Re: Bitwise operations criticism needed

Marek Kilimajer wrote:

Your checks are something like if($user['tom'] & $perm['read']) echo 'Tom can read'; Only the 3rd bit is checked, all others are ignored and won't do any harm. Anyway, the "clean" way of setting permissions is: $user['tom'] = $perm['execute'] | $perm['write'] | $perm['read'];

Understood. It cant be illegal if its set as you described.

$compare = $perm_total & $user_perm; unsets all bits other than 1, 2 and 4, so 0 =< $compare =< 7. However, your first condition already did this.

Ok. So here is the updated code -> -- start code -- <?php $perm = $user = array(); $perm_total = 0; // Permissions from some source like a database/file $perm['execute'] = 1; $perm['write'] = 2;

$perm['read']    = 4;

// User permissions (predetermined) from sessions maybe

$user['tom']            = $perm['read'] | $perm['write'] | $perm['execute'];  // rwx
$user['joe']            = $perm['read'] | $perm['execute'];  // rx

$user['whats_his_face'] = $perm['read'] | $perm['write']; // rw // Set the sum of "source" permissions foreach($perm as $value) {

    $perm_total |= $value;

} echo "<ul>"; // Loop over the users foreach($user as $id => $user_perm) {

    // Compare user bits to permission bits
    $compare = $perm_total & $user_perm;

    // Make it an even 4 bit string (for visual effect)
    $bits_string = sprintf("%03d", decbin( $compare ));

    echo "<li>User: " . $id . "</li>";

    // Check to see if the comparision contains any permission bits
    $can_read    = (($compare & $perm['read']) == $perm['read']) === TRUE ? "TRUE" : "FALSE";
    $can_write   = (($compare & $perm['write']) == $perm['write']) === TRUE ? "TRUE" : "FALSE";
    $can_execute = (($compare & $perm['execute']) == $perm['execute']) === TRUE ? "TRUE" : "FALSE";

    echo "<ul>";
    echo "<li>" . $user_perm . ' -> ' . $bits_string . "</li>";
    echo "<li>Can Read: $can_read</li>";
    echo "<li>Can Write: $can_write</li>";
    echo "<li>Can Execute: $can_execute</li>";

    echo "</ul>";

} echo "</ul>"; ?> -- end code -- So if thats it, now its time to expand on this idea on my end... Thanks