PHP 10进制与62进制互转，可用于生成短网址

<?php

/**
 * 生成短连接的相关方法--通过记录ID换算成为58位的字符串(十进制转换成58进制)
 */
class BaseConvert {

    const key_code_64 = '0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ_$';
    const key_code_58 = '123456789abcdefghijkmnopqrstuvwxyzABCDEFGHJKLMNPQRSTUVWXYZ';

    /**
     * 十进制数转换成其它进制
     * 可以转换成2-62任何进制
     *
     * @param integer $num
     * @param integer $to
     * @return string
     */
    static function to($num, $to = 58) {
        if ($to == 10 || $to > 64 || $to < 2) {
            return $num;
        }

        if ($to == 58) {
            $dict = self::key_code_58;
        } else {
            $dict = self::key_code_64;
        }

        $ret = '';
        do {
            $ret = $dict[bcmod($num, $to)] . $ret;
            $num = bcdiv($num, $to);
        } while ($num > 0);
        return $ret;
    }

    /**
     * 其它进制数转换成十进制数
     * 适用2-62的任何进制
     *
     * @param string $num
     * @param integer $from
     * @return number
     */
    static function from($num, $from = 58) {
        if ($from == 10 || $from > 64 || $from < 2) {
            return $num;
        }

        if ($from == 58) {
            $dict = self::key_code_58;
        } else {
            $dict = self::key_code_64;
        }

        $num = strval($num);
        $len = strlen($num);
        $dec = 0;
        for ($i = 0; $i < $len; $i++) {
            $pos = strpos($dict, $num[$i]);
            if ($pos >= $from) {
                continue; // 如果出现非法字符，会忽略掉。比如16进制中出现w、x、y、z等
            }
            $dec = bcadd(bcmul(bcpow($from, $len - $i - 1), $pos), $dec);
        }
        return $dec;
    }

    /**
     * 数字的任意进制转换
     *
     * @param integer|string $number
     * @param integer $to 目标进制数
     * @param integer $from 源进制数
     * @return string
     */
    static function radix($number, $to = 64, $from = 10) {
        // 先转换成10进制
        $number = self::from($number, $from);
        // 再转换成目标进制
        $number = self::to($number, $to);
        return $number;
    }
}