Question

I’m looking for a way to figure out the passed arguments (as well as their order) in a function out of a possibly precalculated integer by bitwise operators. I’m already aware that I should be using numbers like 2^n for the constants that can be passed (due to bitwise calculations) but I don’t have an idea how to decompose that.

So to sum up:

1. How can I figure out that 1 and 4 has been passed to the following function
2. Can the order of these be obtained somehow, perhaps by some specific bitwise operator?

Here’s an example displaying what I mean.

$inst = new SomeClass;
$inst->some_func( SomeClass::RULE1 | SomeClass::RULE3 );

class SomeClass {

    const RULE1 = 1;
    const RULE2 = 2;
    const RULE3 = 4;

    public function some_func($arg) {
        // what are the RULE's in the $arg here?
    }

Please note that I’m trying to figure out how to work with bitwise operators as function arguments. So I’m not looking for other solutions like passing an array to the function or using func_get_args().

Answer 1

Well lets take a look (syntax is for PHP 5.4):

const RULE1 = 0b0000 0001; // 1
const RULE2 = 0b0000 0010; // 2
const RULE3 = 0b0000 0100; // 4

So when you pass in $inst->some_func( SomeClass::RULE1 | SomeClass::RULE3 );;

The arg will be 0b0000 0101.

So now to actually use this, we would do:

if ($arg & self::RULE1) // check if the RULE1 bit is ON (ie: equals 1)
{
    // do stuff based on RULE1;
}

if ($arg & self::RULE2) // check if the RULE2 bit is ON
{
    // do stuff based on RULE2;
}

// etc

Hopefully that helps!

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Can the order of these be obtained somehow, perhaps by some specific bitwise operator?

That wouldn’t be possible to do, because RULE1 | RULE3 and RULE3 | RULE1 both produce the exact same binary sequence.