View Source random (stdlib v6.0)

Pseudo-random number generation.

This module provides a random number generator. The method is attributed to B.A. Wichmann and I.D. Hill in 'An efficient and portable pseudo-random number generator', Journal of Applied Statistics. AS183. 1982. Also Byte March 1987.

The algorithm is a modification of the version attributed to Richard A. O'Keefe in the standard Prolog library.

Every time a random number is requested, a state is used to calculate it, and a new state is produced. The state can either be implicit (kept in the process dictionary) or be an explicit argument and return value. In this implementation, the state (the type ran/0) consists of a tuple of three integers.

Note
This random number generator is not cryptographically strong. If a strong cryptographic random number generator is needed, use one of functions in the crypto module, for example, crypto:strong_rand_bytes/1.

Note
The improved rand module is to be used instead of this module.

Note

Some of the functions use the process dictionary variable random_seed to remember the current seed.

If a process calls uniform/0 or uniform/1 without setting a seed first, seed/0 is called automatically.

The implementation changed in Erlang/OTP R15. Upgrading to R15 breaks applications that expect a specific output for a specified seed. The output is still deterministic number series, but different compared to releases older than R15. Seed {0,0,0} does, for example, no longer produce a flawed series of only zeros.

Summary

Types

ran()

The state.

Functions

seed0() deprecated

Returns the default state.

seed() deprecated

Seeds random number generation with default (fixed) values in the process dictionary and returns the old state.

seed(SValue) deprecated

seed({A1, A2, A3}) is equivalent to seed(A1, A2, A3).

seed(A1, A2, A3) deprecated

Seeds random number generation with integer values in the process dictionary and returns the old state.

uniform() deprecated

Returns a random float uniformly distributed between 0.0 and 1.0, updating the state in the process dictionary.

uniform(N) deprecated

Returns, for a specified integer N >= 1, a random integer uniformly distributed between 1 and N, updating the state in the process dictionary.

uniform_s(State0) deprecated

Returns, for a specified state, a random float uniformly distributed between 0.0 and 1.0, and a new state.

uniform_s(N, State0) deprecated

Returns, for a specified integer N >= 1 and a state, a random integer uniformly distributed between 1 and N, and a new state.

Types

ran()

(not exported)

-type ran() :: {integer(), integer(), integer()}.

The state.

Functions

seed0()

This function is deprecated. random:seed0/0 is deprecated; use the 'rand' module instead.

-spec seed0() -> ran().

Returns the default state.

seed()

This function is deprecated. random:seed/0 is deprecated; use the 'rand' module instead.

-spec seed() -> ran().

Seeds random number generation with default (fixed) values in the process dictionary and returns the old state.

seed(SValue)

This function is deprecated. random:seed/1 is deprecated; use the 'rand' module instead.

-spec seed(SValue) -> undefined | ran()
        when SValue :: {A1, A2, A3} | integer(), A1 :: integer(), A2 :: integer(), A3 :: integer().

seed({A1, A2, A3}) is equivalent to seed(A1, A2, A3).

seed(A1, A2, A3)

This function is deprecated. random:seed/3 is deprecated; use the 'rand' module instead.

-spec seed(A1, A2, A3) -> undefined | ran() when A1 :: integer(), A2 :: integer(), A3 :: integer().

Seeds random number generation with integer values in the process dictionary and returns the old state.

The following is an easy way of obtaining a unique value to seed with:

random:seed(erlang:phash2([node()]),
            erlang:monotonic_time(),
            erlang:unique_integer())

For details, see erlang:phash2/1, erlang:node/0, erlang:monotonic_time/0, and erlang:unique_integer/0.

uniform()

This function is deprecated. random:uniform/0 is deprecated; use the 'rand' module instead.

-spec uniform() -> float().

Returns a random float uniformly distributed between 0.0 and 1.0, updating the state in the process dictionary.

uniform(N)

This function is deprecated. random:uniform/1 is deprecated; use the 'rand' module instead.

-spec uniform(N) -> pos_integer() when N :: pos_integer().

Returns, for a specified integer N >= 1, a random integer uniformly distributed between 1 and N, updating the state in the process dictionary.

uniform_s(State0)

This function is deprecated. random:uniform_s/1 is deprecated; use the 'rand' module instead.

-spec uniform_s(State0) -> {float(), State1} when State0 :: ran(), State1 :: ran().

Returns, for a specified state, a random float uniformly distributed between 0.0 and 1.0, and a new state.

uniform_s(N, State0)

This function is deprecated. random:uniform_s/2 is deprecated; use the 'rand' module instead.

-spec uniform_s(N, State0) -> {integer(), State1}
             when N :: pos_integer(), State0 :: ran(), State1 :: ran().

Returns, for a specified integer N >= 1 and a state, a random integer uniformly distributed between 1 and N, and a new state.