Руководство and php

echo <<<EOH

--------- --------- -- ---------
result value op test
--------- --------- -- ---------
EOH;/*
* Here are the examples.
*/$values = array(0, 1, 2, 4, 8);
$test = 1 + 4;

echo

"n Bitwise AND n";
foreach ($values as $value) {
$result = $value & $test;
printf($format, $result, $value, '&', $test);
}

echo

"n Bitwise Inclusive OR n";
foreach ($values as $value) {
$result = $value | $test;
printf($format, $result, $value, '|', $test);
}

echo

echo

"n--- BIT SHIFT RIGHT ON NEGATIVE INTEGERS ---n";$val = -4;
$places = 1;
$res = $val >> $places;
p($res, $val, '>>', $places, 'copy of sign bit shifted into left side');$val = -4;
$places = 2;
$res = $val >> $places;
p($res, $val, '>>', $places, 'bits shift out right side');$val = -4;
$places = 3;
$res = $val >> $places;
p($res, $val, '>>', $places, 'same result as above; can not shift beyond -1');

echo

"n--- BIT SHIFT LEFT ON POSITIVE INTEGERS ---n";$val = 4;
$places = 1;
$res = $val << $places;
p($res, $val, '<<', $places, 'zeros fill in right side');$val = 4;
$places = (PHP_INT_SIZE * 8) - 4;
$res = $val << $places;
p($res, $val, '<<', $places);$val = 4;
$places = (PHP_INT_SIZE * 8) - 3;
$res = $val << $places;
p($res, $val, '<<', $places, 'sign bits get shifted out');$val = 4;
$places = (PHP_INT_SIZE * 8) - 2;
$res = $val << $places;
p($res, $val, '<<', $places, 'bits shift out left side');

echo

"n--- BIT SHIFT LEFT ON NEGATIVE INTEGERS ---n";$val = -4;
$places = 1;
$res = $val << $places;
p($res, $val, '<<', $places, 'zeros fill in right side');$val = -4;
$places = (PHP_INT_SIZE * 8) - 3;
$res = $val << $places;
p($res, $val, '<<', $places);$val = -4;
$places = (PHP_INT_SIZE * 8) - 2;
$res = $val << $places;
p($res, $val, '<<', $places, 'bits shift out left side, including sign bit');/*
* Ignore this bottom section,
* it is just formatting to make output clearer.
*/function p($res, $val, $op, $places, $note = '') {
$format = '%0' . (PHP_INT_SIZE * 8) . "bn";printf("Expression: %d = %d %s %dn", $res, $val, $op, $places);

echo

" Decimal:n";
printf(" val=%dn", $val);
printf(" res=%dn", $res);

echo

" Binary:n";
printf(' val=' . $format, $val);
printf(' res=' . $format, $res);

if (

$note) {
echo " NOTE: $noten";
}

echo

Sometimes I need a custom PHP Object that holds several boolean TRUE or FALSE values. I could easily include a variable for each of them, but as always, code has a way to get unweildy pretty fast. A more intelligent approach always seems to be the answer, even if it seems to be overkill at first.

I start with an abstract base class which will hold a single integer variable called $flags. This simple integer can hold 32 TRUE or FALSE boolean values. Another thing to consider is to just set certain BIT values without disturbing any of the other BITS -- so included in the class definition is the setFlag($flag, $value) function, which will set only the chosen bit. Here's the abstract base class definition:

<?php# BitwiseFlag.phpabstract class BitwiseFlag
{
  protected $flags;/*
   * Note: these functions are protected to prevent outside code
   * from falsely setting BITS. See how the extending class 'User'
   * handles this.
   *
   */
  protected function isFlagSet($flag)
  {
    return (($this->flags & $flag) == $flag);
  }

  protected function

setFlag($flag, $value)
  {
    if($value)
    {
      $this->flags |= $flag;
    }
    else
    {
      $this->flags &= ~$flag;
    }
  }
}?>

The class above is abstract and cannot be instantiated, so an extension is required. Below is a simple extension called User -- which is severely truncated for clarity. Notice I am defining const variables AND methods to use them.

<?php# User.phprequire('BitwiseFlag.php');

class

User extends BitwiseFlag
{
  const FLAG_REGISTERED = 1; // BIT #1 of $flags has the value 1
  const FLAG_ACTIVE = 2;     // BIT #2 of $flags has the value 2
  const FLAG_MEMBER = 4;     // BIT #3 of $flags has the value 4
  const FLAG_ADMIN = 8;      // BIT #4 of $flags has the value 8public function isRegistered(){
    return $this->isFlagSet(self::FLAG_REGISTERED);
  }

  public function

isActive(){
    return $this->isFlagSet(self::FLAG_ACTIVE);
  }

  public function

isMember(){
    return $this->isFlagSet(self::FLAG_MEMBER);
  }

  public function

isAdmin(){
    return $this->isFlagSet(self::FLAG_ADMIN);
  }

  public function

setRegistered($value){
    $this->setFlag(self::FLAG_REGISTERED, $value);
  }

  public function

setActive($value){
    $this->setFlag(self::FLAG_ACTIVE, $value);
  }

  public function

setMember($value){
    $this->setFlag(self::FLAG_MEMBER, $value);
  }

  public function

setAdmin($value){
    $this->setFlag(self::FLAG_ADMIN, $value);
  }

  public function

__toString(){
    return 'User [' .
      ($this->isRegistered() ? 'REGISTERED' : '') .
      ($this->isActive() ? ' ACTIVE' : '') .
      ($this->isMember() ? ' MEMBER' : '') .
      ($this->isAdmin() ? ' ADMIN' : '') .
    ']';
  }
}?>

This seems like a lot of work, but we have addressed many issues, for example, using and maintaining the code is easy, and the getting and setting of flag values make sense. With the User class, you can now see how easy and intuitive bitwise flag operations become.

<?phprequire('User.php')$user = new User();
$user->setRegistered(true);
$user->setActive(true);
$user->setMember(true);
$user->setAdmin(true);

echo

$user;  // outputs: User [REGISTERED ACTIVE MEMBER ADMIN]?>

<?php// The various details a vehicle can have
    $hasFourWheels = 1;
    $hasTwoWheels  = 2;
    $hasDoors      = 4;
    $hasRedColour  = 8;$bike          = $hasTwoWheels;
    $golfBuggy     = $hasFourWheels;
    $ford          = $hasFourWheels | $hasDoors;
    $ferrari       = $hasFourWheels | $hasDoors | $hasRedColour;$isBike        = $hasFourWheels & $bike; # False, because $bike doens't have four wheels
    $isGolfBuggy   = $hasFourWheels & $golfBuggy; # True, because $golfBuggy has four wheels
    $isFord        = $hasFourWheels & $ford; # True, because $ford $hasFourWheels?>

And you can apply this to a lot of things, for example, security:

<?php// Security permissions:
    $writePost = 1;
    $readPost = 2;
    $deletePost = 4;
    $addUser = 8;
    $deleteUser = 16;// User groups:
    $administrator = $writePost | $readPosts | $deletePosts | $addUser | $deleteUser;
    $moderator = $readPost | $deletePost | $deleteUser;
    $writer = $writePost | $readPost;
    $guest = $readPost;// function to check for permission
    function checkPermission($user, $permission) {
        if($user & $permission) {
            return true;
        } else {
            return false;
        }
    }// Now we apply all of this!
    if(checkPermission($administrator, $deleteUser)) {
        deleteUser("Some User"); # This is executed because $administrator can $deleteUser
    }?>

Once you get your head around it, it's VERY useful! Just remember to raise each value by the power of two to avoid problems

The easiest way to resolve a bitwise  shift operators is my multiply or dividing each step by two for left shift or right shift respectively

Example:

LEFT SHIFT

<?php echo 8 << 3; //64 ?>



//same as

<?php echo 8 * 2 * 2 * 2; ?>



RIGHT SHIFT

<?php echo 8 >> 3; //1 ?>



//same as

<?php echo ((8/2)/2)/2; //1 ?>



//Solving on a paper 8/2 = 4/2 = 2/2 = 1

<?php
    const    FLAG_A    =    0b0001,
            FLAG_B    =    0b0010,
            FLAG_C    =    0b0100,
            FLAG_D    =    0b1000;

                const   

COMBO_BC = FLAG_B | FLAG_C;$bitmask = 0b000;// Setting individual flags.
    $bitmask |=    FLAG_B;        // Sets FLAG_B (=2)
    $bitmask |=    FLAG_C;        // also sets FLAG_C (=4)

        // Testing single or multiple flags.

echo (bool)( $bitmask & FLAG_B );                            // True, B is set.echo (bool)( $bitmask & (FLAG_A | FLAG_B) );                // True, A or B is set.echo (bool)( $bitmask & FLAG_B and $bitmask & FLAG_C );        // True, B and C are set.
    echo (bool)( ( $bitmask & (FLAG_B | FLAG_C) ) ^ (FLAG_B | FLAG_C) );    // False if B and C are set.
    echo (bool)( ( $bitmask & COMBO_BC ) ^ COMBO_BC );            // False if B and C are set.echo (bool)( $bitmask & FLAG_C and $bitmask & FLAG_D );        // False, C and D are NOT BOTH set.
    echo (bool)( ( $bitmask & (FLAG_C | FLAG_D) ) ^ (FLAG_C | FLAG_D) );    // True, if C and D are NOT BOTH set.

        // Resetting single flag.

$bitmask &= $bitmask ^ FLAG_B;    // Unsets B
    $bitmask &= $bitmask ^ FLAG_A;    // A remains unset.
    var_dump( $bitmask );            // Only C still set (=4)

        // Resetting multiple flags.

$bitmask &= $bitmask ^ ( FLAG_C | FLAG_D );    // Unsets C and/or D
    var_dump( $bitmask );            // No flags set (=0)

<?php
function bitxor($str, $key) {
    $xorWidth = PHP_INT_SIZE*8;
    // split
    $o1 = str_split($str, $xorWidth);
    $o2 = str_split(str_pad('', strlen($str), $key), $xorWidth);
    $res = '';
    $runs = count($o1);
    for($i=0;$i<$runs;$i++)
        $res .= decbin(bindec($o1[$i]) ^ bindec($o2[$i]));      
    return $res;
}
?>

Note that this function works only with decimal numbers - other types can be converted with pack().

<?phpfunction rotate ( $decimal, $bits) {$binary = decbin($decimal);

  return (

bindec(substr($binary, $bits).substr($binary, 0, $bits))
  );

}

// Rotate 124 (1111100) to the left with 1 bitsecho rotate(124, 1);// = 121 (1111001)

// Rotate 124 (1111100) to the right with 3 bits

echo rotate(124, -3);// = 79 (1001111)?>

<?php
    // We want to know the red, green and blue values of this color :
    $color = 0xFEA946 ;$red = $color >> 16 ;
    $green = ($color & 0x00FF00) >> 8 ;
    $blue = $color & 0x0000FF ;printf('Red : %X (%d), Green : %X (%d), Blue : %X (%d)',
        $red, $red, $green, $green, $blue, $blue) ;// Will display...
    // Red : FE (254), Green : A9 (169), Blue : 46 (70)
?>

I recommend ALWAYS

(int)$var & (int)$var2

This will save you many headaches when troubleshooting a completely illogical result.

Actually, this is not an issue with the implementation of XOR,  but a lot more to do with the lose-typing policy that PHP adopts.

Freely switching between int and float is good for most cases, but problems happen when your value is near the word size of your machine. Which is to say, 32-bit machines will encounter problems with values that hover around 0x80000000 - primarily because PHP does not support unsigned integers.

using bindec/decbin would address this issue as a work-around to do unsigned-int xor, but here's the real picture (i'm not claiming that this code will perform better, but this would be a better pedagogical code):

<?phpfunction unsigned_xor32 ($a, $b)
{
        $a1 = $a & 0x7FFF0000;
        $a2 = $a & 0x0000FFFF;
        $a3 = $a & 0x80000000;
        $b1 = $b & 0x7FFF0000;
        $b2 = $b & 0x0000FFFF;
        $b3 = $b & 0x80000000;$c = ($a3 != $b3) ? 0x80000000 : 0;

        return ((

$a1 ^ $b1) |($a2 ^ $b2)) + $c;
}$x = 3851235679;
$y = 43814;
echo "<br>This is the value we want";
echo "<br>3851262585";

echo

"<br>The result of a native xor operation on integer values is treated as a signed integer";
echo "<br>".($x ^ $y);

echo

"<br>We therefore perform the MSB separately";
echo "<br>".unsigned_xor32($x, $y);?>

This is really foundation stuff, but for those of you who missed this in college, there seems to be something on 2's complement here:

http://www.evergreen.edu/biophysics/technotes/program/2s_comp.htm

place value   128  64  32  16   8  4   2   1
$a                     0      0    0     0    1  0   0   1   =9
$b                     0      0    0     0    1   0  1   0   =10

result   8 

only bit they share together is the 8 bit. So 8 gets returned.

  $a =     36;
$b =     103;
echo $a & $b;

place value   128  64  32  16   8    4   2   1
$a                     0      0    1     0    0    1   0   0   =36
$b                     0      1    1     0    0    1   1   1   =103

result  32+4 = 36
the only bits these two share together are the bits 32 and 4 which when added together return 36.

$a =     9;
$b =     10;
echo $a | $b;

place value   128  64  32  16   8  4   2   1
$a                     0      0    0     0    1  0   0   1   =9
$b                     0      0    0     0    1   0  1   0   =10

result 8+2+1 = 11
3 bits set, in the 8, 2, and 1 column.add those up 8+2+1 and you get 11

$a =     9;
$b =     10;
echo $a ^ $b;

place value   128  64  32  16   8  4   2   1
$a                     0      0    0     0    1  0   0   1   =9
$b                     0      0    0     0    1   0  1   0   =10

result  2+1 = 3
the 2 bit and the 1 bit that they each have set but don't share. Soooo 2+1 = 3

<?php
define("f0", 0x1); // 2^0
define("f1", 0x2); // 2^1
define("f2", 0x4); // 2^2
define("f3", 0x8); // 2^3
define("f4", 0x10); // 2^4
define("f5", 0x20); // 2^5
// ...
define("f20", 0x1000000); // 2^20
define("f21", 0x2000000); // 2^21
define("f22", 0x4000000); // 2^22
define("f23", 0x8000000); // 2^23
define("f24", 0x10000000); // 2^24
// ... up to 2^31
?>

I always avoid using decimal notation when I have a large amount of different flags, because it's very easy to misspell numbers like 2^20 (1048576).

$bin = 2;
$notbin = ~$bin;

echo "Bin: " . decbin($bin) . "  !bin:  " . decbin($notbin) . "n";

returns this:

Bin: 10  !bin:  1111111111111111111111111111111111111111111111111111111111111101

The reason is that all binary numbers are treated as 32 bits, even if you've manually entered less.  In order to get the result I expected (01), it was necessary to AND the result with the number of bits I wanted:  in this case, 2 (the number 3, in decimal).  Be aware that all return values will have zeros removed from the left until they reach a bit that is set to 1.  Continuing the above example, the following:

$notbin_2 = ~$bin & '3';
echo "!bin & 3:  " . decbin($notbin_2) . "n";

returns this:

!bin & 3:  1

Note that the actual value was a string of 31 zeros followed by a 1, but the zeros were not shown.  This is probably a good thing.

Furthermore, the NOT operator uses two's complement, which means the number you get may be even stranger than you expect:  using two's complement means that ~2 == -3.  There are plenty of good explanations of two's complement online, so I won't go into that question here.

If what you want is just to reverse a string of bits without any interpretation, you can use a function like this:

function bitnot($bin)
{
   $not = "";
   for ($i = 0; $i < strlen($bin); $i++)
   {
      if($bin[$i] == 0) { $not .= '1'; }
      if($bin[$i] == 1) { $not .= '0'; }
   }
   return $not;
}

It takes a binary string of any length, reverses the bits, and returns the new string.  You can then treat it as a binary number, use bindec() to turn it into a decimal, or whatever you want.

I hope this helps someone as much as it would have helped me a week ago!

Here is my solution for this: A class to store an array of integers being the bitmasks. It can hold up to 66571993087 bits, and frees up unused bitmasks when there are no bits being stored in them.

<?php
/*
    Infinite* bits and bit handling in general.

        *Not infinite, sorry.

        Perceivably, the only limit to the bitmask class in storing bits would be
    the maximum limit of the index number, on 32 bit integer systems 2^31 - 1,
    so 2^31 * 31 - 1 = 66571993087 bits, assuming floats are 64 bit or something.
    I'm sure that's enough enough bits for anything.. I hope :D.
*/

DEFINE('INTEGER_LENGTH',31); // Stupid signed bit.class bitmask
{
    protected $bitmask = array();

        public function

set( $bit ) // Set some bit
    {
        $key = (int) ($bit / INTEGER_LENGTH);
        $bit = (int) fmod($bit,INTEGER_LENGTH);
        $this->bitmask[$key] |= 1 << $bit;
    }

        public function

remove( $bit ) // Remove some bit
    {
        $key = (int) ($bit / INTEGER_LENGTH);
        $bit = (int) fmod($bit,INTEGER_LENGTH);
        $this->bitmask[$key] &= ~ (1 << $bit);
        if(!$this->bitmask[$key])
            unset($this->bitmask[$key]);
    }

        public function

toggle( $bit ) // Toggle some bit
    {
        $key = (int) ($bit / INTEGER_LENGTH);
        $bit = (int) fmod($bit,INTEGER_LENGTH);
        $this->bitmask[$key] ^= 1 << $bit;
        if(!$this->bitmask[$key])
            unset($this->bitmask[$key]);
    }

        public function

read( $bit ) // Read some bit
    {
        $key = (int) ($bit / INTEGER_LENGTH);
        $bit = (int) fmod($bit,INTEGER_LENGTH);
        return $this->bitmask[$key] & (1 << $bit);
    }

    public function

stringin($string) // Read a string of bits that can be up to the maximum amount of bits long.
    {
        $this->bitmask = array();
        $array = str_split( strrev($string), INTEGER_LENGTH );
        foreach( $array as $key => $value )
        {
            if($value = bindec(strrev($value)))
                $this->bitmask[$key] = $value;
        }
    }

    public function

stringout() // Print out a string of your nice little bits
    {
        $string = "";$keys = array_keys($this->bitmask);
        sort($keys, SORT_NUMERIC);

        for(

$i = array_pop($keys);$i >= 0;$i--)
        {
            if($this->bitmask[$i])
                $string .= sprintf("%0" . INTEGER_LENGTH . "b",$this->bitmask[$i]);
        }
        return $string;
    }

        public function

clear() // Purge!
    {
        $this->bitmask = array();
    }

        public function

debug() // See what's going on in your bitmask array
    {
        var_dump($this->bitmask);
    }
}
?>

It treats a positive integer input as a bit, so you don't have to deal with the powers of 2 yourself.

<?php
$bitmask = new bitmask();$bitmask->set(8979879); // Whatever$bitmask->set(888);

if(

$bitmask->read(888))
    print 'Happy!n';$bitmask->toggle(39393); // Yadda yadda$bitmask->remove(888);$bitmask->debug();$bitmask->stringin("100101000101001000101010010101010
00000001000001");

print

$bitmask->stringout() . "n";$bitmask->debug();$bitmask->clear();$bitmask->debug();
?>

Would produce:

Happy!

array(2) {
  [289673]=>
  int(65536)
  [1270]=>
  int(8388608)
}

0000000000000001001010001010010001010100101010100
0000001000001

array(2) {
  [0]=>
  int(355106881)
  [1]=>
  int(37970)
}

array(0) {
}

$x must be (int) when passing it to this function to work properly.

function comp2($x)      // 32bit bitwise complement
{
    $mask = 0x80000000;

    if ($x < 0)
    {
        $x &= 0x7FFFFFFF;
        $x = ~$x;

        return $x ^ $mask;
    }
    else
    {
        $x = $x ^ 0x7FFFFFFF;

        return $x | $mask;
    }
}

~2 = -3  because you use the formula  ~x = -x - 1  The bitwise complement of a decimal number is the negation of the number minus 1.

NOTE: just using 4 bits here for the examples below but in reality PHP uses 32 bits.

Converting a negative decimal number (ie: -3) into binary takes 3 steps:
1) convert the positive version of the decimal number into binary (ie: 3 = 0011)
2) flips the bits (ie: 0011 becomes 1100)
3) add 1 (ie: 1100  + 0001 = 1101)

You might be wondering how does 1101 = -3. Well PHP uses the method "2's complement" to render negative binary numbers. If the left most bit is a 1 then the binary number is negative and you flip the bits and add 1. If it is 0 then it is positive and you don't have to do anything. So 0010 would be a positive 2. If it is 1101, it is negative and you flip the bits to get 0010. Add 1 and you get 0011 which equals -3.

<?php

echo masksOf(3,10);

function

masksOf($n,$bits) {

    $u = pow(2,$bits)-1; //start value, full flags on.

    $masks = array();

    while ($u>0) {

        $z = numflags($u);

        if ($z==$n) array_push($masks,$u);

        $u--;

    }

    return ($masks);   

}

function

numflags($n) {

    $k = 0;

    while ($n) {

        $k += $n & 1;

        $n = $n >> 1;

    }

    return ($k);
//    alternately:

//    $u = 0;

//    for ($k=1;$k<=$n;$k*=2) {

//        $u+=($n&$k?1:0);

//    }

//    return ($u);

}

?>

(Note: It took me almost a whole day to get this to work with negative $num values (I couldn't figure out why it sometimes worked and other times didn't), because PHP only has an arithmatic and not a logical bitwise right shift like I am used to. I.e. 0x80000001>>16 will ouputs (in binary) "1111 1111 1111 1111 1000 0000 0000 0000" instead of "0000 0000 0000 0000 1000 0000 0000 0000" like you would expect. To fix this you have to apply the mask (by bitwise &) equal to 0x7FFFFFFF right shifted one less than the offset you are shifting by.)

<?php
function circular_shift($num,$offset) { //Do a nondestructive circular bitwise shift, if offset positive shift left, if negative shift right
    $num=(int)$num;
    $mask=0x7fffffff; //Mask to cater for the fact that PHP only does arithmatic right shifts and not logical i.e. PHP doesn't give expected output when right shifting negative values
    if ($offset>0) {
        $num=($num<<$offset%32) | (($num>>(32-$offset%32)) & ($mask>>(31-$offset%32)));
    }
    elseif ($offset<0){
        $offset=abs($offset);
        $num=(($num>>$offset%32) & ($mask>>(-1+$offset%32))) | ($num<<(32-$offset%32));
    }
    return $num;
}
?>

<?php
if (('18' & '32') == '10') {
    echo ord('18'); //return decimal value 49, which have binary value 110001
    echo ord('32'); //return decimal value 51, which have binary value 110011
    echo ord('10'); //return decimal value 49, which have binary value 110001
    //Therefore 110001 & 110011 = 110001
}
?>

here's a function to do logic right shifts.

<?phpfunction lshiftright($var,$amt)
{
    $mask = 0x40000000;
    if($var < 0)
    {
        $var &= 0x7FFFFFFF;
        $mask = $mask >> ($amt-1);
        return ($var >> $amt) | $mask;
    }
    return $var >> $amt;
}$val = -10;printf("arithmetic shift on a negative integer<br>%1$032b<br>%2$032b<br>%1$0d<br>%2$0d<br>",$val, $val >> 1 );printf("logic shift on a negative integer<br>%1$032b<br>%2$032b<br>%1$0d<br>%2$0d<br>",$val, lshiftright($val, 1));printf("logic shift on a positive integer<br>%1$032b<br>%2$032b<br>%1$0d<br>%2$0d<br>",-$val, lshiftright(-$val, 1));
?>

gives the output:

arithmetic shift on a negative integer
11111111111111111111111111110110
11111111111111111111111111111011
-10
-5

logic shift on a negative integer
11111111111111111111111111110110
01111111111111111111111111111011
-10
2147483643

logic shift on a positive integer
00000000000000000000000000001010
00000000000000000000000000000101
10
5

    protected function flipBin($number) {
        $bin = str_pad(base_convert($number, 10, 2), 32, 0, STR_PAD_LEFT);
        for ($i = 0; $i < 32; $i++) {
            switch ($bin{$i}) {
                case '0' :
                    $bin{$i} = '1';
                    break;
                case '1' :
                    $bin{$i} = '0';
                    break;
            }
        }
        return bindec($bin);
    }

the benefit is, it works with numbers greater MAX_INT

For example:

<?php
$foo = "1"; // chr(49)
var_dump($foo << 1); // Output is int(2)$foo = "!"; // chr(33)
var_dump($foo << 1); // Output is int(0)
?>

Here is the code:
<?php
function set_bitflag(/*variable-length args*/)
{
    $val = 0;
    foreach(func_get_args() as $flag) $val = $val | $flag;
    return $val;
}
function is_bitflag_set($val, $flag)
{
    return (($val & $flag) === $flag);
}
// Define your flags
define('MYFLAGONE', 1); // 0001
define('MYFLAGTWO', 2); // 0010
define('MYFLAGTHREE', 4); // 0100
define('MYFLAGFOUR', 8); // 1000
?>

I should point out: your flags are stored in a single integer. You can store loads of flags in a single integer.

To use my functions, say you wanted to set MYFLAGONE and MYFLAGTHREE, you would use:
<?php
$myflags = set_bitflags(MYFLAGONE, MYFLAGTHREE);
?>
Note: you can pass set_bitflags() as many flags to set as you want.

When you want to test later if a certain flag is set, use e.g.:
<?php
if(is_bitflag_set($myflags, MYFLAGTWO))
{
    echo "MYFLAGTWO is set!";
}
?>

The only tricky part is defining your flags. Here is the process:
1.  Write a list of your flags
2.  Count them
3.  Define the last flag in your list as 1 times 2 to the power of <count> minus one. ( I.E. 1*2^(<count>-1) )
3. Working backwards through your list, from the last to the first, define each one as half of the previous one. You should reach 1 when you get to the first

If you want to understand binary numbers, bits and bitwise operation better, the wikipedia page explains it well - http://en.wikipedia.org/wiki/Bitwise_operation.

After attempting to translate a Perl module into PHP, I realized that Perl's implementation of the ^ operator is different than the PHP implementation.  By default, Perl treats the variables as floats and PHP as integers.  I was able to verify the PHP use of the operator by stating "use integer;" within the Perl module, which output the exact same result as PHP was using.

The logical decision would be to cast every variable as (float) when using the ^ operator in PHP.  However, this will not yield the same results.  After about a half hour of banging my head against the wall, I discovered a gem and wrote a function using the binary-decimal conversions in PHP.

/*
not having much experience with bitwise operations, I cannot tell you that this is the BEST solution, but it certainly is a solution that finally works and always returns the EXACT same result Perl provides.
*/
function binxor($a, $b) {
    return bindec(decbin((float)$a ^ (float)$b));
}

//normal PHP code will not yeild the same result as Perl
$result = 3851235679 ^ 43814; //= -443704711

//to get the same result as Perl
$result = binxor(3851235679, 43814); //= 3851262585
//YIPPEE!!!

//to see the differences, try the following
$a = 3851235679 XOR 43814;
$b = 3851235679 ^ 43814; //integer result
$c = (float)3851235679 ^ (float)43814; //same as $b
$d = binxor(3851235679, 43814); //same as Perl!!

echo("A: $a<br />");
echo("B: $b<br />");
echo("C: $c<br />");
echo("D: $d<br />");

for example, you may want to check if the second bit is set:

<?php
if ($x & 2 == 2) {
    /* code */
}
?>

is different than

<?php
if (($x & 2) == 2) {
    /* code */
}
?>

and the latter of the two should be used.

<?php
var_dump(1234 ^ 0); // int(1234)
var_dump(1234 ^ ''); // int(1234)
var_dump(1234 ^ null); // int(1234)
var_dump('hello world' ^ 0); // int(0)
var_dump('hello world' ^ ''); // string(0) ""
var_dump('hello world' ^ null); // int(0)
?>

This seems rather inconsistent behavior. An integer XOR'd with zero results the original integer. But a string XOR'd with an empty value results an empty value!

My password hashing function was always returning the same hash... Because I was XOR-ing it with a salt that was sometimes empty!

So:
"18" is made up of two characters: 0x31, 0x38
"32" is made up of two characters: 0x33, 0x32
----RESULT-----
0x31 & 0x33 = 0x31 => "1"
0x38 & 0x32 = 0x30 => "0"

and the result is "10" which is 100% correct.

<?phpfunction setbit($v,$b=0){
        return (1<<$b)|$v;//($v&$x);
}

    echo

sprintf('%b', setbit(0b00000010,0));/*

bits position:          76543210
target number:  0b00000010
bit 0-------------------------^

so

bits position:          76543210
result:                      00000011
(sprintf will show  "11" value)
*/

?>

same results with anonymous functions from a constant! ..
<?php

define

('setbits',fn($v,$b=0)=>(1<<$b)|$v);
echo sprintf('%b',(setbits)(0b00000010,0));?>

all test i made are on last PHP Version => 8.2.4RC1 !

<?php
function count_set_bits( $n ){
  if( $n >= 0 ){  for( $count = 0;  $n;       ++$count )  $n &= $n - 1;  }
           else{  for( $count = 1;  $n << 1;  ++$count )  $n &= $n - 1;  }
  return $count;
}

echo

'This PHP uses ' . count_set_bits(-1) .'-bit integers.';
?>

    function reverse_bits($n) {
        return (int)base_convert(strrev(str_pad(base_convert($n, 10, 2), PHP_INT_SIZE * 8, 0, STR_PAD_LEFT)), 2, 10);
    }

Expect it to behave strangely for the signed bit. Best to use for < PHP_INT_SIZE * 8 to avoid peculiarity. You can also skip the cast if you don't mind keeping your number as a string. base convert appears to work for large precision or perhaps arbitrary but be prepared for strangeness (double, mixed types, precision loss, etc) if you need to work on the revolting number.

Use at your own peril.

Thanx for your great function. But your function is not 100% correct. It should be:

function safeBitCheck($number,$comparison) {
    if( $number < 2147483647 ) {
        return ($number & $comparison)==$comparison;  
    } else {
        $binNumber = strrev(base_convert($number,10,2));
        $binComparison = strrev(base_convert($comparison,10,2));
        for( $i=0; $i<strlen($binComparison); $i++ ) {
            if( strlen($binNumber) - 1 <$i || ($binComparison{$i}==="1" && $binNumber{$i}==="0") ) {
                return false;  
            }
        }
        return true;
    }
}

Mind the 'minus 1' on "if( strlen($binNumber) - 1 <$i".

cheers, Bart

<?phpfunction bitRotate32($value,$amount) {
    if ($amount>0) {
        $amount %= 32;
        $value = ($value<<$amount) | ($value>>(32-$amount));
    } elseif ($amount<0) {
        $amount = -$amount%32;
        $value = ($value>>$amount) | ($value<<(32-$amount));
    }
    return $value;
}

function

bitRotate($value,$amount,$bits) {
    $mask = ($bits<32) ? 0x7fffffff >> (31-$bits) : 0xffffffff;
    if ($amount>0) {
        $amount %= $bits;
        $value = ($value<<$amount) | ($value>>($bits-$amount));
    } elseif ($amount<0) {
        $amount = -$amount%$bits;
        $value = ($value>>$amount) | ($value<<($bits-$amount));
    }
    return $value & $mask;
}// test the rotation:$test = 4123;
for ($i=0; $i<64; $i++) {
    $value = bitRotate($test,-$i,8); // rotates 8 bits to the left (-$amount)
    echo sprintf("%032b<br/>",$value);
}?>

<?phpfunction hex2rgb($hex){$dec = hexdec($hexcolor);               // $hex string to decimal value
    $r = $dec & hexdec('FF0000');          //Mask for red
    $g = $dec & hexdec('00FF00');         //Mask for green
    $b = $dec & hexdec('0000FF');         //Mask for bluereturn array($r>>16, $g>>8, $b);       // Shift full right each color from its original position
}
?>

Example of use

<?php
$rgb = hex2rgb('112233');
echo "red: ".$rgb[0]."n";
echo "green: ".$rgb[1]."n";
echo "blue: ".$rgb[2]."n";
?>

Would produce:

red: 17       
green: 34
blue: 51

Since:
dechex(17) = '#11'
dechex(34) = '#22'
dechex(51) = '#33'

Don't forget the leading zeros.
It's very important if you want to write a function similar to the assembly instructions 'ror' and 'rol' (Rotate on Right and Rotate on Left), because of dword value; rotating the binary always takes 32 positions and includes the leading zeros!
So this is the right way:

<?phpfunction rotate ($decimal, $bits) {$binary = decbin($decimal);
  $binary = str_pad($binary, 32, '0', STR_PAD_LEFT);
  return (
    bindec(substr($binary, $bits).substr($binary, 0, $bits))
  );

}

?>

Look at this assembly code:

mov edx, 1bf5616c
ror edx, 8

After this operation: edx = 0x6c1bf561 (binary: 1101100000110111111010101100001)
But your code returns 0x0d9bf561 (binary: 1101100110111111010101100001)
In order to get the right value you have to add the leading zeros by adding that line with strpad() (see above). Very important!

// The result of the expression (false || true) is assigned to $e
// Acts like: ($e = (false || true))

$e = false || true;// The constant false is assigned to $f before the "or" operation occurs
// Acts like: (($f = false) or true)
$f = false or true;var_dump($e, $f);// --------------------
// "&&" has a greater precedence than "and"

// The result of the expression (true && false) is assigned to $g
// Acts like: ($g = (true && false))

For example:

$a = 0 || 'avacado';
print "A: $an";

will print:

A: 1

in PHP -- as opposed to printing "A: avacado" as it would in a language like Perl or JavaScript.

This means you can't use the '||' operator to set a default value:

$a = $fruit || 'apple';

instead, you have to use the '?:' operator:

$a = ($fruit ? $fruit : 'apple');

$a = ($fruit ?? 'apple');
//assigns the $fruit variable content to $a if the $fruit variable exists or has a value that is not NULL, or assigns the value 'apple' to $a if the $fruit variable doesn't exists or it contains the NULL value

var v = a || b || c || d;

I wrote a little helper method that I put in a function dump library (here presented as a bare function):

<?php
function either($a, $b){
        $val = $a ? $a : $b;
        /*
             Yes, I know the fixed parameters in the function
             are redundant since I could just use func_get_args,
             but in most instances I'll be using this a replacement
             for the ternary operator and only passing two values.
             I don't want to invoke the additional process below
             unless I REALLY have to.
        */
        $args = func_get_args();
        if($val === false && count($args) > 2){
            $args = array_slice($args, 2);

            foreach(

$args as $arg){
                if($arg !== false){
                    $val = $arg;
                    break;
                }
            }
        }
        return $val;
    }
?>

Now instead of:

$v = $a ? $a : $b;

I write:

$v = either($a, $b);

but more importantly, instead of writing:

$v = $a ? $a : ($b ? $b : $c);

I write:

$v = either($a, $b, $c);

or indeed:

$v = either($a, $b, $c, $d, $e, $f, $g, $h);

Instead of

$x ? $x : 'fallback'

you can also use the "elvis operator":

$x ?: 'fallback'

which is useful in cases, where the left-hand side of the ternary operator is too long type, is too complex to calculate twice, or has side-effects.

It also combines nicely with the ?? operator, which is equivalent to an empty() check (both isset() and `!= false`):

$x->y ?? null ?: 'fallback';

instead of:

empty($x->y) ? $x->y : 'fallback'

about the following example in this page manual:
Example#1 Logical operators illustrated

...
<?php
// "||" has a greater precedence than "or"
$e = false || true; // $e will be assigned to (false || true) which is true
$f = false or true; // $f will be assigned to false
var_dump($e, $f);// "&&" has a greater precedence than "and"
$g = true && false; // $g will be assigned to (true && false) which is false
$h = true and false; // $h will be assigned to true
var_dump($g, $h);
?>
_______________________________________________end of my quote...

If necessary, I wanted to give further explanation on this and say that when we write:
$f = false or true; // $f will be assigned to false
the explanation:

"||" has a greater precedence than "or"

its true. But a more acurate one would be

"||" has greater precedence than "or" and than "=", whereas "or" doesnt have greater precedence than "=", so

<?php
$f = false or true;//is like writting($f = false ) or true;//and$e = false || true;is the same as$e = (false || true);?>

same goes for "&&" and "AND".

If you find it hard to remember operators precedence you can always use parenthesys - "(" and ")". And even if you get to learn it remember that being a good programmer is not showing you can do code with fewer words. The point of being a good programmer is writting code that is easy to understand (comment your code when necessary!), easy to maintain and with high efficiency, among other things.

<?php
function a($x) { echo 'Expression '; return $x; }
function b($x) { echo 'is '; return $x; }
function c($x) { echo $x ? 'true.' : 'false.' ;}c( a( false ) and b( true ) ); // Output: Expression false.
c( min( a( false ), b( true ) ) ); // Output: Expression is false.c( a( true ) or b( true ) ); // Output: Expression true.
c( max( a( true ), b( true ) ) ); // Output: Expression is true.
?>

This way, values aren't automaticaly converted to boolean like it would be done when using and or or. Therefore, if you aren't sure the values are already boolean, you have to convert them 'by hand':

<?php
c( min( (bool) a( false ), (bool) b( true ) ) );
?>

<?php($a = $_GET['var']) || ($a = 'a default');?>

$a gets assigned $_GET['var'] if there's anything in it or it will fallback to 'a default'
Parentheses are required, otherwise you'll end up with $a being a boolean.

<?php
    // Defaults --

    //If you're trying to gat 'Jack' from:

$jack = false or 'Jack'; // Try:
    $jack = false or $jack = 'Jack';//The other option is:
    $jack = false ? false : 'Jack';
?>

NOTE: this is due to the first line actually being

($test = true) and false;

due to "&&" having a higher precedence than "=" while "and" has a lower one

<?php
$a = $fruit || 'apple'; //if $fruit evaluates to FALSE, then $a will be set to TRUE (because (bool)'apple' == TRUE)
?>

instead, you have to use the '?:' operator:

<?php
$a = ($fruit ? $fruit : 'apple');//if $fruit evaluates to FALSE, then $a will be set to 'apple'
?>

But $fruit will be evaluated twice, which is not desirable. For example fruit() will be called twice:
<?php
function fruit($confirm) {
    if($confirm)
        return 'banana';
}
$a = (fruit(1) ? fruit(1) : 'apple');//fruit() will be called twice!
?>

But since «since PHP 5.3, it is possible to leave out the middle part of the ternary operator» (http://www.php.net/manual/en/language.operators.comparison.php#language.operators.comparison.ternary), now you can code like this:

<?php
$a = ($fruit ? : 'apple'); //this will evaluate $fruit only once, and if it evaluates to FALSE, then $a will be set to 'apple'
?>

But remember that a non-empty string '0' evaluates to FALSE!

<?php
$fruit = '1';
$a = ($fruit ? : 'apple'); //this line will set $a to '1'
$fruit = '0';
$a = ($fruit ? : 'apple'); //this line will set $a to 'apple', not '0'!
?>

<?php
$v = my_function() or $v = "default";
?>

It works because, first, $v is assigned the return value from my_function(), then this value is evaluated as a part of a logical operation:
* if the left side is false, null, 0, or an empty string, the right side must be evaluated and, again, because 'or' has low precedence, $v is assigned the string "default"
* if the left side is none of the previously mentioned values, the logical operation ends and $v keeps the return value from my_function()

This is almost the same as the solution from [phpnet at zc dot webhop dot net], except that his solution (parenthesis and double pipe) doesn't take advantage of the "or" low precedence.

NOTE: "" (the empty string) is evaluated as a FALSE logical operand, so make sure that the empty string is not an acceptable value from my_function(). If you need to consider the empty string as an acceptable return value, you must go the classical "if" way.

JavaScript:
let a = false;
let b = false;
let c = true;
let d = false;
let e = a || b || c || d;
// e === c

<?PHP
$a = false;
$b = false;
$c = true;
$d = false;
$e = $a ?: $b ?: $c ?: $d;
// $e === $c
?>

Credit to @egst and others for the insight. This is merely a rewording for (formerly) lost JavaScript devs like myself.

for exemple :

unset($a);
if (    ($a < 0)   ||   (!isset($a))   )
echo 'Hello!';  

//      return error:  "Notice: Undefined variable: a "

unset($a);
if (    (!isset($a))   ||    ($a < 0)  )
echo 'Hello!';  

//      return   'Hello!'

practical example with an age check over 17 years:
if (    (!isset($age))   ||    ($age < 17)  )
$error_age = true;

this example will not display a php error if the age is not entered

$a = 0;
$b = 1;

printf('$a = %1$04b | $b = %2$04b ...  PROCESSED is: %3$s ( %3$04b )', $a, $b, ($a | $b));

<?php
$nc = true == false ?? 'no';
var_dump($nc); // false$nc = null ?? 'yes';
var_dump($nc); // yes$username = null == false ?? 'no';
var_dump($nc); // true$nc = $_GET['something'] ?? 'default';
var_dump($nc); // default$nc = !isset($_GET['something']) ?? 'wtf';
var_dump($nc); // true$nc = isset($_GET['something']) ?? 'wtf';
var_dump($nc); // false$_POST['second'] = 'chain';
$nc = $_GET['first'] ?? $_POST['second'] ?? $_REQUEST['third'] ?? 'wtf';
var_dump($nc); // chain
?>

$a = true;                  // true|false or something for test :)
$b = "I'm a string result"; // use|test `string` or `object`

if (!$a or !$c = $b) {
    $c = 'Hey';
}

// print result
var_dump($c); // "I'm a string result"

Have Fun!

e.g. if ($a=1 && $a>0)
will produce an unassigned error if $a has not previously been assigned a value.

<?php
isset($x) || $x = 123;

print

$x; // 123
?>



instead of:

<?php
if ( !isset($x)) {

    $x = 123;

}
// or
$x = isset($x) ? $x : 123;
// or
$x = isset($x) ?: 123;

?>



editor's note: In PHP 7 you could use the coalesce operator and do:

<?php

$x = $x ?? 123;

<?php
// do_that() is executed only if do_this() returns false
if($something) do_this() or do_that();
// $b is assigned to $b, do_that() is executed if $b is false
if($something) $a = $b or do_that();// do_that() is executed only if do_this() returns true
if($something) do_this() and do_that();
// $b is assigned to $b, do_that() is executed if $b is true
if($something) $a = $b and do_that();// both do_that() and do_this() are executed..
if($something) do_this() xor do_that();
// .. so the behaviour is same as:
if($something) {
    do_this();
    do_that();
}
?>

for understanding what happens if $b is NULL or do_this() returns NULL, read the avbentem's comment on NULL type. generaly speaking, NULL is threated like false in most cases.