Thanks @SolitudeSF!
Here are my results for i7-970 hexa-core @ 3.2 GHz. Nim 0.18.1 (devel), GCC
7.3.1, Linux kernel 4.9
10_000_000_000 0.544 secs
50_000_000_000 2.954 secs
100_000_000_000 5.513 secs
500_000_000_000 73.863 secs
1_000_000_000_000 153.260 secs
2_000_000_000_000 334.612 secs
3_000_000_000_000 763.395 secs
