Struct rand::prng::isaac::IsaacRng[][src]

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 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

Methods

impl IsaacRng
[src]

Deprecated since 0.5.0

: use the FromEntropy or SeedableRng trait

Create an ISAAC random number generator using the default fixed seed.

DEPRECATED. IsaacRng::new_from_u64(0) will produce identical results.

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

impl Clone for IsaacRng
[src]

Returns a copy of the value. Read more

Performs copy-assignment from source. Read more

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

impl RngCore for IsaacRng
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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

impl SeedableRng for IsaacRng
[src]

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

Create a new PRNG using a u64 seed. Read more

Auto Trait Implementations

impl Send for IsaacRng

impl Sync for IsaacRng