Comment by pklausler

6 months ago

Easy to count leading zeroes in a branch-free manner without a hardware instruction using a conditional move and a de Bruijn sequence; see https://github.com/llvm/llvm-project/blob/main/flang/include... .

3 comments

pklausler

    x |= x >> 1;
    x |= x >> 2;
    x |= x >> 4;
    x |= x >> 8;
    x |= x >> 16;
    x |= x >> 32;

Isn't there another way to do this without so many data races?

I feel like this should be

   x |= x >> 1 | x >> ??? ...

gpderetta 6 months ago
By data races I assume you actually mean data dependencies?
- hinkley 6 months ago
  
  Oops. Yes.