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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。

位运算符
例子 名称 结果
$a & $b And(按位与) 将把 $a$b 中都为 1 的位设为 1。
$a | $b Or(按位或) 将把 $a$b 中任何一个为 1 的位设为 1。
$a ^ $b Xor(按位异或) 将把 $a$b 中一个为 1 另一个为 0 的位设为 1。
~ $a Not(按位取反) $a 中为 0 的位设为 1,反之亦然。
$a << $b Shift left(左移) $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) $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。

如果 &|^ 运算符的左右两个操作对象都是字符串,将对会组成字符串的字符 ASCII 值执行操作,结果也是一个字符串。除此之外,两个操作对象都将 转换为整数 ,结果也将会是整数。

如果 ~ 运算符的操作对象是字符串,则将对组成字符串的字符 ASCII 值进行操作, 结果将会是字符串,否则操作对象和结构都会是整数。

<<>> 运算符的操作对象和结果始终都是整数。

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
      

示例 #1 整数的 AND,OR 和 XOR 位运算符

<?php
/*
 * 忽略顶部,
 * 它只是为了使输出更加清晰而格式化。
 */

$format '(%1$2d = %1$04b) = (%2$2d = %2$04b)'
        
' %3$s (%4$2d = %4$04b)' "\n";

echo <<<EOH
 ---------     ---------  -- ---------
 result        value      op test
 ---------     ---------  -- ---------
EOH;


/*
 * 这是示例。
 */

$values = array(01248);
$test 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)

示例 #2 字符串的 XOR 运算符

<?php
echo 12 9// 输出 '5'

echo "12" "9"// 输出退格字符 (ascii 8)
                 // ('1' (ascii 49)) ^ ('9' (ascii 57)) = #8

echo "hallo" "hello"// 输出 ascii 值 #0 #4 #0 #0 #0
                        // 'a' ^ 'e' = #4

echo "3"// 输出 1
              // 2 ^ ((int)"3") == 1

echo "2" 3// 输出 1
              // ((int)"2") ^ 3 == 1
?>

示例 #3 整数的位移

<?php
/*
 * 这是示例。
 */

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');


/*
 * 忽略顶部,
 * 它只是为了使输出更加清晰而格式化。
 */

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
警告

使用 gmp 扩展对超出 PHP_INT_MAX 的数值来进行位操作。

参见

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