Which is more efficient: Bit, byte or int?

Question

Let's say that you were to have a structure similar to the following:

struct Person {
  int  gender;         // betwwen 0-1
  int  age;            // between 0-200
  int  birthmonth;     // between 0-11
  int  birthday;       // between 1-31
  int  birthdayofweek; // between 0-6
}

In terms of performance, which would be the best data type to store each of the fields? (e.g. bitfield, int, char, etc.)

It will be used on an x86 processor and stored entirely in RAM. A fairly large number will need to be stored (50,000+), so processor caches and such will need to be taken into account.

Edit: OK, let me rephrase the question. If memory usage is not important, and the entire dataset will not fit into the cache no matter which datatypes are used, is it generally better to use smaller datatypes to fit more of the data into the CPU cache, or is it better to use larger datatypes to allow the CPU to perform faster operations? I am asking this for reference only, so code readability and such should not be considered.

Answer 1

1. Don't worry about it; use what is semantically correct, and most readable
2. There is no answer that is correct all the time. It depends on the platform and compiler. If you really care, then you have to test.

In general, I would stay stick with ints... except for gender which should probably be an enum.