Why do logicals (booleans) in R require 4 bytes?

Question

For a vector of logical values, why does R allocate 4 bytes, when a bit vector would consume 1 bit per entry? (See this question for examples.)

Now, I realize that

Answer 1

Without knowing R at all, I suspect for much the same reason as C does, because it's way faster to load a size equal to the processors native word size.

Loading a single bit would be slow, especially from a bitfield since you'd have to mask out the bits that do not apply to your particular query. With a whole word you can just load it in a registry and be done with it. Since the size difference usually is not a problem the default implementation is to use a word sized variable. If the user wants something else there is always the option to do the bit-shifting required manually.

Concerning packing, at least on some processors it will cause a fault to read from a non-aligned address. So while you might declare a structure with a single byte in it surrounded by two int the byte might be padded to be 4 bytes in size regardless. Again, I don't know anything about R in particular, but I suspect the behaviour might be the same for performance reasons.

Addressing a single byte in an array is quite more involved, say you have an array bitfield and want to address bit x in it, the code would be something like this:

bit b = (bitfield[x/8] >> (x % 8)) & 1

to obtain either 0 or 1 for the bit you requested. In comparison to the straightforward array addressing of from a boolean array obtaining value number x: bool a = array[x]