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const std = @import("std");

fn expand8xu8To16xu4AsByteVector(vec: @Vector(8, u8)) @Vector(16, u8) {
    return std.simd.interlace(.{ vec & @as(@Vector(8, u8), @splat(0xF)), vec >> @splat(4) });
}

fn sel(vec: anytype) @Vector(@typeInfo(@TypeOf(vec)).vector.len, u8) {
    const false_vec: @Vector(16, u8) = @splat(0);
    const true_vec = ~false_vec;
    return @select(u8, vec, true_vec, false_vec);
}

fn bsl2(vec1: anytype, vec2: @TypeOf(vec1), vec3: @TypeOf(vec1)) @TypeOf(vec1) {
    return (vec1 & (vec2 ^ vec3)) ^ vec3;
}

fn bsl(vec1: anytype, vec2: @TypeOf(vec1), vec3: @TypeOf(vec1)) @TypeOf(vec1) {
    return (vec1 & vec2) | (~vec1 & vec3);
}

export fn bad_bsl(x: u64, buffer1_half1: @Vector(16, u8), buffer1_half2: @Vector(16, u8), buffer2_half1: @Vector(16, u8), buffer2_half2: @Vector(16, u8)) @Vector(32, u8) {
    const splatted = blk: {
        // try to avoid https://github.com/llvm/llvm-project/issues/92211
        var y: u64 = x; // spread out each bit of `x` into a nibble of `y`
        // zig fmt: off
        // start positions:   0b0000000000000000000000000000000000000000000000001111111111111111;
        y = (y | (y << 24)); //  & 0b0000000000000000000000001111111100000000000000000000000011111111 this AND is optimized out
        y = (y | (y << 12)) & 0b0000000000001111000000000000111100000000000011110000000000001111;
        y = (y | (y <<  6)); //  & 0b0000001100000011000000110000001100000011000000110000001100000011 this AND is optimized out
        y = (y | (y <<  3)) & 0b0001000100010001000100010001000100010001000100010001000100010001;
        // zig fmt: on
        break :blk y;
    };

const selector_compressed = sel(expand8xu8To16xu4AsByteVector(@bitCast(splatted)) != @as(@Vector(16, u8), @splat(0)));
    const selectors: [2]@Vector(16, u8) = @bitCast(std.simd.interlace(.{ selector_compressed, selector_compressed }));

return @bitCast([2]@Vector(16, u8){
        bsl(
            selectors[0],
            buffer1_half1,
            buffer2_half1,
        ),
        bsl(
            selectors[1],
            buffer1_half2,
            buffer2_half2,
        ),
    });
}