對于想隱藏真實id的需求，比如想加密userId等
使用示例：

	 * 不指定長度* AlphaIDCustom(12354）；  //會將數(shù)字轉換為字母。* AlphaIDCustom('PpQXn7COf',true）；//會將字母ID轉換為對應的數(shù)字。* 指定長度* AlphaIDCustom(123456,false,6）；//指定生成字母ID的長度為6.* AlphaIDCustom('xyMSSI',ture,6）；//會將字母ID轉換為對應的數(shù)字.

源碼：

    /*** 數(shù)字ID和字符串ID互相轉換* 如：* 不指定長度* AlphaIDCustom(12354）；  //會將數(shù)字轉換為字母。* AlphaIDCustom('PpQXn7COf',true）；//會將字母ID轉換為對應的數(shù)字。* 指定長度* AlphaIDCustom(123465,false,6）；//指定生成字母ID的長度為6.* AlphaIDCustom('xyMSSI',ture,6）；//會將字母ID轉換為對應的數(shù)字.* @param $in* @param false $to_num 是否轉成數(shù)字* @param false $pad_up 長度限制* @param null $passKey 加密* @return false|string*/function AlphaIDCustom($in, $to_num = false, $pad_up = false, $passKey = null){
//        $index = "abcdefghijklmnopqrstuvwxyz0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ";//亂序$index = 'SITEQZFyWtpPjRxVYc7uL094bOA8rDCBMmgki23XJnsfHd5oqNwzhUlGKave61';if ($passKey !== null) {for ($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 codeif (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;}