sigset_bit_index

fn sigset_bit_index(sig: usize) struct { word: usize, mask: SigsetElement } {
    assert(sig > 0);
    assert(sig < NSIG);
    const bit = sig - 1;
    return .{
        .word = bit / @bitSizeOf(SigsetElement),
        .mask = @as(SigsetElement, 1) << @truncate(bit % @bitSizeOf(SigsetElement)),
    };
}