On: SIMD with Zig

[ayende]

A better option here would be to use `_mm_movemask_epi8`, for the vector:

``` { false, false, false, false, true, false, false, true } ```

It will give an int with the bits: `0b0000_1001`

You can then do `@clz` to get the index of the first set bit.

That would save you the `@reduce` and `@splat`. I don't see how to access move mask from Zig, however.

Note that the standard library has `std.zig.firstIndexOfValue`, which does what you have in the post, basically. And there is `std.zig.firstTrue`, which does the the same thing as `@clz` in this case, but I don't know what kind of assembly it will generate.

[e4m2 → ayende]

> I don't see how to access move mask from Zig, however.

Bools in a vector each only occupy one bit. You can @bitCast an N element bool vector directly to a uN integer and it will generate movemask on x86.

[anonymoushn → e4m2]

This must be new. Last year the compiler believed vectors of bools were both N bytes wide and N bits wide for different purposes and we ended up needing

  @ptrCast(*const u64, &my_bool_vec).*