# Struct rand_isaac::isaac::IsaacRng

``pub struct IsaacRng(_);``
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

1. Bob Jenkins, ISAAC and RC4

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

## Implementations

👎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.

## Trait Implementations

Returns a copy of the value. Read more
Performs copy-assignment from `source`. Read more
Formats the value using the given formatter. Read more
Return the next random `u32`. Read more
Return the next random `u64`. Read more
Fill `dest` with random data. Read more
Fill `dest` entirely with random data. Read more

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.

Seed type, which is restricted to types mutably-dereferencable as `u8` arrays (we recommend `[u8; N]` for some `N`). Read more
Create a new PRNG using the given seed. Read more
Create a new PRNG seeded from another `Rng`. Read more

## Blanket Implementations

Gets the `TypeId` of `self`. Read more
Immutably borrows from an owned value. Read more
Mutably borrows from an owned value. Read more

Returns the argument unchanged.

Calls `U::from(self)`.

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

The type returned in the event of a conversion error.
Performs the conversion.
The type returned in the event of a conversion error.
Performs the conversion.