How to efficiently convert a few bytes into an integer between a range?

Question

I\'m writing something that reads bytes (just a List) from a remote random number generation source that is extremely slow. For that and my personal

Answer 1

range 1 to r
256^a >= r

first find 'a' 

get 'a' number of bytes into array A[]

num=0
for i=0 to len(A)-1
    num+=(A[i]^(8*i))
next

random number = num mod range