This converts a framerule number and frame offsets to an RNG value compatible with SMB Practice Hack v3.0.
Please note that the frame offset notation is different to threecreepio's broken-fr notation because Pellsson's framerule implementation starts at 1, and Threecreepio's offset implementation starts at 1.
For example 636-6 on broken-fr would equate to 637-5 here.
Any framerules less than framerule 2 are not accepted in the formula as any values in RNG at that time are not present within the 32767 possible combinations during normal gameplay.
Rule+Offset to RNG formula by Simplistic6502