function format_bi($value, $round = '2', $sf = '3')
{
    if ($value < "0") {
        $neg = 1;
        $value = $value * -1;
    }
    $sizes = array('', 'k', 'M', 'G', 'T', 'P', 'E');
    $ext = $sizes[0];
    for ($i = 1; $i < count($sizes) && $value >= 1024; $i++) {
        $value = $value / 1024;
        $ext = $sizes[$i];
    }
    if ($neg) {
        $value = $value * -1;
    }
    return format_number_short(round($value, $round), $sf) . $ext;
}

 /**
  * @dataProvider providerFormatNumberShort
  */
 public function testFormatNumberShort($value, $sf, $result)
 {
     $this->assertSame($result, format_number_short($value, $sf));
 }