短网址技术常用的Base62编解码

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短网址技术常用的Base62编解码

发布： 2012-03-19 21:30

使用Base62能编码出与URL字符不冲突，并且长度与Base64几乎相等的字符串，很有优化与使用便利的优势。

下面示例代码所使用bcmath库，在php4.0.4时已经引入到核心，更新的版本中不需要额外安装bcmath库。

[code type="php']

/**
* Converts a base 10 number to any other base.
*
* @param int $val Decimal number
* @param int $base Base to convert to. If null, will use strlen($chars) as base.
* @param string $chars Characters used in base, arranged lowest to highest. Must be at least $base characters long.
*
* @return string Number converted to specified base
*/
function base_encode($val, $base=62, $chars='0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ') {
if(!isset($base)) $base = strlen($chars);
$str = '';
do {
$m = bcmod($val, $base);
$str = $chars[$m] . $str;
$val = bcdiv(bcsub($val, $m), $base);
} while(bccomp($val,0)>0);
return $str;
}

/**
* Convert a number from any base to base 10
*
* @param string $str Number
* @param int $base Base of number. If null, will use strlen($chars) as base.
* @param string $chars Characters use in base, arranged lowest to highest. Must be at least $base characters long.
*
* @return int Number converted to base 10
*/
function base_decode($str, $base=62, $chars='0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ') {
if(!isset($base)) $base = strlen($chars);
$len = strlen($str);
$val = 0;
$arr = array_flip(str_split($chars));
for($i = 0; $i < $len; ++$i) {
$val = bcadd($val, bcmul($arr[$str[$i]], bcpow($base, $len-$i-1)));
}
return $v
[/code]

原文： http://qtchina.tk/?q=node/640