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PHP位运算符有哪些，使用要注意什么

lewis 1年前 (2024-03-31) 阅读数 6 #技术
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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和$b中都为 1 的位设为 1。 $a | $b Or（按位同或） 将把$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
/*
*Ignorethetopsection,
*itisjustformattingtomakeoutputclearer.
*/

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

echo<<<EOH
-----------------------------
resultvalueoptest
-----------------------------
EOH;

/*
*Herearetheexamples.
*/

$values=array(0,1,2,4,8);
$test=1+4;

echo"\nBitwiseAND\n";
foreach($valuesas$value){
$result=$value&$test;
printf($format,$result,$value,'&',$test);
}

echo"\nBitwiseInclusiveOR\n";
foreach($valuesas$value){
$result=$value|$test;
printf($format,$result,$value,'|',$test);
}

echo"\nBitwiseExclusiveOR(XOR)\n";
foreach($valuesas$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
echo12^9;//Outputs'5'

echo"12"^"9";//OutputstheBackspacecharacter(ascii8)
//('1'(ascii49))^('9'(ascii57))=#8

echo"hallo"^"hello";//Outputstheasciivalues#0#4#0#0#0
//'a'^'e'=#4

echo2^"3";//Outputs1
//2^((int)"3")==1

echo"2"^3;//Outputs1
//((int)"2")^3==1
?>

Example #3 整数的位移

<?php
/*
*Herearetheexamples.
*/

echo"\n---BITSHIFTRIGHTONPOSITIVEINTEGERS---\n";

$val=4;
$places=1;
$res=$val>>$places;
p($res,$val,'>>',$places,'copyofsignbitshiftedintoleftside');

$val=4;
$places=2;
$res=$val>>$places;
p($res,$val,'>>',$places);

$val=4;
$places=3;
$res=$val>>$places;
p($res,$val,'>>',$places,'bitsshiftoutrightside');

$val=4;
$places=4;
$res=$val>>$places;
p($res,$val,'>>',$places,'sameresultasabove;cannotshiftbeyond0');


echo"\n---BITSHIFTRIGHTONNEGATIVEINTEGERS---\n";

$val=-4;
$places=1;
$res=$val>>$places;
p($res,$val,'>>',$places,'copyofsignbitshiftedintoleftside');

$val=-4;
$places=2;
$res=$val>>$places;
p($res,$val,'>>',$places,'bitsshiftoutrightside');

$val=-4;
$places=3;
$res=$val>>$places;
p($res,$val,'>>',$places,'sameresultasabove;cannotshiftbeyond-1');


echo"\n---BITSHIFTLEFTONPOSITIVEINTEGERS---\n";

$val=4;
$places=1;
$res=$val<<$places;
p($res,$val,'<<',$places,'zerosfillinrightside');

$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,'signbitsgetshiftedout');

$val=4;
$places=(PHP_INT_SIZE*8)-2;
$res=$val<<$places;
p($res,$val,'<<',$places,'bitsshiftoutleftside');


echo"\n---BITSHIFTLEFTONNEGATIVEINTEGERS---\n";

$val=-4;
$places=1;
$res=$val<<$places;
p($res,$val,'<<',$places,'zerosfillinrightside');

$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,'bitsshiftoutleftside,includingsignbit');


/*
*Ignorethisbottomsection,
*itisjustformattingtomakeoutputclearer.
*/

functionp($res,$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。


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