## Bitwise Operators

Bitwise operators allow evaluation and manipulation of specific bits within an integer.

Bitwise Operators
Example Name Result
`\$a & \$b` And Bits that are set in both \$a and \$b are set.
`\$a | \$b` Or (inclusive or) Bits that are set in either \$a or \$b are set.
`\$a ^ \$b` Xor (exclusive or) Bits that are set in \$a or \$b but not both are set.
`~ \$a` Not Bits that are set in \$a are not set, and vice versa.
`\$a << \$b` Shift left Shift the bits of \$a \$b steps to the left (each step means "multiply by two")
`\$a >> \$b` Shift right Shift the bits of \$a \$b steps to the right (each step means "divide by two")

Bit shifting in PHP is arithmetic. Bits shifted off either end are discarded. Left shifts have zeros shifted in on the right while the sign bit is shifted out on the left, meaning the sign of an operand is not preserved. Right shifts have copies of the sign bit shifted in on the left, meaning the sign of an operand is preserved.

Use parentheses to ensure the desired precedence. For example, \$a & \$b == true evaluates the equivalency then the bitwise and; while (\$a & \$b) == true evaluates the bitwise and then the equivalency.

If both operands for the &, | and ^ operators are strings, then the operation will be performed on the ASCII values of the characters that make up the strings and the result will be a string. In all other cases, both operands will be converted to integers and the result will be an integer.

If the operand for the ~ operator is a string, the operation will be performed on the ASCII values of the characters that make up the string and the result will be a string, otherwise the operand and the result will be treated as integers.

Both operands and the result for the << and >> operators are always treated as integers.

```PHP's error_reporting ini setting uses bitwise values,
providing a real-world demonstration of turning
bits off. To show all errors, except for notices,
the php.ini file instructions say to use:
`E_ALL & ~E_NOTICE`
```

```This works by starting with E_ALL:
00000000000000000111011111111111
Then taking the value of E_NOTICE...
00000000000000000000000000001000
... and inverting it via ~:
11111111111111111111111111110111
Finally, it uses AND (&) to find the bits turned
on in both values:
00000000000000000111011111110111
```

```Another way to accomplish that is using XOR (^)
to find bits that are on in only one value or the other:
`E_ALL ^ E_NOTICE`
```

```error_reporting can also be used to demonstrate turning bits on.
The way to show just errors and recoverable errors is:
`E_ERROR | E_RECOVERABLE_ERROR`
```

```This process combines E_ERROR
00000000000000000000000000000001
and
00000000000000000001000000000000
using the OR (|) operator
to get the bits turned on in either value:
00000000000000000001000000000001
```

Приклад #1 Bitwise AND, OR and XOR operations on integers

``` <?php/* * Ignore the top section, * it is just formatting to make output clearer. */\$format = '(%1\$2d = %1\$04b) = (%2\$2d = %2\$04b)'        . ' %3\$s (%4\$2d = %4\$04b)' . "\n";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 "\n Bitwise Exclusive OR (XOR) \n";foreach (\$values as \$value) {    \$result = \$value ^ \$test;    printf(\$format, \$result, \$value, '^', \$test);}?> ```

Наведений вище приклад виведе:

``` ---------     ---------  -- ---------
result        value      op test
---------     ---------  -- ---------
Bitwise AND
( 0 = 0000) = ( 0 = 0000) & ( 5 = 0101)
( 1 = 0001) = ( 1 = 0001) & ( 5 = 0101)
( 0 = 0000) = ( 2 = 0010) & ( 5 = 0101)
( 4 = 0100) = ( 4 = 0100) & ( 5 = 0101)
( 0 = 0000) = ( 8 = 1000) & ( 5 = 0101)

Bitwise Inclusive OR
( 5 = 0101) = ( 0 = 0000) | ( 5 = 0101)
( 5 = 0101) = ( 1 = 0001) | ( 5 = 0101)
( 7 = 0111) = ( 2 = 0010) | ( 5 = 0101)
( 5 = 0101) = ( 4 = 0100) | ( 5 = 0101)
(13 = 1101) = ( 8 = 1000) | ( 5 = 0101)

Bitwise Exclusive OR (XOR)
( 5 = 0101) = ( 0 = 0000) ^ ( 5 = 0101)
( 4 = 0100) = ( 1 = 0001) ^ ( 5 = 0101)
( 7 = 0111) = ( 2 = 0010) ^ ( 5 = 0101)
( 1 = 0001) = ( 4 = 0100) ^ ( 5 = 0101)
(13 = 1101) = ( 8 = 1000) ^ ( 5 = 0101)
```

Приклад #2 Bitwise XOR operations on strings

``` <?phpecho 12 ^ 9; // Outputs '5'echo "12" ^ "9"; // Outputs the Backspace character (ascii 8)                 // ('1' (ascii 49)) ^ ('9' (ascii 57)) = #8echo "hallo" ^ "hello"; // Outputs the ascii values #0 #4 #0 #0 #0                        // 'a' ^ 'e' = #4echo 2 ^ "3"; // Outputs 1              // 2 ^ ((int)"3") == 1echo "2" ^ 3; // Outputs 1              // ((int)"2") ^ 3 == 1?> ```

Приклад #3 Bit shifting on integers

``` <?php/* * Here are the examples. */echo "\n--- BIT SHIFT RIGHT ON POSITIVE 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);\$val = 4;\$places = 3;\$res = \$val >> \$places;p(\$res, \$val, '>>', \$places, 'bits shift out right side');\$val = 4;\$places = 4;\$res = \$val >> \$places;p(\$res, \$val, '>>', \$places, 'same result as above; can not shift beyond 0');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) . "b\n";    printf("Expression: %d = %d %s %d\n", \$res, \$val, \$op, \$places);    echo " Decimal:\n";    printf("  val=%d\n", \$val);    printf("  res=%d\n", \$res);    echo " Binary:\n";    printf('  val=' . \$format, \$val);    printf('  res=' . \$format, \$res);    if (\$note) {        echo " NOTE: \$note\n";    }    echo "\n";}?> ```

Наведений вище приклад на 32-бітних машинах виведе:

```
--- BIT SHIFT RIGHT ON POSITIVE INTEGERS ---
Expression: 2 = 4 >> 1
Decimal:
val=4
res=2
Binary:
val=00000000000000000000000000000100
res=00000000000000000000000000000010
NOTE: copy of sign bit shifted into left side

Expression: 1 = 4 >> 2
Decimal:
val=4
res=1
Binary:
val=00000000000000000000000000000100
res=00000000000000000000000000000001

Expression: 0 = 4 >> 3
Decimal:
val=4
res=0
Binary:
val=00000000000000000000000000000100
res=00000000000000000000000000000000
NOTE: bits shift out right side

Expression: 0 = 4 >> 4
Decimal:
val=4
res=0
Binary:
val=00000000000000000000000000000100
res=00000000000000000000000000000000
NOTE: same result as above; can not shift beyond 0

--- BIT SHIFT RIGHT ON NEGATIVE INTEGERS ---
Expression: -2 = -4 >> 1
Decimal:
val=-4
res=-2
Binary:
val=11111111111111111111111111111100
res=11111111111111111111111111111110
NOTE: copy of sign bit shifted into left side

Expression: -1 = -4 >> 2
Decimal:
val=-4
res=-1
Binary:
val=11111111111111111111111111111100
res=11111111111111111111111111111111
NOTE: bits shift out right side

Expression: -1 = -4 >> 3
Decimal:
val=-4
res=-1
Binary:
val=11111111111111111111111111111100
res=11111111111111111111111111111111
NOTE: same result as above; can not shift beyond -1

--- BIT SHIFT LEFT ON POSITIVE INTEGERS ---
Expression: 8 = 4 << 1
Decimal:
val=4
res=8
Binary:
val=00000000000000000000000000000100
res=00000000000000000000000000001000
NOTE: zeros fill in right side

Expression: 1073741824 = 4 << 28
Decimal:
val=4
res=1073741824
Binary:
val=00000000000000000000000000000100
res=01000000000000000000000000000000

Expression: -2147483648 = 4 << 29
Decimal:
val=4
res=-2147483648
Binary:
val=00000000000000000000000000000100
res=10000000000000000000000000000000
NOTE: sign bits get shifted out

Expression: 0 = 4 << 30
Decimal:
val=4
res=0
Binary:
val=00000000000000000000000000000100
res=00000000000000000000000000000000
NOTE: bits shift out left side

--- BIT SHIFT LEFT ON NEGATIVE INTEGERS ---
Expression: -8 = -4 << 1
Decimal:
val=-4
res=-8
Binary:
val=11111111111111111111111111111100
res=11111111111111111111111111111000
NOTE: zeros fill in right side

Expression: -2147483648 = -4 << 29
Decimal:
val=-4
res=-2147483648
Binary:
val=11111111111111111111111111111100
res=10000000000000000000000000000000

Expression: 0 = -4 << 30
Decimal:
val=-4
res=0
Binary:
val=11111111111111111111111111111100
res=00000000000000000000000000000000
NOTE: bits shift out left side, including sign bit
```

Наведений вище приклад на 64-бітних машинах виведе:

```
--- BIT SHIFT RIGHT ON POSITIVE INTEGERS ---
Expression: 2 = 4 >> 1
Decimal:
val=4
res=2
Binary:
val=0000000000000000000000000000000000000000000000000000000000000100
res=0000000000000000000000000000000000000000000000000000000000000010
NOTE: copy of sign bit shifted into left side

Expression: 1 = 4 >> 2
Decimal:
val=4
res=1
Binary:
val=0000000000000000000000000000000000000000000000000000000000000100
res=0000000000000000000000000000000000000000000000000000000000000001

Expression: 0 = 4 >> 3
Decimal:
val=4
res=0
Binary:
val=0000000000000000000000000000000000000000000000000000000000000100
res=0000000000000000000000000000000000000000000000000000000000000000
NOTE: bits shift out right side

Expression: 0 = 4 >> 4
Decimal:
val=4
res=0
Binary:
val=0000000000000000000000000000000000000000000000000000000000000100
res=0000000000000000000000000000000000000000000000000000000000000000
NOTE: same result as above; can not shift beyond 0

--- BIT SHIFT RIGHT ON NEGATIVE INTEGERS ---
Expression: -2 = -4 >> 1
Decimal:
val=-4
res=-2
Binary:
val=1111111111111111111111111111111111111111111111111111111111111100
res=1111111111111111111111111111111111111111111111111111111111111110
NOTE: copy of sign bit shifted into left side

Expression: -1 = -4 >> 2
Decimal:
val=-4
res=-1
Binary:
val=1111111111111111111111111111111111111111111111111111111111111100
res=1111111111111111111111111111111111111111111111111111111111111111
NOTE: bits shift out right side

Expression: -1 = -4 >> 3
Decimal:
val=-4
res=-1
Binary:
val=1111111111111111111111111111111111111111111111111111111111111100
res=1111111111111111111111111111111111111111111111111111111111111111
NOTE: same result as above; can not shift beyond -1

--- BIT SHIFT LEFT ON POSITIVE INTEGERS ---
Expression: 8 = 4 << 1
Decimal:
val=4
res=8
Binary:
val=0000000000000000000000000000000000000000000000000000000000000100
res=0000000000000000000000000000000000000000000000000000000000001000
NOTE: zeros fill in right side

Expression: 4611686018427387904 = 4 << 60
Decimal:
val=4
res=4611686018427387904
Binary:
val=0000000000000000000000000000000000000000000000000000000000000100
res=0100000000000000000000000000000000000000000000000000000000000000

Expression: -9223372036854775808 = 4 << 61
Decimal:
val=4
res=-9223372036854775808
Binary:
val=0000000000000000000000000000000000000000000000000000000000000100
res=1000000000000000000000000000000000000000000000000000000000000000
NOTE: sign bits get shifted out

Expression: 0 = 4 << 62
Decimal:
val=4
res=0
Binary:
val=0000000000000000000000000000000000000000000000000000000000000100
res=0000000000000000000000000000000000000000000000000000000000000000
NOTE: bits shift out left side

--- BIT SHIFT LEFT ON NEGATIVE INTEGERS ---
Expression: -8 = -4 << 1
Decimal:
val=-4
res=-8
Binary:
val=1111111111111111111111111111111111111111111111111111111111111100
res=1111111111111111111111111111111111111111111111111111111111111000
NOTE: zeros fill in right side

Expression: -9223372036854775808 = -4 << 61
Decimal:
val=-4
res=-9223372036854775808
Binary:
val=1111111111111111111111111111111111111111111111111111111111111100
res=1000000000000000000000000000000000000000000000000000000000000000

Expression: 0 = -4 << 62
Decimal:
val=-4
res=0
Binary:
val=1111111111111111111111111111111111111111111111111111111111111100
res=0000000000000000000000000000000000000000000000000000000000000000
NOTE: bits shift out left side, including sign bit
```

Увага

Shifting integers by values greater than or equal to the system long integer width results in undefined behavior. In other words, don't shift more than 31 bits on a 32-bit system, and don't shift more than 63 bits on a 64-bit system.

Use functions from the gmp extension for bitwise manipulation on numbers beyond PHP_INT_MAX.

### User Contributed Notes 34 notes

110
wbcarts at juno dot com
11 years ago
``` BITWISE FLAGS for Custom PHP ObjectsSometimes 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 8  public 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]?> ```
28
grayda dot NOSPAM at DONTSPAM dot solidinc dot org
14 years ago
``` Initially, I found bitmasking to be a confusing concept and found no use for it. So I've whipped up this code snippet in case anyone else is confused:<?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 ```
m0sh at hotmail dot com
15 years ago
``` @greenone - nice function, thanks. I've adapted it for key usage:<?phpfunction 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;}?> ```
16
18 years ago
``` A bitwise operators practical case :<?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)?> ```
10
frankemeks77 at yahoo dot com
11 years ago
``` Just learning Bitwise Shift Operators. 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 ```
zlel grxnslxves13 at hotmail dot com~=s/x/ee/g
18 years ago
``` I refer to Eric Swanson's post on Perl VS PHP's implementation of xor. 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 ```
zooly at globmi dot com
14 years ago
``` Here is an example for bitwise leftrotate and rightrotate.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 bitsecho rotate(124, -3);// = 79 (1001111)?> ```
zewt at hotmail dot com
16 years ago
``` if you use bitwise you MUST make sure your variables are integers, otherwise you can get incorrect results.I recommend ALWAYS(int)\$var & (int)\$var2This will save you many headaches when troubleshooting a completely illogical result. ```
Silver
14 years ago
``` Regarding what Bob said about flags, I'd like to point out there's a 100% safe way of defining flags, which is using hexadecimal notation for integers:<?phpdefine("f0", 0x1); // 2^0define("f1", 0x2); // 2^1define("f2", 0x4); // 2^2define("f3", 0x8); // 2^3define("f4", 0x10); // 2^4define("f5", 0x20); // 2^5// ...define("f20", 0x1000000); // 2^20define("f21", 0x2000000); // 2^21define("f22", 0x4000000); // 2^22define("f23", 0x8000000); // 2^23define("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). ```
vivekanand dot pathak25 at gmail dot com
10 years ago
``` \$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   =10result   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   =103result  32+4 = 36the 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   =10result 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   =10result  2+1 = 3the 2 bit and the 1 bit that they each have set but don't share. Soooo 2+1 = 3 ```
josh at joshstrike dot com
12 years ago
``` More referencing this for myself than anything... if you need to iterate through every possible binary combination where \$n number of flags are set to 1 in a mask of \$bits length: <?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); } ?> ```
Eric Swanson
18 years ago
``` Perl vs. PHP implementation of the ^ operator: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 />"); ```
cw3theophilus at gmail dot com
14 years ago
``` For those who are looking for a circular bit shift function in PHP (especially useful for cryptographic functions) that works with negtive values, here is a little function I wrote:(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.)<?phpfunction 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; }?> ```
icy at digitalitcc dot com
18 years ago
``` Say... you really want to have say... more than 31 bits available to you in your happy bitmask. And you don't want to use floats. So, one solution would to have an array of bitmasks, that are accessed through some kind of interface.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("10010100010100100010101001010101000000001000001");print \$bitmask->stringout() . "\n";\$bitmask->debug();\$bitmask->clear();\$bitmask->debug();?>Would produce:Happy!array(2) {  [289673]=>  int(65536)  [1270]=>  int(8388608)}00000000000000010010100010100100010101001010101000000001000001array(2) {  [0]=>  int(355106881)  [1]=>  int(37970)}array(0) {} ```
forlamp at msn dot com
15 years ago
``` two's complement logical operation for 32-bit.\$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;    }} ```
ivoras at gmail dot com
12 years ago
``` As an additional curiosity, for some reason the result of the operation ("18" & "32") is "10". In other words, try avoiding using the binary operators on strings :) ```
spencer-p-moy at example dot com
12 years ago
``` The NOT or complement operator ( ~ ) and negative binary numbers can be confusing.~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. ```
erich at seachawaii dot com
10 years ago
``` Just a note regarding negative shift values, as the documentation states each shift is an integer multiply or divide (left or right respectively) by 2.  That means a negative shift value (the right hand operand) effects the sign of the shift and NOT the direction of the shift as I would have expected.  FE. 0xff >> -2 results in 0x0 and 0xff << -2 result in 0xFFFFFFFFC0000000 (dependant on PHP_INT_MAX) ```
sag at ich dot net
10 years ago
``` me reimplement for bitwise NOT (~)    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 ```
aba at example dot com
12 years ago
``` It is true that if both the left-hand and right-hand parameters are strings, the bitwise operator will operate on the characters' ASCII values. However, a complement is necessary to complete this sentence.It is not irrelevant to point out that the decimal character's ASCII value have different binary values.<?phpif (('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}?> ```
amckenzie4 at gmail dot com
13 years ago
``` If, like me, you've never thought about how PHP deals with binary, the output of the bitwise NOT may confuse you.  For instance, this:\$bin = 2;\$notbin = ~\$bin;echo "Bin: " . decbin(\$bin) . "  !bin:  " . decbin(\$notbin) . "\n";returns this:Bin: 10  !bin:  1111111111111111111111111111111111111111111111111111111111111101The 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:  1Note 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! ```
Anonymous
13 years ago
``` Beware that PHP's << and >> operators, unlike the other bitwise operators do not work on ASCII values; << and >> cast their operands to integer (when possible) before shifting and will always return an integer result.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)?> ```
Tbrendstrup
18 years ago
``` note that the shift operators are arithmetic, not logic like in C. You may get unexpected results with negative numbers, see http://en.wikipedia.org/wiki/Bitwise_operationhere'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 integer1111111111111111111111111111011011111111111111111111111111111011-10-5logic shift on a negative integer1111111111111111111111111111011001111111111111111111111111111011-102147483643logic shift on a positive integer0000000000000000000000000000101000000000000000000000000000000101105 ```
Core Xii
13 years ago
``` Be very careful when XOR-ing strings! If one of the values is empty (0, '', null) the result will also be empty!<?phpvar_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! ```
13 years ago
``` Be careful of order of operations.for example, you may want to check if the second bit is set:<?phpif (\$x & 2 == 2) {    /* code */}?>is different than<?phpif ((\$x & 2) == 2) {    /* code */}?>and the latter of the two should be used. ```
Anonymous
12 years ago
``` To make very clear why ("18" & "32") is "10".1) they they are both strings ,2) "&" operator works on strings by taking each !Character! from each string and make a bit wise & between them and add this value to the resulting stringSo:"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. ```
biziclop at vipmail dot hu
4 years ago
``` A fast algorithm (Brian Kernighan's) to count all bits set to 1 in an integer, modified to work with signed ints.It does the same as https://php.net/gmp_popcount except for ordinary integers.<?phpfunction 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.';?> ```
ASchmidt at Anamera dot net
4 years ago
``` Setting, unsetting and testing single and multiple bits in a bitmask:<?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) ```
joey
7 years ago
``` If you want a quick one liner for reversing binary and performance/sanity isn't an issue:    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. ```
luis at rosety dot com
8 years ago
``` Example of function using bitwise operations for converting hexadecimal color (usually given as 6 hexadecimal digit string, into separated RGB integers)<?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 blue    return 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: 34blue: 51Since:dechex(17) = '#11'dechex(34) = '#22'dechex(51) = '#33' ```
Bob
14 years ago
``` Here is an easy way to use bitwise operation for 'flag' functionality.By this I mean managing a set of options which can either be ON or OFF, where zero or more of these options may be set and each option may only be set once. (If you are familiar with MySQL, think 'set' datatype).Note: to older programmers, this will be obvious.Here is the code:<?phpfunction 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 flagsdefine('MYFLAGONE', 1); // 0001define('MYFLAGTWO', 2); // 0010define('MYFLAGTHREE', 4); // 0100define('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.:<?phpif(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 flags2.  Count them3.  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 firstIf you want to understand binary numbers, bits and bitwise operation better, the wikipedia page explains it well - http://en.wikipedia.org/wiki/Bitwise_operation. ```
bartbons at debster.nl
15 years ago
``` @kendsnyder at gmail dot comThanx 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 ```
Nina Cording
18 years ago
``` For those who were searching for a way to actually rotate the bits of a number, here are some little functions I wrote:<?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);}?> ```
-4
J. Ketting
9 years ago
``` @zoolyDon'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, 1bf5616cror edx, 8After 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! ```