Simple Byte-size handling class

bytes.php

<?php

class Bytes
{
    private $sizeInBytes;
    private static $units = array('B', 'KB', 'MB', 'GB', 'TB', 'PB', 'EB', 'ZB', 'YB');

    public function __construct($sizeInBytes)
    {
        $this->sizeInBytes = floatval($sizeInBytes);
    }

    public function  __toString ()
    {
        return $this->ToString();
    }

    public function ToString($unit = null, $decimalPrecision = 2)
    {
        $orderOfMagnitude = 0;
        $newSize = $this->sizeInBytes;

        if ($unit === null) {
            for ($i = 0, $size = $this->sizeInBytes; $size > 1024 && isset(self::$units[$i + 1]); $i++) {
                $size /= 1024;
            }
            $orderOfMagnitude = $i;
            $newSize = $size;
        }
        elseif (!in_array($unit, self::$units)) {
            $pow = floor(log($this->sizeInBytes) / log(1024));
            $orderOfMagnitude = array_search($pow, self::$units);
            $newSize /= pow(1024, $orderOfMagnitude);
        }

        return sprintf('%.' . $decimalPrecision . 'f ' . self::$units[$orderOfMagnitude], $newSize);
    }

    public function Convert($unit)
    {
        switch ($unit) {
            case "k":
            case "K":
            case "Ki":
                $pow = 1;
                break;
            case "M":
            case "Mi":
                $pow = 2;
                break;
            case "G":
            case "Gi":
                $pow = 3;
                break;
            case "T":
            case "Ti":
                $pow = 4;
                break;
            case "P":
            case "Pi":
                $pow = 5;
                break;
            case "E":
            case "Ei":
                $pow = 6;
                break;
            case "Z":
            case "Zi":
                $pow = 7;
                break;
            case "Y":
            case "Yi":
                $pow = 8;
                break;
            default:
                $pow = 0;
        }

        return $this->sizeInBytes / pow(1024, $pow);
    }

    public static function Size($size)
    {
        return new Bytes($size);
    }

    public static function FromFile($filename)
    {
        if (file_exists($filename)) {
            return new Bytes(filesize($filename));
        }
        throw new Exception("File '" . $filename . "' not found.");
    }
}