gmp_setbit

(PHP 4 >= 4.0.4, PHP 5, PHP 7, PHP 8)

gmp_setbit — Set bit

说明

gmp_setbit(GMP $num, int $index, bool $value = true): void

Sets bit index in num.

参数

num: A GMP object.
index: The index of the bit to set. Index 0 represents the least significant bit.
value: True to set the bit (set it to 1/on); false to clear the bit (set it to 0/off).

返回值

没有返回值。

示例

示例 #1 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";
?>

以上示例会输出：

2 -> 0b10
3 -> 0b11

示例 #2 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";
?>

以上示例会输出：

253 -> 0b11111101
255 -> 0b11111111

示例 #3 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";
?>

以上示例会输出：

255 -> 0b11111111
254 -> 0b11111110

注释

注意:
Unlike most of the other GMP functions, gmp_setbit() must be called with a GMP object 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

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bluej100@gmail ¶

17 years ago

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
?>