Nice function. I did it the other way round:

function uncompress($srcName, $dstName) {
   $zp = gzopen($srcName, "r");
   while(!gzeof($zp))
        $string .= gzread($zp, 4096);
   gzclose($zp);

   $fp = fopen($dstName, "w");
   fwrite($fp, $string, strlen($string));
   fclose($fp);
}

uncompress("./myfile.txt.gz", "./myfile.txt");

A shorter approach would be:

function uncompress($srcName, $dstName) {
  $string = implode("", gzfile($srcName));
  $fp = fopen($dstName, "w");
  fwrite($fp, $string, strlen($string));
  fclose($fp);
}