LaurentGomila/SFML — comment on commit 191730ac0d639cfdef8fae560cdbc7d7e8c67db1
File: include/SFML/Graphics/Texture.hpp line 499
By nitrix:

I found the answer on the internet.

In this case on a i386 processor, it uses 2 32-bit memory addresses to form a 64-bit number together. Addition/substraction is easy, you do it by parts, the only gotcha is taking the carry-over from the lower part to the higher part. For multiplication/division, it's harder (ie more instructions).

It's obviously slow, quite a bit slower than 32 bit arithmetic for multiplication, but if you need it, it's there for you. And when you upgrade to a 64-bit processor compiler, it gets automatically optimized to one instruction with the bigger word size.

Anyway, I just learned something here. Thanks!