Problem with Mod command

This is confusing me a bit.

Try the code:

print 2^(7-0)

And you should get a value of 128.00000 (and so forth)


But if you try

b:Int = 0 Mod 8

Print 2^(7-b)

You get 127.99999997.

Why are these results different, and how can I get around it?