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
?>
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) . "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
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。