# Module Stdlib.Random

    module Random: Random

## Basic functions

    val init : int -> unit

Initialize the domain-local generator, using the argument as a seed. The same seed will always yield the same sequence of numbers.

    val full_init : int array -> unit

Same as `Random.init` but takes more data as seed.

    val self_init : unit -> unit

Initialize the domain-local generator with a random seed chosen in a system-dependent way. If a cryptographically secure pseudorandom number generator is available on the host machine, it is used to provide a highly random initial seed. Otherwise, a less random seed is computed from system parameters (current time, process IDs, domain-local state).

    val bits : unit -> int

Return 30 random bits in a nonnegative integer.

    val int : int -> int

`Random.int bound` returns a random integer between 0 (inclusive) and `bound` (exclusive). `bound` must be greater than 0 and less than 230.

- Raises `Invalid_argument` if `bound` <= 0 or `bound` >= 230.

    val full_int : int -> int

`Random.full_int bound` returns a random integer between 0 (inclusive) and `bound` (exclusive). `bound` may be any positive integer.

If `bound` is less than 231, then `Random.full_int bound` yields identical output across systems with varying `int` sizes.

If `bound` is less than 230, then `Random.full_int bound` is equal to `Random.int` `bound`.

If `bound` is at least 230 (on 64-bit systems, or non-standard environments such as JavaScript), then `Random.full_int` returns a value whereas `Random.int` raises `Invalid_argument`.

- Since 4.13
- Raises `Invalid_argument` if `bound` <= 0.

    val int_in_range : min:int -> max:int -> int

`Random.int_in_range ~min ~max` returns a random integer between `min` (inclusive) and `max` (inclusive). Both `min` and `max` are allowed to be negative; `min` must be less than or equal to `max`.

If both bounds fit in 32-bit signed integers (that is, if -231 <= `min` and `max` < 231), then `int_in_range` yields identical output across systems with varying `int` sizes.

- Since 5.2
- Raises `Invalid_argument` if `min > max`.

    val int32 : Int32.t -> Int32.t

`Random.int32 bound` returns a random integer between 0 (inclusive) and `bound` (exclusive). `bound` must be greater than 0.

- Raises `Invalid_argument` if `bound` <= 0.

    val int32_in_range : min:int32 -> max:int32 -> int32

`Random.int32_in_range ~min ~max` returns a random integer between `min` (inclusive) and `max` (inclusive). Both `min` and `max` are allowed to be negative; `min` must be less than or equal to `max`.

- Since 5.2
- Raises `Invalid_argument` if `min > max`.

    val nativeint : Nativeint.t -> Nativeint.t

`Random.nativeint bound` returns a random integer between 0 (inclusive) and `bound` (exclusive). `bound` must be greater than 0.

- Raises `Invalid_argument` if `bound` <= 0.

    val nativeint_in_range : min:nativeint -> max:nativeint -> nativeint

`Random.nativeint_in_range ~min ~max` returns a random integer between `min` (inclusive) and `max` (inclusive). Both `min` and `max` are allowed to be negative; `min` must be less than or equal to `max`.

- Since 5.2
- Raises `Invalid_argument` if `min > max`.

    val int64 : Int64.t -> Int64.t

`Random.int64 bound` returns a random integer between 0 (inclusive) and `bound` (exclusive). `bound` must be greater than 0.

- Raises `Invalid_argument` if `bound` <= 0.

    val int64_in_range : min:int64 -> max:int64 -> int64

`Random.int64_in_range ~min ~max` returns a random integer between `min` (inclusive) and `max` (inclusive). Both `min` and `max` are allowed to be negative; `min` must be less than or equal to `max`.

- Since 5.2
- Raises `Invalid_argument` if `min > max`.

    val float : float -> float

`Random.float bound` returns a random floating-point number between 0 and `bound` (inclusive). If `bound` is negative, the result is negative or zero. If `bound` is 0, the result is 0.

    val bool : unit -> bool

`Random.bool ()` returns `true` or `false` with probability 0.5 each.

    val bits32 : unit -> Int32.t

`Random.bits32 ()` returns 32 random bits as an integer between `Int32.min_int` and `Int32.max_int`.

- Since 4.14

    val bits64 : unit -> Int64.t

`Random.bits64 ()` returns 64 random bits as an integer between `Int64.min_int` and `Int64.max_int`.

- Since 4.14

    val nativebits : unit -> Nativeint.t

`Random.nativebits ()` returns 32 or 64 random bits (depending on the bit width of the platform) as an integer between `Nativeint.min_int` and `Nativeint.max_int`.

- Since 4.14

## Advanced functions

The functions from module `Random.State` manipulate the current state of the random generator explicitly. This allows using one or several deterministic PRNGs, even in a multi-threaded program, without interference from other parts of the program.

    module State: sig .. end

    val get_state : unit -> State.t

`get_state()` returns a fresh copy of the current state of the domain-local generator (which is used by the basic functions).

The current state is unchanged, which means that random numbers generated from multiple calls to `get_state ()` will be identical.

See `Random.State.make_self_init` and `Random.split` instead to obtain a fresh state that is not shared.

    val set_state : State.t -> unit

`set_state s` updates the current state of the domain-local generator (which is used by the basic functions) by copying the state `s` into it.

    val split : unit -> State.t

Draw a fresh PRNG state from the current state of the domain-local generator used by the default functions. (The state of the domain-local generator is modified.) See `Random.State.split`.

- Since 5.0