Bitwise comparison in PHP

Question

I confess I don't really know what I'm doing! I'm pulling some data from SecondLife and parsing it in PHP. The data is an integer from llGetRegionFlags which, in my case, returns 1048592

Now I need to do a bitwise comparison in PHP to figure out which flags are true/false. For example 0x00000040 is used for the "block terraform" flag.

The notations are in hex for each flag, and I have an integer to test against, and the PHP manual suggests integers and shows examples in binary.

So my question really is, given an integer and some hex flags, how do I go about doing the bitwise comparison in PHP? Brainfried! Thanks in advance

score 1 · Accepted Answer · answered Feb 21 '13 at 15:28

1

To determine if a particular bit is turned on, use the & (AND) operator:

if ($data & 0x00000040) {
    // block terraform flag is true
}

If the bit is turned on, the AND operator will return a positive number. If it is turned off, then the AND operator will result in a zero.

answered Feb 21 '13 at 15:28

James Tracy

40
4

Aha thank you! I didn't realise I could compare a hex value against an integer, or how to use hex notation in PHP. Simple when you know how! – Tak Feb 21 '13 at 15:32

score 0 · Answer 2 · answered Feb 21 '13 at 15:28

0

Use a single AND & / OR |

if ($value1 & $value2) { }

The PHP Manual explains more: http://php.net/manual/en/language.operators.bitwise.php

answered Feb 21 '13 at 15:28

mcryan

1,566
10
20

Thanks mcryan, sorry James pipped you to the post! I did try the manual but didn't realise I could compare hex against an integer etc – Tak Feb 21 '13 at 15:33

score 0 · Answer 3 · answered Feb 21 '13 at 15:30

0

You could define the bits required, and check against them to make it look clean. ie

define('BLOCK_TERAFORM', 0x00000040);

....

if($data & BLOCK_TERAFORM) {
  ... do something ...
}

answered Feb 21 '13 at 15:30

Nick Andriopoulos

10,313
6
32
56

Thanks hexblot great idea, keeps it clean – Tak Feb 21 '13 at 15:33

score 0 · Answer 4 · answered Feb 21 '13 at 15:35

0

Usually the bitflags are checked with a piece of code like this:

$blockTerraformFlag = 0x00000040;
$isBlockTerraform = (($RegionFlags & $blockTerraformFlag) == $blockTerraformFlag);

answered Feb 21 '13 at 15:35

Nechoha

3
2

Bitwise comparison in PHP

4 Answers4