Fast Sorting, Branchless by Design
00f.net
00f.net
Are there plans to upstream this into the Zig std library? Seems like it could be useful for more than just the cryptography package, since the benchmarks at the end have it often being faster than std pdqsort. I just checked the issue trackers on Codeberg and GitHub, and didn't see anything mentioning djbsort or NTRU Prime, which leads me to believe there aren't (official) plans to upstream this (yet).
pdqsort is a generic comparison sort. Want to sort employee names, customer email addresses, JSON blobs, or Zebras? No problem, pdqsort just needs an ordering, in both Zig and C++ you write this as a single boolean "less" predicate.
DJB's speed-up relies on vectorization, which works great for integers or things you can squint at and see an integer - but obviously can't sort your employee names, customer email addresses, JSON blobs or Zebras. You could write these branchless network designs anyway but I'm pretty sure they'd be markedly slower, at least for some common inputs.
const diff = if (order == .asc) b_int - a_int else a_int - b_int;
const sign_bit: u1 = @truncate(@as(UWInt, @bitCast(diff)) >> @intCast(bits));
var mask_word = @as(usize, 0) -% @as(usize, sign_bit);
e.g.
0x8000_0000 < 0x0000_0001 for signed numbers
0x8000_0000 - 0x0000_0001 = 0x7fff_ffff, high bit clearDidn't see it mentioned in the article though, maybe I missed it. If not, I think that this detail would be a good thing to include, both since it's a common mistake that others with less experience might make, and to get ahead of nitpicky comments like mine :)