Speed of unpack() in PHP
I needed to extract a list of integers from a binary string. I was curious to know if PHP’s unpack function is fast compared to a custom function, so I wrote a test for it.
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<?php$filename = '<some large file>';$unpack_time = 0.0;$unpack_time2 = 0.0;$unpack_custom_time = 0.0;$fp = fopen($filename, 'rb');while (!feof($fp)) { $content = fread($fp, 1048576); $start = microtime(true); $array = unpack('N*', $content); $stop = microtime(true); $unpack_time += ($stop - $start); $start = microtime(true); $array = unpack('V*', $content); $stop = microtime(true); $unpack_time2 += ($stop - $start); $start = microtime(true); $array = unpack_custom($content); $stop = microtime(true); $unpack_custom_time += ($stop - $start);}fclose($fp);print "\$unpack_time = $unpack_time\n";print "\$unpack_time2 = $unpack_time2\n";print "\$unpack_custom_time = $unpack_custom_time\n";function unpack_custom($content) { $len = strlen($content); $result = array(); for ($i = 0; $i + 3 < $len; $i += 4) { $result[] = (ord($content[$i]) << 24) + (ord($content[$i + 1]) << 16) + (ord($content[$i + 2]) << 8) + ord($content[$i + 3]); } return $result;}?>The printout: (The numbers are the number of seconds needed to convert the file’s content into integers. The file I used was 2.67 MB in size.)
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$unpack_time = 1.34654474258$unpack_time2 = 1.44259476662$unpack_custom_time = 127.910765171The result matches my earlier experiment, from which I have learned that custom functions are much slower than PHP’s built-in ones. Whenever possible, use the latter. By do that, you also have less code to write and debug.