Random(3) OCaml library Random(3) NAME Random - Pseudo-random number generators (PRNG). Module Module Random Documentation Module Random : sig end Pseudo-random number generators (PRNG). With multiple domains, each domain has its own generator that evolves independently of the generators of other domains. When a domain is created, its generator is initialized by splitting the state of the generator associated with the parent domain. In contrast, all threads within a domain share the same domain-local generator. Independent generators can be created with the Random.split function and used with the functions from the Random.State module. Before5.0 Random value generation used a different algorithm. This affects all the functions in this module which return random values. 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 /dev/urandom 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 2^30. Raises Invalid_argument if bound <= 0 or bound >= 2^30. 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 2^31, then Random.full_int bound yields identical output across systems with varying int sizes. If bound is less than 2^30, then Random.full_int bound is equal to Random.int bound . If bound is at least 2^30 (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 -2^31 <= min and max < 2^31), 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). 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 OCamldoc 2025-01-20 Random(3)