This is of course not a new invention. The earliest instance I could find with a bit of searching was from 2004, with Andrew Morton mentioning in it a code review so casually that it seems to have been a well established trick. But the vast majority of implementations I looked at do not do this.
So here’s the question: Why do people use the version that’s inferior and more complicated? I’ve must have written a dozen ring buffers over the years, and before being forced to really think about it, I’d always just used the first definition. I can understand why a textbook wouldn’t take advantage of unsigned integer wraparound. But it seems like it should be exactly the kind of cleverness that hackers would relish using and passing on.
Check out the comments for more information, a bit of code golf, and multiple links on tying shoelaces.