--- name: "Random" section: "3o" platform: "linux" package: "ocaml" version: "5.5.0-1" release: "Arch Linux 2026-11-01" platforms: ["linux"] url: "https://new.carta.tech/Random" --- # Random(3o) Pseudo-random number generators (PRNG). ## 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 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 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). 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