php位元運算符

位元運算符允許對整型數中指定的位進行求值和操作。

位元運算符

例子 名稱 結果

$a & $b And（按位與） 將把 $a 和 $b 中都為 1 的位設為 1。

$a | $b Or（按位同或） 將把 $a 和 $b 中任何一個為 1 的位設為 1。

$a ^ $b Xor（按位異或） 將把 $a 和 $b 中一個為 1 另一個為 0 的位設為 1。

~ $a Not（按位取反） 將 $a 中為 0 的位設為 1，反之亦然。

$a << $b Shift left（左移） 將 $a 中的位向左移動 $b 次（每一次移動都表示“乘以 2”）。

$a >> $b Shift right（右移） 將 $a 中的位向右移動 $b 次（每一次移動都表示“除以 2”）。

位移在 PHP 中是數學運算。向任何方向移出去的位都被丟棄。左移時右側以零填充，符號位被移走意味著加號或減號不被保留。右移時左側以符號位填充，意味著加號或減號被保留。

要用括弧確保想要的優先順序。例如 $a & $b == true 先進行比較再進行按位與；而 ($a & $b) == true 則先進行按位與再進行比較。

要注意資料類型的轉換。如果左右參數都是字串，則位元運算符將對字元的 ASCII 值進行操作。
PHP 的 ini 設定 error_reporting 使用了按位的值，提供了關閉某個位的真執行個體子。要顯示除了提示層級之外的所有錯誤，php.ini 中是這樣用的：
E_ALL & ~E_NOTICE

具體運作方式是先取得 E_ALL 的值：00000000000000000111011111111111再取得 E_NOTICE 的值：00000000000000000000000000001000然後通過 ~ 將其取反：11111111111111111111111111110111最後再用按位與 AND（&）得到兩個值中都設定了（為 1）的位：00000000000000000111011111110111

另外一個方法是用按位異或 XOR（^）來取得只在
其中一個值中設定了的位：
E_ALL ^ E_NOTICE
error_reporting 也可用來示範怎樣置位。只顯示錯誤和可恢複
錯誤的方法是：
E_ERROR | E_RECOVERABLE_ERROR

也就是將 E_ERROR00000000000000000000000000000001和 E_RECOVERABLE_ERROR00000000000000000001000000000000用按位或 OR（|）運算子來取得在任何一個值中被置位的結果：00000000000000000001000000000001

Example #1 整數的 AND，OR 和 XOR 位元運算符

<?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);}?>

以上常式會輸出：

---------     ---------  -- --------- 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 字串的 XOR 運算子

<?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?>

Example #3 整數的位移

<?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";}?>

以上常式在 32 位元電腦上的輸出:

--- 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

以上常式在 64 位元電腦上的輸出:

--- 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 位系統下向右移超過 32 位。不要在結果可能超過 32 的情況下左移。使用 gmp 擴充對超出 PHP_INT_MAX 的數值來進行位操作。

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