well according to the post i tried the following:

//echo -a $calc(10000000000000000000000 + 0)
it returns 10000000000000000000000
which is perfectly fine.

but when i try to add another 0 behind
//echo -a $calc(100000000000000000000000 + 0)
it returns 99999999999999992000000

seems like the problems only affect with int numbers bigger than 24char