# [−][src]Struct rand_isaac::isaac::IsaacRng

`pub struct 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

1. Bob Jenkins, ISAAC and RC4

2. Jean-Philippe Aumasson, On the pseudo-random generator ISAAC

## Trait Implementations

### `impl SeedableRng for IsaacRng`[src]

#### `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 seed_from_u64(seed: u64) -> Self`[src]

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.

## Blanket Implementations

### `impl<T, U> TryFrom<U> for T where    U: Into<T>, `[src]

#### `type Error = Infallible`

The type returned in the event of a conversion error.

### `impl<T, U> TryInto<U> for T where    U: TryFrom<T>, `[src]

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

The type returned in the event of a conversion error.

### `impl<T> ToOwned for T where    T: Clone, `[src]

#### `type Owned = T`

The resulting type after obtaining ownership.