PHP字节单位转换

function calc($size,$digits=2){ 
  $unit= array("","K","M","G","T","P");
  $base= 1024;
  $i = floor(log($size,$base));
  $n = count($unit);
  if($i >= $n){
    $i=$n-1;
  }
  return round($size/pow($base,$i),$digits)." ".$unit[$i] . "B";
}
echo calc(5632124788522146278);