uniform half4 colorGreen, colorRed;

half4 main(float2) {
    bool ok = true;

    // Unary bitwise negation '~' (scalar):
    uint val = uint(colorGreen.r);  // 0
    uint2 mask = uint2(val, ~val);

    // Unary bitwise negation '~' (vector, uint):
    int2 imask = int2(~mask);

    // Unary bitwise negation '~' (vector, int):
    mask = ~mask & uint2(~imask);
    ok = ok && (mask == uint2(0));

    return ok ? colorGreen : colorRed;
}