生成原理
将10进制数字转换为[0-9A-Z]的36位进制字符。为了减少输入邀请码的歧义，我们将“0”和“O”去除，变成10进制转34进制；为了增加解密难度防止被猜到，我们将字符打乱；不足4位的，用0补充。
注意：$source_string字符顺序要一样，不然无法解密
加密
//生成邀请码
function createCode ($user_id)
{
static $source_string = 'E5FCDG3HQA4B1NPIJ2RSTUV67MWX89KLYZ';
$num = $user_id;
$code = '';
while ($num > 0) {
$mod = $num % 34;
$num = ($num - $mod) / 34;
$code = $source_string[$mod].$code;
}
if(empty($code[3])){
$code = str_pad($code, 4, '0', STR_PAD_LEFT);
}
return $code;
}解密
//解析邀请码
function deCode ($code)
{
static $source_string = 'E5FCDG3HQA4B1NOPIJ2RSTUV67MWX89KLYZ';
if (strrpos($code, '0') !== false){
$code = substr($code, strrpos($code, '0')+1);
}
$len = strlen($code);
$code = strrev($code);
$num = 0;
for ($i=0; $i < $len; $i++){
$num += strpos($source_string, $code[$i]) * pow(34, $i);
}
return $num;
}
