How to check native support of @mulAdd at compile time?

[expikr]

I'm implementing this algorithm over here and there are two variants: one for hardware with fused mulAdd instructions and another for those without.

What's the idiomatic way of choosing which code path to dispatch given a compile target?

[nektro]

@mulAdd will always be available. if the target does not have it then a software implementation will be provided from compiler_rt

you can also manually do the cpu feature set detection like in what std.crypto does.
eg https://github.com/ziglang/zig/blob/master/lib/std/crypto/sha2.zig#L203
feature lists are in the arch files in https://github.com/ziglang/zig/tree/master/lib/std/Target/