I have always considered these "double ring" buffers. Along the same lines as how you figure out which race car is in the race is in lead by their position and lap count. You run your indexes in the range 0 .. (2 * SIZE) and then empty is
Basically you're full if you're at the same relative index and your on different laps, you are empty if you at the same relative index on the same lap. If you do this with power of 2 size then the 'lap' is just the bit 2 << SIZE.
No, I think the author is using the full range of a 32 bit int. So read could be any 32 bit integer, even if the size of the ring is 1.
(The trick is that SIZE has to be a power of two, or else when you increment from 2^32-1 to 0, your pointers will jump to a different position in the array.)
