re output space
or more available input, which it will be in this code.
<pre><b>
            ret = deflate(&amp;strm, flush);    /* no bad return value */
            assert(ret != Z_STREAM_ERROR);  /* state not clobbered */
</b></pre>
Now we compute how much output <tt>deflate()</tt> provided on the last call, which is the
difference between how much space was provided before the call, and how much output space
is still available after the call.  Then that data, if any, is written to the output file.
We ca