JasonDavis JasonDavis - 5 months ago 39
PHP Question

Why should I use bitwise/bitmask in PHP?

I am working on a user-role / permission system in PHP for a script.

Below is a code using a bitmask method for permissions that I found on phpbuilder.com.

Below that part is a much simpler version w3hich could do basicly the same thing without the bit part.

Many people have recommended using bit operators and such for settings and other things in PHP, I have never understood why though. In the code below is there ANY benefit from using the first code instead of the second?

<?php
/**
* Correct the variables stored in array.
* @param integer $mask Integer of the bit
* @return array
*/
function bitMask($mask = 0) {
$return = array();
while ($mask > 0) {
for($i = 0, $n = 0; $i <= $mask; $i = 1 * pow(2, $n), $n++) {
$end = $i;
}
$return[] = $end;
$mask = $mask - $end;
}
sort($return);
return $return;
}


define('PERMISSION_DENIED', 0);
define('PERMISSION_READ', 1);
define('PERMISSION_ADD', 2);
define('PERMISSION_UPDATE', 4);
define('PERMISSION_DELETE', 8);

//run function
// this value would be pulled from a user's setting mysql table
$_ARR_permission = bitMask('5');

if(in_array(PERMISSION_READ, $_ARR_permission)) {
echo 'Access granted.';
}else {
echo 'Access denied.';
}
?>


non-bit version

<?PHP
/*
NON bitwise method
*/

// this value would be pulled from a user's setting mysql table
$user_permission_level = 4;

if($user_permission_level === 4) {
echo 'Access granted.';
}else {
echo 'Access denied.';
}

?>

Answer

Why not just do this...

define('PERMISSION_DENIED', 0);
define('PERMISSION_READ', 1);
define('PERMISSION_ADD',  2);
define('PERMISSION_UPDATE', 4);
define('PERMISSION_DELETE', 8);

//run function
// this value would be pulled from a user's setting mysql table
$_ARR_permission = 5;

if($_ARR_permission & PERMISSION_READ) {
    echo 'Access granted.';
}else {
    echo 'Access denied.';
}

You can also create lots of arbitrary combinations of permissions if you use bits...

$read_only = PERMISSION_READ;
$read_delete = PERMISSION_READ | PERMISSION_DELETE;
$full_rights = PERMISSION_DENIED | PERMISSION_READ | PERMISSION_ADD | PERMISSION_UPDATE | PERMISSION_DELETE;

//manipulating permissions is easy...
$myrights = PERMISSION_READ;
$myrights |= PERMISSION_UPDATE;    // add Update permission to my rights
Comments