note 107475 added to function.str-rot13

I was reminded again of the desire for a generic str_rot function. Character manipulation loops in PHP are slow compared to their C counterparts, so here's a tuned version of the previous function I posted. It's 1.6 times as fast, mainly by avoiding chr() calls. <?php function str_rot($s, $n = 13) { static $letters = 'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ'; $n = (int)$n % 26; if (!$n) return $s; if ($n == 13) return str_rot13($s); for ($i = 0, $l = strlen($s); $i < $l; $i++) { $c = $s[$i]; if ($c >= 'a' && $c <= 'z') { $s[$i] = $letters[(ord($c) - 71 + $n) % 26]; } else if ($c >= 'A' && $c <= 'Z') { $s[$i] = $letters[(ord($c) - 39 + $n) % 26 + 26]; } } return $s; } ?> But using strtr() you can get something 10 times as fast as the above : <?php function str_rot($s, $n = 13) { static $letters = 'AaBbCcDdEeFfGgHhIiJjKkLlMmNnOoPpQqRrSsTtUuVvWwXxYyZz'; $n = (int)$n % 26; if (!$n) return $s; if ($n < 0) $n += 26; if ($n == 13) return str_rot13($s); $rep = substr($letters, $n * 2) . substr($letters, 0, $n * 2); return strtr($s, $letters, $rep); } ?> This technique is faster because PHP's strtr is implemented in C using a byte lookup table (it has O(m + n) complexity). However, PHP 6 will use Unicode, so I guess(?) strtr will then have to be implemented with a search for each character (O(m * n)). Using strtr might still be faster since it offloads the character manipulation to C rather than PHP, but I don't really know. Take your pick. Happy coding! (Benchmark code): <?php for ($k = 0; $k < 10; $k++) { $s = 'The quick brown fox jumps over the lazy dog.'; $t = microtime(1); for ($i = 0; $i < 1000; $i++) $s = str_rot($s, $i); $t = microtime(1) - $t; echo number_format($t, 3) . "\n"; } ?> ---- Server IP: 212.126.36.70 Probable Submitter: 109.255.178.6 ---- Manual Page -- http://www.php.net/manual/en/function.str-rot13.php Edit -- https://master.php.net/note/edit/107475 Del: integrated -- https://master.php.net/note/delete/107475/integrated Del: useless -- https://master.php.net/note/delete/107475/useless Del: bad code -- https://master.php.net/note/delete/107475/bad+code Del: spam -- https://master.php.net/note/delete/107475/spam Del: non-english -- https://master.php.net/note/delete/107475/non-english Del: in docs -- https://master.php.net/note/delete/107475/in+docs Del: other reasons-- https://master.php.net/note/delete/107475 Reject -- https://master.php.net/note/reject/107475 Search -- https://master.php.net/manage/user-notes.php