24 ms·

You can't always do those things. Yes, pointer length is almost always faster. But it's not always faster. https://lemire.me/blog/2020/09/03/sentinels-can-be-

• yakubin 3y ago
  You can. Here is my version: <https://godbolt.org/z/91KecEfbM https://godbolt.org/z/91KecEfbM> Results: N = 10000 range 1218.1 sentinel 937.258 mine 672.227 ratio 1.29964 (ratio is range/sentinel, not mine/whatever) You can get even more crazy with SIMD. But for all that you need to know the length beforehand. Edit: The b4 variable should actually be called b8. That's a remnant of a previous version, where I used 32-bit chunks.
  • throwawaymaths 3y ago
    Read the blog post. Dan lemire isn't exactly a slouch.
    • GrumpySloth 3y ago
      I read it. I don't see your point. Sentinel values simply give you a very low performance ceiling that you can't optimise past. What I wrote only took me a couple minutes. It's far from optimal (but it already takes 2/3 the time the sentinel version takes, and 1/2 the time Lemire's range version takes). With thorough effort I bet you could get at least 10 times faster than that, provided you are given the length. With sentinels, you're just left with the original performance levels you can't improve.