Basic checks against count-leading/trailing zeroes should be optimized

[Validark]

Here are some basic transformations applicable on architectures lacking fast clz/ctz instructions: Godbolt link

const T = u64;

export fn isCountLeadingZeroesEven1(x: T) bool {
    return 1 == @clz(x) & 1;
}

export fn isCountLeadingZeroesEven2(x: T) bool {
    const odd_bits: @TypeOf(x) =
@bitCast(@as(@Vector(@divExact(@bitSizeOf(@TypeOf(x)), 8), u8), @splat(0xaa)));
    return (x & ~odd_bits) > (x & odd_bits);
}

The previous code [1, 2] is actually useful for Atkinson et al.'s 1986 Min-Max Heap for telling whether a layer is a min layer or max layer. Here is an analogous transformation for count-trailing zeroes:

const T = u64;

export fn isCountTrailingZeroesEven1(x: u64) bool {
    return 1 == @ctz(x) & 1;
}

export fn isCountTrailingZeroesEven2(x: u64) bool {
    const odd_bits: @TypeOf(x) =
@bitCast(@as(@Vector(@divExact(@bitSizeOf(@TypeOf(x)), 8), u8), @splat(0xaa)));
    return ((x & (~x +% 1)) & odd_bits) != 0;
}