_owned(&self) -> T`

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`fn clone_into(&self, target: &mut T)`

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`impl<T> DeserializeOwned for T where`

T: Deserialize<'de>,

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T: Deserialize<'de>,