It appears that the ULong modulus operator is broken. If we run this code:

    for (i <- 0 to 16 ) {

      val numerator = ULong(i)

      val denominator = ULong(8)

      val remainder = numerator % denominator

      println(i + " % 8 = " + remainder)

    }

we get the result:

0 % 8 = 0

1 % 8 = 1

2 % 8 = 2

3 % 8 = 3

4 % 8 = 4

5 % 8 = 5

6 % 8 = 6

7 % 8 = 7

8 % 8 = 8

9 % 8 = 9

10 % 8 = 10

11 % 8 = 11

12 % 8 = 12

13 % 8 = 13

14 % 8 = 14

15 % 8 = 15

16 % 8 = 0

Anything % 8 should always be less than 8. But some results are greater than 8. Not sure exactly what is going on, and the generated bytecode is really hard to follow. In fact, I wouldn't be surprised if ULongs are actually slowing things down. The byte code was kindof a mess. We might want to revisit ULongs and how else to support > 4GB files.