位運算符 · PHP在線手冊

位運算符允許對整型數中指定的位進行求值和操作。 **位運算符** | 舉例 | 說明 | 詳細說明| | --- | --- | --- | | $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| 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| 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正負號不被保留。右移時左側以符號位填充，意味著正負號被保留。要用括號確保想要的優先級。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。要注意數據類型的轉換。如果左右參數都是字符串，則位運算符將對字符的 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實例子。要顯示除了提示級別之外的所有錯誤，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 然后通過 ~ 將其取反： 11111111111111111111111111110111 最后再用按位與 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 也可用來演示怎樣置位。只顯示錯誤和可恢復錯誤的方法是：E_ERROR | E_RECOVERABLE_ERROR >也就是將 E_ERROR 00000000000000000000000000000001 和 E_RECOVERABLE_ERROR 00000000000000000001000000000000 用按位或 OR（|）運算符來取得在任何一個值中被置位的結果： 00000000000000000001000000000001 ### 整數的 AND，OR 和 XOR 位運算符 ~~~ <?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); } ?> ~~~ 以上例程會輸出： 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 運算符 ~~~ <?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"; } ?> ~~~ 以上例程在 32 位機器上的輸出: ~~~ --- 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 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 位機器上的輸出: ~~~ --- 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 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 擴展對超出 PHP_INT_MAX 的數值來進行位操作。參見** pack()**，unpack()，gmp_and()，gmp_or()，gmp_xor()，gmp_testbit() 和 gmp_clrbit()。