Yoone Yoone - 2 months ago 17
PHP Question

Convertions between decimal and base 36

I want to convert numbers in base 36 using PHP. The function

base_convert
is not working because I want to convert large numbers: I don't get my initial number if I convert it again from base 36 to decimal.

I tried some function given on multiple websites, but I never get the same result. Also, these two websites (in Javascript) give the same result:



For example
1010701001118000000000000000
has to be converted to
3IZS0ZE1RQ68W8SSW4
.

Here are the functions I tried (and which don't work):


Answer

Here are two simple functions using an algorithm found on Wikipedia, while using bcmath to get the calculations even for very large numbers right:

function fromDecimalToBase($in, $to) {
    $in = (string) $in;
    $out = '';

    for ($i = strlen($in) - 1; $i >= 0; $i--) {
        $out = base_convert(bcmod($in, $to), 10, $to) . $out;
        $in = bcdiv($in, $to);
    }

    return preg_replace('/^0+/', '', $out);
}

function fromBaseToDecimal($in, $from) {
    $in = (string) $in;
    $out = '';

    for ($i = 0, $l = strlen($in); $i < $l; $i++) {
        $x = base_convert(substr($in, $i, 1), $from, 10);
        $out = bcadd(bcmul($out, $from), $x);
    }

    return preg_replace('/^0+/', '', $out);
}

However, I get 3izs0ze1rq66tifrpc for the number you've provided - maybe your conversion was wrong there?

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