`~(-1 << 64)` is incorrect

[dearblue]

Finding the 1's complement of a negative integer in the range bigint results in a non-exact value that fluctuates.

% bin/mruby -e 'p 5.times.map { ~(-1 << 64) }'
[-34994079809, -34994079889, -34994079825, -34994079809, -34994079889]

Ruby values are listed for reference.

% ruby32 -e 'p 5.times.map { ~(-1 << 64) }'
[18446744073709551615, 18446744073709551615, 18446744073709551615, 18446744073709551615, 18446744073709551615, 18446744073709551615]