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Integer to/from Base62 in PHP
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<?php | |
// Author: Gonçalo Baltazar <me@goncalomb.com> | |
// I place this code in the public domain. | |
/** | |
* Functions to encode/decode an integer to/from base62. | |
* It is limited to positive integers up to BASE62_MAX to make sure it works on | |
* 32-bit systems. | |
*/ | |
// You can change BASE62_CHARS but keep it 62 characters long. | |
define('BASE62_CHARS', '0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ'); | |
define('BASE62_MAX', 2147483647); | |
define('BASE62_MAX_5CHARS', 916132831); | |
/** | |
* Encode int to base62. | |
* By default it returns a string padded to 5 characters. If encoding a number | |
* bigger than BASE62_MAX_5CHARS the string will have 6 characters. | |
* Change the default padding with $pad. | |
*/ | |
function int_to_base62($num, $pad=5) { | |
$n = (int) $num; | |
if ($num != $n || $n < 0 || $n > BASE62_MAX) { | |
// invalid int | |
return null; | |
} | |
$chars = BASE62_CHARS; | |
$str = ''; | |
do { | |
$str = $chars[$n%62] . $str; | |
$n = floor($n/62); | |
} while ($n > 0); | |
return ($pad && $pad > 0 ? str_pad($str, ($pad > 6 ? 6 : $pad), '0', STR_PAD_LEFT) : $str); | |
} | |
/** | |
* Decode int from base62. | |
* If $strict == true only strings with 5 or 6 characters are considered valid. | |
* Change it to false if a $pad other than 5 or 6 was used to encode. | |
*/ | |
function int_from_base62($str, $strict=true) { | |
$str = (string) $str; | |
$l = strlen($str); | |
if ($strict && $l != 6 && $l != 5 || !$strict && ($l < 1 || $l > 6)) { | |
return null; | |
} | |
$powers = array(1, 62, 3844, 238328, 14776336, 916132832); | |
$n = 0; | |
for ($i = 0; $i < $l; ++$i) { | |
$v = strpos(BASE62_CHARS, $str[$l - $i - 1]); | |
if ($v === false) { | |
// invalid char | |
return null; | |
} | |
$n += $v * $powers[$i]; | |
if ($n > BASE62_MAX || is_float($n)) { | |
// in PHP, int "overflows to float" | |
return null; | |
} | |
} | |
return $n; | |
} | |
?> |
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