This is just a small datapack that adds a rng function.

Description:
This functions generates a random number by using only the game time, an offset value, and the range value that the player has to set (defaults to 1 if the range is none, 0 or negative)


Setting RNG range:
You can set the range value with : /scoreboard players set rng.range rng <range value> (the number generated can have all values from 0 to rng.range -1)


Generate a number:
To generate a number, execute the command /function rng:rng. The Number gets stored in the scoreboard rng.rng.