Question

I have a small piece of code that requires to read 4-bit values bitpacked in a 32-bit integer. Since I need to call this operation several times, even if it’s simple, I require max speed on it.
I was pondering about macros and inline functions, thus I made this macro:

#define UI32TO4(x, p) (x >> ((p - 1) *4) & 15)

And I have an inline function that does the same thing.

static inline Uint8 foo_getval(Uint32 bits, int pos){
    return (bits >> ((pos-1)*4)) & 15;
}

Considering the simplicity of the operation, and that the values are already prepared for this call (so no possibility of calling on the wrong types, or pass values that are too big or that stuff), what would be the best one to use? Or, at least, the most comprehensible for someone else potentially reading/modifying the code later on?

EDIT! Forgot to mention, I am using C99.

Answer 1

The function is safer. Your assumptions that the values are always “right” only holds while you’re developing that code. You can’t tell if someone down the line (or yourself when you’re tired) won’t pass unexpected values.

The compiler will do the inlining when it sees it as effective. Use type-safe functions whenever you can, use macros only when you have no other practical choice.