位运算符¶

位运算符允许对整型数中指定的位进行置位。如果左右参数都是字符串，则位运算符将操作字符的 ASCII 值。

<?php echo 12 ^ 9; // 输出为 ‘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 2 ^ “3”; // 输出 1: // 2 ^ ((int)”3”) == 1
echo “2” ^ 3; // 输出 1: // ((int)”2”) ^ 3 == 1

?> 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（按位或）将把 $a 或者 $b 中为 1 的位设为 1。 $a ^ $b Xor（按位异或）将把 $a 和 $b 中不同的位设为 1。 ~ $a Not（按位非）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”）。 Example #1 Bit shifting on integers <?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) . “bn”;

printf(“Expression: %d = %d %s %dn”, $res, $val, $op, $places);

echo ” Decimal:n”; printf(” val=%dn”, $val); printf(” res=%dn”, $res);

echo ” Binary:n”; printf(‘ val=’ . $format, $val); printf(‘ res=’ . $format, $res);

if ($note) {: echo ” NOTE: $noten”;

}

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 在 32 位系统上不要右移超过 32 位。不要在结果可能超过 32 位的情况下左移。