PHP实现把数字ID转字母ID_php技巧

ID是网站中经常出现的，它一般是数字，但是我们发现现在的网站很多ID都是字母了,比如YouTube的视频播放页它的URL类似/watch?v=yzNjIBEdyww。 下面是一个生成字母ID的方法。
使用示例：

   alphaID(12354）；  //会将数字转换为字母。<BR>   alphaID('PpQXn7COf',true）；//会将字母ID转换为对应的数字。<BR>   alphaID(12354,false,6）；//指定生成字母ID的长度为6.<BR>

源码：

<?php<BR>/**<BR> * Translates a number to a short alhanumeric version<BR> *<BR> * Translated any number up to 9007199254740992<BR> * to a shorter version in letters e.g.:<BR> * 9007199254740989 --> PpQXn7COf<BR> *<BR> * specifiying the second argument true, it will<BR> * translate back e.g.:<BR> * PpQXn7COf --> 9007199254740989<BR> *<BR> * this function is based on any2dec && dec2any by<BR> * fragmer[at]mail[dot]ru<BR> * see: http://nl3.php.net/manual/en/function.base-convert.php#52450<BR> *<BR> * If you want the alphaID to be at least 3 letter long, use the<BR> * $pad_up = 3 argument<BR> *<BR> * In most cases this is better than totally random ID generators<BR> * because this can easily avoid duplicate ID's.<BR> * For example if you correlate the alpha ID to an auto incrementing ID<BR> * in your database, you're done.<BR> *<BR> * The reverse is done because it makes it slightly more cryptic,<BR> * but it also makes it easier to spread lots of IDs in different<BR> * d<strong>+本文来源gao@daima#com搞(%代@#码网</strong><pre>搞代gaodaima码

irectories on your filesystem. Example:
* $part1 = substr($alpha_id,0,1);
* $part2 = substr($alpha_id,1,1);
* $part3 = substr($alpha_id,2,strlen($alpha_id));
* $destindir = “/”.$part1.”/”.$part2.”/”.$part3;
* // by reversing, directories are more evenly spread out. The
* // first 26 directories already occupy 26 main levels
*
* more info on limitation:
* – http://blade.nagaokaut.ac.jp/cgi-bin/scat.rb/ruby/ruby-talk/165372
*
* if you really need this for bigger numbers you probably have to look
* at things like: http://theserverpages.com/php/manual/en/ref.bc.php
* or: http://theserverpages.com/php/manual/en/ref.gmp.php
* but I haven’t really dugg into this. If you have more info on those
* matters feel free to leave a comment.
*
* @author Kevin van Zonneveld
* @author Simon Franz
* @author Deadfish
* @copyright 2008 Kevin van Zonneveld (http://kevin.vanzonneveld.net)
* @license http://www.opensource.org/licenses/bsd-license.php New BSD Licence
* @version SVN: Release: $Id: alphaID.inc.php 344 2009-06-10 17:43:59Z kevin $
* @link http://kevin.vanzonneveld.net/
*
* @param mixed $in String or long input to translate
* @param boolean $to_num Reverses translation when true
* @param mixed $pad_up Number or boolean padds the result up to a specified length
* @param string $passKey Supplying a password makes it harder to calculate the original ID
*
* @return mixed string or long
*/
function alphaID($in, $to_num = false, $pad_up = false, $passKey = null)
{
$index = “abcdefghijklmnopqrstuvwxyz0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ”;
if ($passKey !== null) {
// Although this function’s purpose is to just make the
// ID short – and not so much secure,
// with this patch by Simon Franz (http://blog.snaky.org/)
// you can optionally supply a password to make it harder
// to calculate the corresponding numeric ID

for ($n = 0; $n<strlen($index); $n++) {
$i[] = substr( $index,$n ,1);
}

$passhash = hash(‘sha256’,$passKey);
$passhash = (strlen($passhash) < strlen($index))
? hash(‘sha512’,$passKey)
: $passhash;

for ($n=0; $n < strlen($index); $n++) {
$p[] = substr($passhash, $n ,1);
}

array_multisort($p, SORT_DESC, $i);
$index = implode($i);
}

$base = strlen($index);

if ($to_num) {
// Digital number <<– alphabet letter code
$in = strrev($in);
$out = 0;
$len = strlen($in) – 1;
for ($t = 0; $t <= $len; $t++) {
$bcpow = bcpow($base, $len – $t);
$out = $out + strpos($index, substr($in, $t, 1)) * $bcpow;
}

if (is_numeric($pad_up)) {
$pad_up–;
if ($pad_up > 0) {
$out -= pow($base, $pad_up);
}
}
$out = sprintf(‘%F’, $out);
$out = substr($out, 0, strpos($out, ‘.’));
} else {
// Digital number –>> alphabet letter code
if (is_numeric($pad_up)) {
$pad_up–;
if ($pad_up > 0) {
$in += pow($base, $pad_up);
}
}

$out = “”;
for ($t = floor(log($in, $base)); $t >= 0; $t–) {
$bcp = bcpow($base, $t);
$a = floor($in / $bcp) % $base;
$out = $out . substr($index, $a, 1);
$in = $in – ($a * $bcp);
}
$out = strrev($out); // reverse
}

return $out;
}

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