If you use base_convert to convert a large (eg. 80-bit) hexadecimal to base-36, you might observe:
ABCDEF00001234567890 (hexadecimal) => 3O47RE02JZSW0KS8 (base-36) => ABCDEF00001240000000 (hexadecimal)
This is normal and is due to the loss of precision on large numbers.
I have written a string-based function using the built-in BC Math Extension which will overcome this and similar problems.
<?php
function str_baseconvert($str, $frombase=10, $tobase=36) {
$str = trim($str);
if (intval($frombase) != 10) {
$len = strlen($str);
$q = 0;
for ($i=0; $i<$len; $i++) {
$r = base_convert($str[$i], $frombase, 10);
$q = bcadd(bcmul($q, $frombase), $r);
}
}
else $q = $str;
if (intval($tobase) != 10) {
$s = '';
while (bccomp($q, '0', 0) > 0) {
$r = intval(bcmod($q, $tobase));
$s = base_convert($r, 10, $tobase) . $s;
$q = bcdiv($q, $tobase, 0);
}
}
else $s = $q;
return $s;
}
?>
Typical use-cases:
1. Convert a large arbitrary precision number to base-36.
2. Convert a 32-char hexadecimal UUID (128-bit) to a 25-char base-36 unique key, and vice versa.
Examples:
<?php
$b16 = 'ABCDEF00001234567890';
$b36 = str_baseconvert($b16, 16, 36);
echo ("$b16 (hexadecimal) = $b36 (base-36) \\n");
$uuid = 'ABCDEF01234567890123456789ABCDEF';
$ukey = str_baseconvert($uuid, 16, 36);
echo ("$uuid (hexadecimal) = $ukey (base-36) \\n");
?>
ABCDEF00001234567890 (hexadecimal) = 3o47re02jzqisvio (base-36)
ABCDEF01234567890123456789ABCDEF (hexadecimal) = a65xa07491kf5zyfpvbo76g33 (base-36)
