A library to generate random numbers for cryptographic applications in OCaml. It relies on the rand Rust library.

You'll need Rust: https://rustup.rs/

Then:

$ opam install randoml

Or if you have esy:

{
    "dependencies": {
+        "@opam/randoml": "*"
    },
}

Fill a buffer with random bytes:

let buf = Bytes.create 16 in
rand_fill buf

Get a random int32:

let x = rand_int32 ()

Get a random int64:

let x = rand_int64 ()

Get a random int32 between 1 and 100000000:

let lower = Int32.of_int_exn 1 in
let upper = Int32.of_int_exn 100000000 in
let x = rand_int32_range lower upper

Get a random int64 between 1 and 100000000:

let lower = Int64.of_int_exn 1 in
let upper = Int64.of_int_exn 100000000 in
let x = rand_int64_range lower upper

Get a random Bigint upperbounded by some number (warning: it won't work well if your upperbound is not smaller and close to a power of 2):

let upperbound =
Bigint.of_string
    "7067388259113537318333190002971674063309935587502475832486424805170478604"
in
let x = rand_bigint upperbound

As opam installs dependencies in a sandbox, rust dependencies need to be vendored via cargo vendor. Thus, this command needs to be executed every time there's a change in the Cargo.lock file.