位运算符
位运算符允许对整型数中指定的位进行求值和操作。
| 例子 | 名称 | 结果 |
|---|---|---|
$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 | Shift left（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 | Shift right（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
Example #1 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：
--------- --------- -- --------- 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)
Example #2 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
?>
Example #3 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 sideExpression: 1 = 4 >> 2 Decimal: val=4 res=1 Binary: val=00000000000000000000000000000100 res=00000000000000000000000000000001Expression: 0 = 4 >> 3 Decimal: val=4 res=0 Binary: val=00000000000000000000000000000100 res=00000000000000000000000000000000 NOTE: bits shift out right sideExpression: 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 sideExpression: -1 = -4 >> 2 Decimal: val=-4 res=-1 Binary: val=11111111111111111111111111111100 res=11111111111111111111111111111111 NOTE: bits shift out right sideExpression: -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 sideExpression: 1073741824 = 4 << 28 Decimal: val=4 res=1073741824 Binary: val=00000000000000000000000000000100 res=01000000000000000000000000000000Expression: -2147483648 = 4 << 29 Decimal: val=4 res=-2147483648 Binary: val=00000000000000000000000000000100 res=10000000000000000000000000000000 NOTE: sign bits get shifted outExpression: 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 sideExpression: -2147483648 = -4 << 29 Decimal: val=-4 res=-2147483648 Binary: val=11111111111111111111111111111100 res=10000000000000000000000000000000Expression: 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 sideExpression: 1 = 4 >> 2 Decimal: val=4 res=1 Binary: val=0000000000000000000000000000000000000000000000000000000000000100 res=0000000000000000000000000000000000000000000000000000000000000001Expression: 0 = 4 >> 3 Decimal: val=4 res=0 Binary: val=0000000000000000000000000000000000000000000000000000000000000100 res=0000000000000000000000000000000000000000000000000000000000000000 NOTE: bits shift out right sideExpression: 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 sideExpression: -1 = -4 >> 2 Decimal: val=-4 res=-1 Binary: val=1111111111111111111111111111111111111111111111111111111111111100 res=1111111111111111111111111111111111111111111111111111111111111111 NOTE: bits shift out right sideExpression: -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 sideExpression: 4611686018427387904 = 4 << 60 Decimal: val=4 res=4611686018427387904 Binary: val=0000000000000000000000000000000000000000000000000000000000000100 res=0100000000000000000000000000000000000000000000000000000000000000Expression: -9223372036854775808 = 4 << 61 Decimal: val=4 res=-9223372036854775808 Binary: val=0000000000000000000000000000000000000000000000000000000000000100 res=1000000000000000000000000000000000000000000000000000000000000000 NOTE: sign bits get shifted outExpression: 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 sideExpression: -9223372036854775808 = -4 << 61 Decimal: val=-4 res=-9223372036854775808 Binary: val=1111111111111111111111111111111111111111111111111111111111111100 res=1000000000000000000000000000000000000000000000000000000000000000Expression: 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() 。