What is the most efficient way to represent small values in a struct?

Question

Often I find myself having to represent a structure that consists of very small values. For example, Foo has 4 values, a, b, c, d that, range from

Answer 1

You've stated the common and ambiguous C/C++ tag.

Assuming C++, make the data private and add getters/ setters. No, that will not cause a performance hit - providing the optimizer is turned on.

You can then change the implementation to use the alternatives without any change to your calling code - and therefore more easily finesse the implementation based on the results of the bench tests.

For the record, I'd expect the struct with bit fields as per @dbush to be most likely the fastest given your description.

Note all this is around keeping the data in cache - you may also want to see if the design of the calling algorithm can help with that.