GMP Functions
PHP Manual

gmp_setbit

Set bit

Description

void gmp_setbit ( resource &$a , int $index [, bool $bit_on = true ] )

Sets bit index in a.

Parameters

a

The value to modify.

It can be either a GMP number resource, or a numeric string given that it is possible to convert the latter to a number.

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).

Return Values

A GMP number resource.

Examples

Example #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";
?>

The above example will output:

2 -> 0b10
3 -> 0b11

Example #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";
?>

The above example will output:

253 -> 0b11111101
255 -> 0b11111111

Example #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";
?>

The above example will output:

255 -> 0b11111111
254 -> 0b11111110

Notes

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.

See Also

  • gmp_clrbit
  • gmp_testbit