pklausler • 8 hours 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... .

1
hinkley • 5 hours ago 

    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 >> ??? ...

1 reply
gpderetta • 5 hours ago

By data races I assume you actually mean data dependencies?