# Struct rand_isaac::isaac64::Isaac64Rng

source · `pub struct Isaac64Rng(_);`

## Expand description

A random number generator that uses ISAAC-64, the 64-bit variant of 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}.

ISAAC-64 is mostly similar to ISAAC. Because it operates on 64-bit integers instead of 32-bit, it uses twice as much memory to hold its state and results. Also it uses different constants for shifts and indirect indexing, optimized to give good results for 64bit arithmetic.

ISAAC-64 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.

### Overview of the ISAAC-64 algorithm:

(in pseudo-code)

```
Input: a, b, c, s[256] // state
Output: r[256] // results
mix(a,i) = !(a ^ a << 21) if i = 0 mod 4
a ^ a >> 5 if i = 1 mod 4
a ^ a << 12 if i = 2 mod 4
a ^ a >> 33 if i = 3 mod 4
c = c + 1
b = b + c
for i in 0..256 {
x = s_[i]
a = mix(a,i) + s[i+128 mod 256]
y = a + b + s[x>>3 mod 256]
s[i] = y
b = x + s[y>>11 mod 256]
r[i] = b
}
```

This implementation uses `BlockRng64`

to implement the `RngCore`

methods.

See for more information the documentation of `IsaacRng`

.

Bob Jenkins,

*ISAAC and RC4*↩

## Implementations

source### impl Isaac64Rng

### impl Isaac64Rng

source#### pub fn new_from_u64(seed: u64) -> Self

👎Deprecated since 0.6.0: use SeedableRng::seed_from_u64 instead

#### pub fn new_from_u64(seed: u64) -> Self

Create an ISAAC-64 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

source### impl Clone for Isaac64Rng

### impl Clone for Isaac64Rng

source#### fn clone(&self) -> Isaac64Rng

#### fn clone(&self) -> Isaac64Rng

1.0.0 · source#### fn clone_from(&mut self, source: &Self)

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

`source`

. Read moresource### impl Debug for Isaac64Rng

### impl Debug for Isaac64Rng

source### impl RngCore for Isaac64Rng

### impl RngCore for Isaac64Rng

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

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

`dest`

with random data. Read moresource### impl SeedableRng for Isaac64Rng

### impl SeedableRng for Isaac64Rng

source#### fn seed_from_u64(seed: u64) -> Self

#### 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.

#### type Seed = <Isaac64Core as SeedableRng>::Seed

#### type Seed = <Isaac64Core as SeedableRng>::Seed

`u8`

arrays (we recommend `[u8; N]`

for some `N`

). Read more