Running your code under Perl 6 displays the following output for the last line:

x1=256080, x2=258160, diff=2080
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And you can even compare $diff with 2080:

say $diff == 2080;   # -> True
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The reason for the difference is that Perl 6 is not using floats for such calculations, but rationals, so that 4/25 is not stored internally as 0.16, but as 4/25, i.e. a numerator and a denominator.