Question

// Hi, I want to exclude a flag with bitwise operations, but I don’t know how :
// Here are the flags (they come from filesystemiterator)

define('CURRENT_AS_FILEINFO', 0);
define('CURRENT_AS_SELF', 16);
define('CURRENT_AS_PATHNAME', 32);
define('CURRENT_MODE_MASK', 240);
define('KEY_AS_PATHNAME', 0);
define('KEY_AS_FILENAME', 256);
define('FOLLOW_SYMLINKS', 512);
define('KEY_MODE_MASK', 3840);
define('NEW_CURRENT_AND_KEY', 256);
define('SKIP_DOTS', 4096);
define('UNIX_PATHS', 8192);

The user can potentially set any combination of flags.
I need to detect if CURRENT_AS_SELF or CURRENT_AS_PATHNAME was set,
so here is my function so far:

function containsPathnameOrSelfFlag($flags) {
    if ($flags & (CURRENT_AS_PATHNAME | CURRENT_AS_SELF)) {
        return true;
    }
    return false;
}

And here is a test suite :

var_dump(containsPathnameOrSelfFlag(CURRENT_MODE_MASK | CURRENT_AS_PATHNAME)); // true, ok
var_dump(containsPathnameOrSelfFlag(CURRENT_AS_FILEINFO)); // false, ok
var_dump(containsPathnameOrSelfFlag(CURRENT_MODE_MASK | CURRENT_AS_FILEINFO)); // true, but false was expected, because neither CURRENT_AS_SELF nor CURRENT_AS_SELF were set, so my function is wrong

Is it possible to use bitwise operators to make the function pass the third case
( it should return false )
?

The problem I see here is that the CURRENT_MODE_MASK’s bit overlap the CURRENT_AS_SELF
and CURRENT_AS_PATHNAME’s bits :

0000000000010000 : CURRENT_AS_SELF 
0000000000100000 : CURRENT_AS_PATHNAME 
0000000011110000 : CURRENT_MODE_MASK 
0000000100000000 : KEY_AS_FILENAME
0000001000000000 : FOLLOW_SYMLINKS
0000111100000000 : KEY_MODE_MASK
0000000100000000 : NEW_CURRENT_AND_KEY
0001000000000000 : SKIP_DOTS
0010000000000000 : UNIX_PATHS

So every time the user add the CURRENT_MODE_MASK to the flags, my function
will think that the CURRENT_AS_SELF and the CURRENT_AS_PATHNAME were set too, though it’s not the case.
I don’t know how to solve this.

Answer 1

Masks are meant to be anded against the current value for testing, not ored with new values for generation. If you want to test for presence of or use only a single flag, then use only that flag.