Bitwise operators?

issue9mm

Okay, I understand (so far) using bit vectors for storing boolean values, and using the AND operator to test the values against the mask conditions.

What I can't seem to figure out right now, is how to take a given value and flip one of the bits in it.

ie: $bit = '0001';

How do I change bit from '0001' to '0101'?

I was thinking it was with the NOT operator (~), but so far, when I use that, then print out $bit, it returns illegible characters and whatnot.

Any tips?

-9mm-

Interitus

I can't confirm this atm, but I believe this behaviour is because you are performing the bitwise operations on the ASCII values of the string '0001' rather than the actual bytes.

For a tutorial on how to properly use the bitwise operators of PHP, check out

http://www.zend.com/zend/spotlight/code-gallery-wade2.php

floR

$bit = 1; // 0001
$flip = 4; // 0100
$newbit = $bit | $flip; // 0001 | 0100 = 0101 (=5)

Is that what you mean?

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

issue9mm

Flor. Thank you, thank you, thank you.

That works precisely, except that it won't flip a bit from "on" to "off". Is there something that I'm missing there too?

Interitus: I'm not performing the operations on the ASCII values as I'm quoting them in single quotes, which then causes PHP to treat them as single-character entries, or binary, as the case may be. Thanks though.

-b-

Weedpacket

Originally posted by issue9mm
Flor. Thank you, thank you, thank you.

That works precisely, except that it won't flip a bit from "on" to "off". Is there something that I'm missing there too?

Well, OR (|) would just set a bit to on - if it's on already it won't have any effect. If you're wanting a toggle, use XOR (^).

Interitus: I'm not performing the operations on the ASCII values as I'm quoting them in single quotes, which then causes PHP to treat them as single-character entries, or binary, as the case may be. Thanks though.

No, putting 0101 in single quotes would get PHP to treat it as a string of four ASCII characters: chr(48).chr(49).chr(48).chr(49). The bitwise operators will act on those ASCII values, like Interitus says.

issue9mm

Actually, you're exactly right.

I started using Xor to toggle, and stopped using binary representations, and everything is working perfectly.

What threw me off tho, is that if I took '0011', and ANDed it with '0010', the result was perfectly correct.

It was only Xor that wasn't working correctly.

I've modified the masks to stop using '0001', '0010', '0100', etc., to instead just use '1 <<0', '1 << 1', '1 << 2', and am performing operations on the ASCII numbers, and, as I said, things are working perfectly.

Thanks for all the help from everyone.

My next question is, is there a way to get PHP to treat binary strings as binary?

I don't really care, since it's working fine, but am curious if there is a way.

Thanks again,
-9mm-

Weedpacket

Originally posted by issue9mm
My next question is, is there a way to get PHP to treat binary strings as binary?

What, you mean by using bin2dec()?