Bitwise Boolean Values in PHP?

Anon

Hello all!

How do I check for bitwise boolean values in php. Like say I have the number 7 and I want to check for the bool bit 2^1, which is true because 7=111. How would I check that? (This is a flag system)

Thanks!

Joe

[deleted]

Manuals are cool.
http://www.php.net/manual/en/language.operators.bitwise.php

Anon

Thanks but that doesnt answer my question, I already read it.

polson

Here's an example, to alternate row colors using bitwise & :

<table>
<?php
for($i = 0; $i <= 10; $i++) {

    $bgcolor = ($i & 1) ? '#eeeeee' : '#e0e0e0'; 

    print "<tr bgcolor='$bgcolor'>\n";
    print "\t<td>$i</td>\n</tr>\n"; 
}

?>
</table>

Anon

Again, thanks but this is still not what I am asking for. Say I have the number 7 and I want to check for the bool bit 2^1, which is true because 7=111. How would I check that?

Joe

polson

actually, it's exactly what you want and demonstrates going from number 0 to 10. here's another example, using 7 :

if (7 & 1) {
print 'yes!';
} else {
print 'no.';
}

Anon

Philip,

Thanks for the insight, I will try to do that... Say I am trying to determine the following in an online php game:

User Flags:

No Health Items 1
No Items 2
Weapons Stay 4
No Falling Damage 8
Instant Powerups 16
Same Level 32
Repawn Player Farthest 512
Force Player Respawn 1024
No Armor 2048

Any combination of these can be on or off, so you would just add up the the ones that are on and get the resultant number: say Everything is on, you would get the number 3647. I was wondering if there is an elegant way of determining the true or false value of each of those items by using bitwise / boolean math on the resultant 3647, as I believe you can do in C. I am not very good with boolean or bitwise math yet and am trying to learn.

Thanks again, everyone.

Joe

hometoast

philip did answer your question. his example just tested the last bit with ($x & 1).
if 7 = 111
and 2 = 010
echo (7 & 2) will tell you if 2nd bit is set.
echo (7 & 4) will yield true because 4 = 100

so
echo ($x & 2^$bit)
will test whatever $bit you need to test.

PLEASE tell me if my logic/syntax is incorrect. and good luck

kparker

Bitwise arithmetic in PHP works exactly as it does in C. So do hexidecimal numeric constants, so you can use the visually more understandable

No Health Items 0x01
No Items 0x02
Weapons Stay 0x04
No Falling Damage 0x08
Instant Powerups 0x10
Same Level 0x20
Repawn Player Farthest 0x200
Force Player Respawn 0x400
...

Then, as far as testing:

if ((capabilities & 0x20) == 0x20)
   {
   // same level code goes here...
   }