Bits and bitmask are something I have been struggling to understand for a while, but I would like to learn how to use them for settings and things like that in PHP.
I have finally found a class that claims to do exactly that, and as I can tell, it seems to work, but I am not sure if it is the best way of doing this. I will post the class file with example code below to show it in working order.
Please if you have experience, tell me if it can be improved, for performance or anything else. I really want to learn this, and I have been reading up on it, but it is a difficult one for me to grasp so far.
The class...
<?php
class bitmask
{
/**
* This array is used to represent the users permission in usable format.
*
* You can change remove or add valuesto suit your needs.
* Just ensure that each element defaults to false. Once you have started storing
* users permsisions a change to the order of this array will cause the
* permissions to be incorectly interpreted.
*
* @type Associtive array
*/
public $permissions = array(
"read" => false,
"write" => false,
"delete" => false,
"change_permissions" => false,
"admin" => false
);
/**
* This function will use an integer bitmask (as created by toBitmask())
* to populate the class vaiable
* $this->permissions with the users permissions as boolean values.
* @param int $bitmask an integer representation of the users permisions.
* This integer is created by toBitmask();
*
* @return an associatve array with the users permissions.
*/
public function getPermissions($bitMask = 0)
{
$i = 0;
foreach ($this->permissions as $key => $value)
{
$this->permissions[$key] = (($bitMask & pow(2, $i)) != 0) ? true : false;
// Uncomment the next line if you would like to see what is happening.
//echo $key . " i= ".strval($i)." power=" . strval(pow(2,$i)). "bitwise & = " . strval($bitMask & pow(2,$i))."<br>";
$i++;
}
return $this->permissions;
}
/**
* This function will create and return and integer bitmask based on the permission values set in
* the class variable $permissions. To use you would want to set the fields in $permissions to true for the permissions you want to grant.
* Then call toBitmask() and store the integer value. Later you can pass that integer into getPermissions() to convert it back to an assoicative
* array.
*
* @return int an integer bitmask represeting the users permission set.
*/
function toBitmask()
{
$bitmask = 0;
$i = 0;
foreach ($this->permissions as $key => $value)
{
if ($value)
{
$bitmask += pow(2, $i);
}
$i++;
}
return $bitmask;
}
}
?>
How do I set/save the permissions as a bitmask value?
<?php
/**
* Example usage
* initiate new bitmask object
*/
$perms = new bitmask();
/**
* How to set permissions for a user
*/
$perms->permissions["read"] = true;
$perms->permissions["write"] = true;
$perms->permissions["delete"] = true;
$perms->permissions["change_permissions"] = true;
$perms->permissions["admin"] = false;
// Converts to bitmask value to store in database or wherever
$bitmask = $perms->toBitmask(); //in this example it is 15
$sql = "insert into user_permissions (userid,permission) values(1,$bitmask)";
echo $sql; //you would then execute code to insert your sql.
?>
Example of taking the bitmask value and returning a true/false for each array item based on the bit value....
<?php
/**
* Example usage to get the bitmask value from database or session/cache.... then put it to use.
* $permarr returns an array with true/false for each array value based on the bit value
*/
$permarr = $perms->getPermissions($bitmask);
if ($permarr["read"])
{
echo 'user can read: <font color="green">TRUE</font>';
}
else {
echo 'user can read: <font color="red">FALSE</font>';
}
//user can WRITE permission
if ($permarr["write"])
{
echo '<br>user can write: <font color="green">TRUE</font>';
}
else {
echo '<br>user can write: <font color="red">FALSE</font>';
}
?>
