Describing how a function generating random numbers does not give equal likelihood

So I created a really terrible function in which is made just to generate random numbers, I was given that RINT is a built-in function that generates any integer 0-255 INCLUSIVE.

BEGIN RanInt(Low, High, Result)  

tmpA = RINT

Range = High - Low + 1

tmpB = tmpA/256 * Range

tmpC = int(tmpB)

tmpD = tmpC + Low

Result = tmpD

END RanInt

Now, using my function, I have to analyse why this function will not generate each possible number with equal likelihood. Firstly, will I approach this question about the actual computer hardware? Or the fact that the possible chance of each number occuring in equal likelihood must be divisible by the range of numbers that can specified in the RanInt function? Thanks!!