module Random

Overview

Random provides an interface for random values generation, using a pseudo random number generator (PRNG).

Random.rand    # => 0.167595
Random.rand(5) # => 2

The above methods delegate to a Random instance.

r = Random.new
r.rand      # => 0.0372991
r.next_bool # => true
r.next_int  # => 2223112

This module also defines a global method #rand, which Array#sample and Array#shuffle delegates.

rand     # => 0.293829
rand(10) # => 8

An instance of each class that includes Random is a random number generator with its own state. Usually such RNGs can be initialized with a seed, which defines their initial state. It is guaranteed that after initializing two different instances with the same seed, and then executing the same calls on both of them, you will get the same results. This allows exactly reproducing the same seemingly random events by just keeping the seed.

It is possible to make a custom RNG by including Random and implementing #next_u to return an unsigned number of a pre-determined type (usually UInt32). The numbers generated by your RNG must be uniformly distributed in the whole range of possible values for that type (e.g. 0u32..UInt32::MAX). This allows all other methods of Random to be based on this and still produce uniformly distributed results. Your Random class should also have a way to initialize it. For pseudo-random number generators that will usually be an integer seed, but there are no rigid requirements for the initialization.

The default PRNG is Random::PCG32 which has a good overall statistical distribution (low bias of generated numbers) and is fast for overall usages on different platforms, but isn't cryptographically secure. If a third party has access to some generated numbers, she may deduce incoming numbers, putting your application at risk.

It is recommended to use a secure source, such as Random::Secure, Random::ISAAC or ChaCha20 for anything that needs security, such as online games, identification tokens, salts, initializing a PRNG, ... These PRNG are slower but cryptographically secure, so a third party can't deduce incoming numbers.

Direct including types

• Random::ISAAC
• Random::PCG32

Defined in:

Constant Summary

DEFAULT = PCG32.new

Constructors

• .new(seed, sequence = 0_u64)

  Initializes an instance with the given seed and sequence.

• .new

  Initializes an instance seeded from a system source.

Class Method Summary

• .rand(x)

  See #rand(x).

• .rand : Float64

  See #rand.

Instance Method Summary

• #base64(n : Int = 16) : String

  Generates n random bytes that are encoded into base64.

• #hex(n : Int = 16) : String

  Generates a hexadecimal string based on n random bytes.

• #next_bool : Bool

  Generates a random Bool.

• #next_float : Float64

  See #rand.

• #next_int : Int32

  Same as #rand(Int32::MIN..Int32::MAX).

• #next_u : UInt

  Generates a random unsigned integer.

• #rand(max : Int) : Int

  Generates a random integer which is greater than or equal to 0 and less than max.

• #rand(max : Float) : Float64

  Returns a random Float64 which is greater than or equal to 0 and less than max.

• #rand(range : Range(Int, Int)) : Int

  Returns a random integer in the given range.

• #rand(range : Range(Float, Float)) : Float

  Returns a random Float in the given range.

• #rand : Float64

  Generates a random Float64 between 0 and 1.

• #random_bytes(n : Int = 16) : Bytes

  Generates a slice filled with n random bytes.

• #random_bytes(buf : Bytes) : Nil

  Fills a given slice with random bytes.

• #urlsafe_base64(n : Int = 16, padding = false) : String

  URL-safe variant of #base64.

Constructor Detail

Class Method Detail

Instance Method Detail

Random::Secure.base64(4) # => "fK1eYg=="

Random::Secure.hex    # => "05f100a1123f6bdbb427698ab664ff5f"
Random::Secure.hex(1) # => "1a"

Random.new.next_bool # => true

Random.new.rand(10)   # => 5
Random.new.rand(5000) # => 2243

Random.new.rand(3.5)    # => 2.88938
Random.new.rand(10.725) # => 7.70147

Random.new.rand(10..20)                 # => 14
Random.new.rand(Int64::MIN..Int64::MAX) # => -5297435808626736140

Random.new.rand(6.2..21.768) # => 15.2989

r = Random.new
r.rand # => 0.167595
r.rand # => 0.0372991

Random.new.random_bytes    # => [145, 255, 191, 133, 132, 139, 53, 136, 93, 238, 2, 37, 138, 244, 3, 216]
Random.new.random_bytes(4) # => [217, 118, 38, 196]

slice = Bytes.new(4) # => [0, 0, 0, 0]
Random.new.random_bytes(slice)
slice # => [217, 118, 38, 196]

Random::Secure.urlsafe_base64                    # => "MAD2bw8QaBdvITCveBNCrw"
Random::Secure.urlsafe_base64(8, padding: true)  # => "vvP1kcs841I="
Random::Secure.urlsafe_base64(16, padding: true) # => "og2aJrELDZWSdJfVGkxNKw=="