What is the difference between intXX_t and int_fastXX_t?

Question

I have recently discovered existence of standard fastest type, mainly int_fast32_t and int_fast64_t.

I was always told that, for normal use on mainstream archit

Answer 1

Gnu libc defines {int,uint}_fast{16,32}_t as 64-bit when compiling for 64-bit CPUs and 32-bit otherwise. Operations on 64-bit integers are faster on Intel and AMD 64-bit x86 CPUs than the same operations on 32-bit integers.