 of
            <em class="parameter"><code>mem</code></em>. The content of <em class="parameter"><code>data</code></em> is written into <em class="parameter"><code>mem</code></em> and the original contents of <em class="parameter"><code>mem</code></em>
            are returned. The contents of the memory being updated by the atomic operation are
            guaranteed not to be modified by any other assignment or atomic memory function in any shader
            invocation between the time the original valu