Is Swift really slow at dealing with numbers?

Here are optimization levels for the Swift compiler's code generation (you can find them in Build Settings):

[-Onone] no optimizations, the default for debug.[-O]     perform optimizations, the default for release.[-Ofast] perform optimizations and disable runtime overflow checks and runtime type checks.

Using your code I got these times at different levels of optimization:

[-Onone]

Swift: 6110.98903417587msObjc:  134.006023406982ms

[-O]

Swift: 89.8249745368958msObjc:  85.5680108070374ms

[-Ofast]

Swift: 77.1470069885254msObjc:  76.3399600982666ms

Keep in mind that -Ofast is comes with risks. e.g. It will silently ignore integer and array overflows, producing nonsense results, so if you choose to use it you'll have to guarantee yourself that overflows aren't possible in your program.

Credits to @sjeohp for his comment which is basically the answer to the question.

I tried optimizing the code to the most aggressive way in Release for both LLVM and Swift optimizations:

Compiled the project in Release and got:

[1040101022027, 1040101022039, 1040101022057, 1040101022099, 1040101022153] took: 63.211977481842ms[1040101022027, 1040101022039, 1040101022057, 1040101022099, 1040101022153] took: 60.0320100784302ms

Again, thanks @sjeohp for catching this !