Documentation

https://en.wikipedia.org/wiki/Lehmer_random_number_generator

Create a MCG

>>> make 20 04
MCG {m = 23, a = 11, x = 5}

>>> make 101_000_000 20240429
MCG {m = 101000023, a = 197265, x = 20240430}

Period of the MCG.

Period is usually a bit larger than asked for, we look for the next prime:

>>> let g = make 9 04
>>> period g
10

>>> take 22 (unfoldr (Just . next) g)
[4,7,3,1,0,5,2,6,8,9,4,7,3,1,0,5,2,6,8,9,4,7]

Generate next number.

Generate next numbers until one less than given bound is generated.

Replacing next with reject n effectively cuts the period to n:

>>> let g = make 9 04
>>> period g
10

>>> take 22 (unfoldr (Just . reject 9) g)
[4,7,3,1,0,5,2,6,8,4,7,3,1,0,5,2,6,8,4,7,3,1]

if n is close enough to actual period of MCG, the rejection ratio is very small.