gmp_setbit()

(PHP 4 >= 4.0.4, PHP 5, PHP 7)

Set bit

说明

gmp_setbit(GMP$a,int $index[,bool $bit_on= TRUE]): void

Sets bit$indexin$a.

参数

$a

The value to modify.

可以是一个 GMP数据resouce，或一个可以转换为数值的字符串。

$index

The index of the bit to set. Index 0 represents the least significant bit.

$bit_on

True to set the bit(set it to 1/on); false to clear the bit(set it to 0/off).

返回值

GMP 数值资源.

范例

gmp_setbit() example - 0 index

<?php
$a = gmp_init("2"); //
echo gmp_strval($a), ' -> 0b', gmp_strval($a, 2), "\n";
gmp_setbit($a, 0); // 0b10 now becomes 0b11
echo gmp_strval($a), ' -> 0b', gmp_strval($a, 2), "\n";
?>

以上例程会输出：

2 -> 0b10
3 -> 0b11

gmp_setbit() example - 1 index

<?php
$a = gmp_init("0xfd");
echo gmp_strval($a), ' -> 0b', gmp_strval($a, 2), "\n";
gmp_setbit($a, 1); // index starts at 0
echo gmp_strval($a), ' -> 0b', gmp_strval($a, 2), "\n";
?>

以上例程会输出：

253 -> 0b11111101
255 -> 0b11111111

gmp_setbit() example - clearing a bit

<?php
$a = gmp_init("0xff");
echo gmp_strval($a), ' -> 0b', gmp_strval($a, 2), "\n";
gmp_setbit($a, 0, false); // clear bit at index 0
echo gmp_strval($a), ' -> 0b', gmp_strval($a, 2), "\n";
?>

以上例程会输出：

255 -> 0b11111111
254 -> 0b11111110

注释

Note:

Unlike most of the other GMP functions,gmp_setbit() must be called with a GMP resource that already exists(using gmp_init() for example). One will not be automatically created.

参见

• gmp_clrbit()Clear bit
• gmp_testbit()Tests if a bit is set

The third parameter is somewhat confusingly named; it would probably be better described as "$set_state". If true, it sets the bit to 1. If false, it sets the bit to 0. Default is true.
<?php
$num = gmp_init(1);
gmp_setbit($num, 1);
echo 'gmp_setbit(1, 1): '.gmp_strval($num, 2)."\n"; // 11
$num = gmp_init(1);
gmp_setbit($num, 1, true);
echo 'gmp_setbit(1, 1, true): '.gmp_strval($num, 2)."\n"; // 11
$num = gmp_init(1);
gmp_setbit($num, 0, false);
echo 'gmp_setbit(1, 0, false): '.gmp_strval($num, 2)."\n"; // 0
?>