Trait rand::Rng [−] [src]

pub trait Rng {
    fn next_u32(&mut self) -> u32;

    fn next_u64(&mut self) -> u64 { ... }

    fn next_f32(&mut self) -> f32 { ... }

    fn next_f64(&mut self) -> f64 { ... }

    fn fill_bytes(&mut self, dest: &mut [u8]) { ... }

    fn try_fill_bytes(&mut self, dest: &mut [u8]) -> Result<(), Error> { ... }
}

A random number generator.

This trait encapsulates the low-level functionality common to all generators, and is the "back end", to be implemented by generators. Several extension traits exist:

Required Methods

Return the next random u32.

Implementations of this trait must implement at least one of next_u32, next_u64 and fill_bytes directly. In the case this function is not implemented directly, it can be implemented using self.next_u64() as u32 or via fill_bytes (TODO: expose helper function).

Provided Methods

Return the next random u64.

Implementations of this trait must implement at least one of next_u32, next_u64 and fill_bytes directly. In the case this function is not implemented directly, the default implementation will generate values via next_u32 in little-endian fashion, or this function can be implemented via fill_bytes (TODO: expose helper function).

Types wrapping an inner RNG must not use the default implementation, since the inner RNG's implementation may produce different values.

Return the next random f32 selected from the half-open interval [0, 1).

This uses a technique described by Saito and Matsumoto at MCQMC'08. Given that the IEEE floating point numbers are uniformly distributed over [1,2), we generate a number in this range and then offset it onto the range [0,1). Our choice of bits (masking v. shifting) is arbitrary and should be immaterial for high quality generators. For low quality generators (ex. LCG), prefer bitshifting due to correlation between sequential low order bits.

See: A PRNG specialized in double precision floating point numbers using an affine transition

By default this is implemented in terms of next_u32, but a random number generator which can generate numbers satisfying the requirements directly can overload this for performance. It is required that the return value lies in [0, 1).

See Closed01 for the closed interval [0,1], and Open01 for the open interval (0,1).

Return the next random f64 selected from the half-open interval [0, 1).

By default this is implemented in terms of next_u64, but a random number generator which can generate numbers satisfying the requirements directly can overload this for performance. It is required that the return value lies in [0, 1).

See Closed01 for the closed interval [0,1], and Open01 for the open interval (0,1).

Fill dest with random data.

Implementations of this trait must implement at least one of next_u32, next_u64 and fill_bytes directly. In the case this function is not implemented directly, the default implementation will generate values via next_u64 in little-endian fashion. (TODO: expose helper function to allow implementation via next_u32.)

There is no requirement on how this method generates values relative to next_u32 or next_u64; e.g. a u64 cast to bytes is not required to have the same value as eight bytes filled via this function. There is a requirement of portability for reproducible generators which implies that any seedable generator must fix endianness when generating bytes.

Types wrapping an inner RNG must not use the default implementation, since the inner RNG's implementation may produce different values.

This method should guarantee that dest is entirely filled with new data, and may panic if this is impossible (e.g. reading past the end of a file that is being used as the source of randomness).

Example

use rand::{thread_rng, Rng};

let mut v = [0u8; 13579];
thread_rng().fill_bytes(&mut v);
println!("{:?}", &v[..]);

Fill dest entirely with random data.

This is the only method which allows an RNG to report errors while generating random data; other methods either handle the error internally or panic. This method is the intended way to use external (true) RNGs, like OsRng. Its main use-cases are to generate keys and to seed (infallible) PRNGs.

Other than error handling, this method is identical to fill_bytes, and has a default implementation simply wrapping fill_bytes.

Implementations on Foreign Types

impl<'a, R: ?Sized> Rng for &'a mut R where
    R: Rng, 
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impl<R: ?Sized> Rng for Box<R> where
    R: Rng, 
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Implementors