位运算符允许对整型数中指定的位进行求值和操作。
**位运算符**
| 举例 | 说明 | 详细说明|
| --- | --- | --- |
| $a & $b | And（按位与）| 将把 $a 和 $b 中都为 1 的位设为 1。 |
| $a$b | Or（按位或） | 将把 $a 和 $b 中任何一个为 1 的位设为 1。 |
| $a ^ $b | Xor（按位异或） | 将把 $a 和 $b 中一个为 1 另一个为 0 的位设为 1。 |
| ~ $a |Not（按位取反） | 将 $a 中为 0 的位设为 1，反之亦然。 |
| $a << $b| 左移 | 将 $a 中的位向左移动 $b 次（每一次移动都表示“乘以 2”）。 |
| $a >> $b| 右移 | 将 $a 中的位向右移动 $b 次（每一次移动都表示“除以 2”）。|
位移在 PHP 中是数学运算。向任何方向移出去的位都被丢弃。左移时右侧以零填充，符号位被移走意味着正负号不被保留。右移时左侧以符号位填充，意味着正负号被保留。
要用括号确保想要的优先级。例如 $a & $b == true 先进行比较再进行按位与；而 ($a & $b) == true 则先进行按位与再进行比较。
要注意数据类型的转换。如果左右参数都是字符串，则位运算符将对字符的 ASCII 值进行操作。
PHP 的 ini 设定 error_reporting 使用了按位的值，
提供了关闭某个位的真实例子。要显示除了提示级别
之外的所有错误，php.ini 中是这样用的：E_ALL & ~E_NOTICE
~~~
具体运作方式是先取得 E_ALL 的值：
00000000000000000111011111111111
再取得 E_NOTICE 的值：
00000000000000000000000000001000
然后通过 ~ 将其取反：
11111111111111111111111111110111
最后再用按位与 AND（&）得到两个值中都设定了（为 1）的位：
00000000000000000111011111110111
~~~
另外一个方法是用按位异或 XOR（^）来取得只在
其中一个值中设定了的位：E_ALL ^ E_NOTICE
error_reporting 也可用来演示怎样置位。只显示错误和可恢复
错误的方法是：E_ERROR | E_RECOVERABLE_ERROR
>也就是将 E_ERROR
00000000000000000000000000000001
和 E_RECOVERABLE_ERROR
00000000000000000001000000000000
用按位或 OR（|）运算符来取得在任何一个值中被置位的结果：
00000000000000000001000000000001
### 整数的 AND，OR 和 XOR 位运算符
~~~
<?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);
}
?>
~~~
以上例程会输出：
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
--------- --------- -- ---------
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)
### 字符串的 XOR 运算符
~~~
<?php
echo 12 ^ 9; // Outputs '5'
echo "12" ^ "9"; // Outputs the Backspace character (ascii 8)
// ('1' (ascii 49)) ^ ('9' (ascii 57)) = #8
echo "hallo" ^ "hello"; // Outputs the ascii values #0 #4 #0 #0 #0
// 'a' ^ 'e' = #4
echo 2 ^ "3"; // Outputs 1
// 2 ^ ((int)"3") == 1
echo "2" ^ 3; // Outputs 1
// ((int)"2") ^ 3 == 1
?>
~~~
### 整数的位移
~~~
<?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";
}
?>
~~~
以上例程在 32 位机器上的输出:
~~~
--- 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
~~~
以上例程在 64 位机器上的输出:
~~~
--- 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
Warning
~~~
不要在 32 位系统下向右移超过 32 位。不要在结果可能超过 32 的情况下左移。使用 gmp 扩展对超出 PHP_INT_MAX 的数值来进行位操作。
参见** pack()**，unpack()，gmp_and()，gmp_or()，gmp_xor()，gmp_testbit() 和 gmp_clrbit()。
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