PHP if & question

Question

what does this mean "if ($strength & 2) {" in the following: I dont understand the $ 2 part...

    function generatePassword($length=11, $strength=7) {
    $vowels = 'aeuy';
    $consonants = 'bdghjmnpqrstvz';
    if ($strength & 1) {
        $consonants .= 'BDGHJLMNPQRSTVWXZ';
    }
    if ($strength & 2) {
        $vowels .= "AEUY";
    }
    if ($strength & 4) {
        $consonants .= '23456789';
    }
    if ($strength & 8) {
        $consonants .= '@#$%';
    }

    $password = '';
    $alt = time() % 2;
    for ($i = 0; $i < $length; $i++) {
        if ($alt == 1) {
            $password .= $consonants[(rand() % strlen($consonants))];
            $alt = 0;
        } else {
            $password .= $vowels[(rand() % strlen($vowels))];
            $alt = 1;
        }
    }
    return $password;
}

possible duplicate of [What does & in &2 mean in PHP?](http://stackoverflow.com/questions/4705262/what-does-in-2-mean-in-php) — mario, Jun 15 '11 at 05:04

score 4 · Accepted Answer · answered Jun 15 '11 at 05:06

4

& is a bitwise operator. It manipulates the physical bits of a number. & is known as "bitwise AND". Given two numbers, it will create a new number for all of the shared bits in both numbers.

If you line up the bits for two numbers, any matching bits will be in the resulting number.

 7: 00000111
 2: 00000010

 7 & 2 == 2

This is an easy way to store information in a compact manner.

answered Jun 15 '11 at 05:06

lunixbochs

21,757
2
39
47

3

this is the best example of bitwise operations that i have seen, i finally get it. +1 – Ibu Jun 15 '11 at 05:08

score 1 · Answer 2 · edited Jan 09 '13 at 07:53

1

You have used $vowels = 'aeuy'; $consonants = 'bdghjmnpqrstvz'; to change $vowels = 'aeiou'; $consonants = 'bdghjmnpqrstvyz';

edited Jan 09 '13 at 07:53

partlov

13,789
6
63
82

answered Jan 09 '13 at 07:32

Prabakaran R

11
1

alex · Answer 3 · 2011-06-15T05:08:41.883

& is the and bitwise operator.

$a & $b Bits that are set in both $a and $b are set.

$strength appears to be an option for the strength of the password.

2 in binary is 00000010. If $strength was 2, then it would run that condition because the resulting number would be 2 (as both bits are set the same in both numbers).

It $strength were 1 (0000001), when bitwised with 2 would produce 0, and the condition would be false.

bjornd · Answer 4 · 2011-06-15T05:10:38.707

1

This if ($strength & 2) { means "if the second bit is equal to 1". Suppose $strength = 6 or 110 in binary system, at the same time binary representation of 2 is 10. So & operator does a bitwise and operation:

You get positive number only when the second bit of $strength is equal to 1, otherwise you get 0.

edited Jun 15 '11 at 05:10

answered Jun 15 '11 at 05:04

bjornd

22,397
4
57
73

score 1 · Answer 5 · answered Jun 15 '11 at 05:08

It's a bitwise comparison - see http://www.litfuel.net/tutorials/bitwise.htm for a basic description of what is going on.

If the author had defined some nice constants, it would read more like:

function generatePassword($length = 11, $strength = STRENGTH_INCLUDE_UPPERCASE & STRENGTH_INCLUDE_DIGITS & STRENGTH_INCLUDE_SYMBOLS) {
  if ($strength & STRENGTH_INCLUDE_UPPERCASE) { ...
  if ($strength & STRENGTH_INCLUDE_DIGITS) { ...
  if ($strength & STRENGTH_INCLUDE_SYMBOLS { ...

which would make it far more readable for you and maintainable in the future.

score 0 · Answer 6 · answered Jun 15 '11 at 05:06

0

& is a bitwise operator. Mainly it tells you if the binary form of $strength has a 1 on position:

2 for 2
3 for 4
4 for 8

answered Jun 15 '11 at 05:06

Tudor Constantin

26,330
7
49
72

score 0 · Answer 7 · answered Jun 15 '11 at 05:12

the '&' is the a bitwise operator. returns 1 not a boolean. Well,if you are looking do a comparison use the "==" operator.

replace

if ($strength & 1) {
    $consonants .= 'BDGHJLMNPQRSTVWXZ';
}

by

if ($strength == 1) {
    $consonants .= 'BDGHJLMNPQRSTVWXZ';
}

PHP if & question

7 Answers7