Converting bytes to short name in PHP

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Sometimes we need to display bytes in more human readable form. Using this function you can easily convert 10 000 000 bytes to 9.54 Mb

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/**
 * @param int $bytes
 * @param null $unit
 * @return string
 */
function byteConvert($bytes, $unit = null)
{
    //Array of latin unit names
    $unitNames = array('b', 'Kb', 'Mb', 'Gb', 'Tb', 'Pb', 'Eb', 'Zb', 'Yb', 'Vb');

    //Is working unit defined
    if(!is_null($unit))
    {
        //make sure that unit is in correct format
        $unit = ucfirst(strtolower($unit));

        //check we know such unit
        if(!in_array($unit, $unitNames))
            $unit = null;
    }

    //are we using custom units?
    if(is_null($unit))
    {
        //get fraction of bytes
        $fraction = log($bytes) / log(1024);

        //How many units do we know
        $knownUnits = count($unitNames);

        //is unit out of known range?
        if ($fraction > $knownUnits)
        {
            $num = $knownUnits;

            $unit = $unitNames[$knownUnits - 1];
        }
        else
        {
            $num = floor($fraction);

            $unit = $unitNames[$num];
        }
    }
    else
    {
        $num = array_search($unit, $unitNames);
    }

    return sprintf('%.2f %s', ($bytes / pow(1024, $num)), $unit);
}

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