I found that types like uint32_least_t to be much less useful after learning that standard C/C++ types already have these guarantees. Namely: char is at least 8 bits wide, short is at least 16 bits wide, int is at least 16 bits wide, long is at least 32 bits wide, long long is at least 64 bits wide.

Implementing cryptographic algorithms using uint32_least_t can be dangerous. Suppose that short is 32 bits wide and int is 48 bits wide. Your uint32_least_t might be mapped to unsigned short. When you do something like (x << 31), x gets promoted to signed int, and then you might be shifting a 1 into the sign bit, which is undefined behavior. So I would say that a better idea is to use unsigned long, which is guaranteed not to promote to a higher-rank type.