Maybe. Inlining small functions can reduce cache load, and it means no call/ret instructions and no overhead of argument passing. Moreover inlining allows futher optimizations which can't be done without breaking function boundaries. It may be noticeable. And may be not. Depends on loop.
> what's the best practice for inlining a computation like this?
There are a lot of examples can be seen in linux kernel. Just random example from include/linux/list.h:
static inline void list_replace(struct list_head *old,
struct list_head *new)
{
new->next = old->next;
new->next->prev = new;
new->prev = old->prev;
new->prev->next = new;
}
With C++ such a functions will be a methods in most cases, and (if so) "static" would be unneeded and wrong.
And you'll need to turn on optimizations when compiling. Compiler is not inlining when not optimizing.
If you want you can nudge the compiler in the direction you want via the "inline" keyword, although the compiler won't always take this suggestion to heart. MSVC has "__forceinline" but it too will not always comply.
Before the "inline" keyword, macros were the standard way to do this, IIRC