Question

I need a base_convert() function that works from base 2 up to base 62 but I’m missing the math I need to use, I know that due to the limitations of PHP I need to make use of bcmath, which is fine.

Functions like these convert a number to and from base 10 to another base up to 62, but I want to implement the same functionality of base_convert(), e.g.: a only one function that can convert between arbitrary bases.

I’ve found a function that seems to do this, but it gives me the feeling of having some redundant and slow code and I would like to tweak it a little bit if I knew German, which I don’t. =(

Here is a more readable version of the function:

function bc_base_convert($value, $quellformat, $zielformat)
{
    $vorrat = '0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ';

    if (min($quellformat, $zielformat) < 2)
    {
        trigger_error('Bad Format min: 2', E_USER_ERROR);
    }

    if (max($quellformat, $zielformat) > strlen($vorrat))
    {
        trigger_error('Bad Format max: ' . strlen($vorrat), E_USER_ERROR);
    }

    $dezi = '0';
    $level = 0;
    $result = '';
    $value = trim(strval($value), "\r\n\t +");
    $vorzeichen = '-' === $value{0} ? '-' : '';
    $value = ltrim($value, "-0");
    $len = strlen($value);

    for ($i = 0; $i < $len; $i++)
    {
        $wert = strpos($vorrat, $value{$len - 1 - $i});

        if (FALSE === $wert)
        {
            trigger_error('Bad Char in input 1', E_USER_ERROR);
        }

        if ($wert >= $quellformat)
        {
            trigger_error('Bad Char in input 2', E_USER_ERROR);
        }

        $dezi = bcadd($dezi, bcmul(bcpow($quellformat, $i), $wert));
    }

    if (10 == $zielformat)
    {
        return $vorzeichen . $dezi; // abkürzung
    }

    while (1 !== bccomp(bcpow($zielformat, $level++), $dezi));

    for ($i = $level - 2; $i >= 0; $i--)
    {
        $factor = bcpow($zielformat, $i);
        $zahl = bcdiv($dezi, $factor, 0);
        $dezi = bcmod($dezi, $factor);
        $result .= $vorrat{$zahl};
    }

    $result = empty($result) ? '0' : $result;

    return $vorzeichen . $result;
}

Can anyone explain me the above function or give me some lights on the process of direct conversion between arbitrary bases?

Answer 1

As of PHP 5.3.2 both bc_math and gmp now support bases up to 62, so you can just do:

echo gmp_strval(gmp_init($mynumber, $srcbase), $destbase);

or the bc_math equivalent.