Divide Two Arbitrary Precision Numbers

Decimal to binary conversion, using BC Math.
Note: this function is VERY slow if the decimal number is too big!

<?
function bc_decbin($dec_str) {
if (strlen($dec_str)>0) {
$bin_str = '';
do {
if (((int)$dec_str[strlen($dec_str)-1] % 2) === 0)
$bin_str .= '0';
else
$bin_str .= '1';

$dec_str = bcdiv($dec_str, '2');
} while ($dec_str!='0');

return strrev($bin_str);
}
else
return null;
}
?>