Rand functions which return a random value

Mojo
1

The various rand functions in Mojo’s current Random library currently all take a region of memory via an unsafe pointer as a parameter and fills it with random values, and thus are memory unsafe.

However, in other systems level programming languages such as C, C++, and Rust, the rand functions in the standard library or the rand crate are functions which return a single random value. Will Mojo implement similar rand functions as those in the other languages? Such rand functions will be memory safe since they do not involve unsafe pointers.

2

Looking at the source code for Mojo’s random library:

the random functions there seem to be wrappers of functions from the KGen compiler for Python, which themselves are wrappers of Fortran’s random functions.

That is, unlike C/C++/Rust there is currently no native random library implemented solely in the Mojo language.

3

This is a good question. The random module is one of the older ones and could use some modernization. We should at least probably take a Span instead of an UnsafePointer and length.

functions which return a single random value

If you look in that same module you linked, you can see the methods:

fn random_float64(min: Float64 = 0, max: Float64 = 1) -> Float64:
fn random_si64(min: Int64, max: Int64) -> Int64:
fn random_ui64(min: UInt64, max: UInt64) -> UInt64:

which all return a single value. If you want to truncate them, you can then cast the result, e.g:

UInt32(random_ui64(0, 5))
4

For me, all these functions don’t work as the linking seems broken. I get something like Unresolved extern function 'KGEN_CompilerRT_RandomSInt64

5

This doesn’t repro on my machine. Can you give us more information about your setup / hardware / operating system?

Also note you should be calling random.seed yourself otherwise you will always be using the default seed of 0.

6

Hey Lukas, Apologies for the confusion! I found out that it works just fine on our cluster, however when I use slurm, I get the error Unresolved extern function 'KGEN_CompilerRT_RandomSInt64 . I put #!/bin/bash -l at the start of my shell script that I submit to slurm, but that also dosn’t seem to work. Any pointers are welcome!

7

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