Implementation of Knuth's bad random number generator from TAOCP Volume 2, Chapter 3

knuth.py

ten5  = 100000
ten8  = 100000000
ten9  = 1000000000
ten10 = 10000000000

def krng(x):
    iterations = x/ten9 + 1

    while iterations > 0:
        step = (x/ten8) % 10 + 3

        if step == 3:
            if x < 5000000000L:
                x += 5000000000L
            step += 1

        if step == 4:
            x = ((x*x)/ten5) % ten10
            step += 1

        if step == 5:
            x = (1001001001L*x) % ten10
            step += 1

        if step == 6:
            if x < ten8:
                x += 9814055677L
            else:
                x = ten10 - x
            step += 1

        if step == 7:
            x = ten5*(x % ten5) + (x/ten5)
            step += 1

        if step == 8:
            x = (1001001001L*x) % ten10
            step += 1

        if step == 9:
            s = 1
            t = x
            for i in range(10):
                if t % 10 > 0:
                    x -= s
                s *= 10
                t /= 10
            step += 1

        if step == 10:
            if x < ten5:
                x = x*x + 99999L
            else:
                x -= 99999L
            step += 1

        if step == 11:
            while x < ten9:
                x *= 10
            step += 1

        if step == 12:
            x = ((x*(x-1))/ten5) % ten10
            step += 1

        iterations -= 1

    return int(x)

print krng(6065038420L)