流量单位转换

#格式化流量
public static function formatFlux($flux)
    {
        $unit = ['MB', 'GB', 'TB', 'PB', 'EB', 'ZB', 'YB', 'BB', 'NB', 'DB'];
        $i = 0;
        while (true) {
            if ($flux<1024 && isset($unit[$i])) {
                return ['number' => bcmul($flux, 1, 1), 'unit' => $unit[$i]];
            }

            $i++;

            if (!isset($unit[$i])) {
                return ['number' => bcmul($flux, 1, 1), 'unit' => $unit[$i-1]];
            }

            $flux = bcdiv($flux, 1024, 10);
        }
    }

#将流量转为MB
public static function convertToMB($traffic, $unit)
    {
        $units = ['MB', 'GB', 'TB', 'PB', 'EB', 'ZB', 'YB', 'BB', 'NB', 'DB'];
        if (!in_array($unit, $units, true)) {
            throw new \Exception('转换单位错误');
        }

        $index = array_search($unit, $units);

        return $index==0 ? $traffic : bcmul(bcpow(1024, $index), $traffic, 2);
    }