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gmp_init

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

gmp_initCrea un numero GMP

Descrizione

gmp_init(mixed $number): resource

Crea un numero GMP partendo da un intero o da una stringa. La stringa può essere decimale o esadecimale. Nell'ultimo caso, la stringa dovrebbe iniziare con 0x.

Example #1 Creare un numero GMP

<?php
$a
= gmp_init (123456);
$b = gmp_init ("0xFFFFDEBACDFEDF7200");
?>

Nota:

Non è necessario chiamare uesta funzione se si vogliono usare interi o stringhe al posto di numeri GMP nelle funzioni GMP, come gmp_add(). Se se questa conversione è possibile e necessaria, gli argomenti delle funzioni vengono automaticamente convertiti in numeri GMP, usando le stesse regole di gmp_init().

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User Contributed Notes 7 notes

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4
php at richardneill dot org
18 years ago
Here's a way to parse a decimal (eg 3.25) into an integer and exponent:

<?
if (preg_match("/^[0-9]+\.[0-9]+$/",$input)){
//Input is a base-10 decimal. Multiply as necessary to remove the decimal
//point. Convert that to a gmp_resource, then decrement the exponent
//to compensate.

$pieces=explode(".", $input); //Split at the d.p.
$input="$pieces[0]$pieces[1]"; //Remove the decimal point.

$input=ltrim($input,'0');
//Remove any leading zeros, or gmp_init will parse the number as octal.

if ($input==''){ //Deal with "0.0" which would otherwise be ''.
$input=0;
}
$integer=gmp_init($input);
$ns_exponent=-strlen($pieces[1]);
//exponent = (-) the number of characters after the decimal point.
}
?>
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2
karl dot debisschop at pearson dot com
13 years ago
Unless the base is 16, gpm_init will fail if the string begins with "0b".

> php -r '$v = gmp_init("b83", 17); print("$v\n");'

Resource id #4

> php -r '$v = gmp_init("0b83", 17); print("$v\n");'

[nothing prints]

In may case, where I am explicitly specifying the base, the solution is to apply ltrim first:

> php -r '$v = gmp_init(ltrim("0b83", "0"), 17); print("$v\n");'

Resource id #4
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2
marcus at synchromedia dot co dot uk
13 years ago
I discovered that the gmp functions use [0-9a-f] up to base 16, but [0-9A-Za-z] (i.e. upper case first) from bases 17 to 62. This differs from most of the base-62 implementations I've found that tend to use lower case first.
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1
php at richardneill dot org
18 years ago
Note: Leading zeros will make gmp_init parse this as octal.
Thus gmp_init(010) becomes 8.

$a=010; //8
$b="010" + 0; //10
$c=gmp_strval(gmp_init(010)); //8
$d=gmp_strval(gmp_init("010")); //8

This behaviour is inconsistent: either $d should equal $b, or
$b should equal $a.
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1
Aurelien Marchand
2 years ago
Missing from the documentation: gmp_init() return false in case it failed to parse $num

<?php
var_dump
(gmp_init(""));
// returns "bool(false)" and not a GMP object as hinted by the documentation, it also triggers a Warning "PHP Warning: gmp_init(): Unable to convert variable to GMP - string is not an integer in php shell code on line 1"

?>
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-1
charlie at oblivion dot cz
17 years ago
gmp_* functions don't accept strings with a leading '+':
<?php
echo gmp_strval(gmp_init('+42')); #0
echo gmp_strval(gmp_add('42', '+42')); #42
echo bcadd('+42', '+42'); #84
?>
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-2
thomas dot hebinck at digionline dot de
19 years ago
If you call a gmp_* function directly with an interger as parameter, this integer MUST NOT be 0:

for($i=-1;$i<=1;$i++) { echo gmp_strval(gmp_add(2,gmp_mul(1,$i))) . ' '; }

The result is 1 0 3 (wrong)

In this case you have to use gmp_init():

for($i=-1;$i<=1;$i++) { echo gmp_strval(gmp_add(2,gmp_mul(1,gmp_init($i)))) . ' '; }

The result is 1 2 3 (right)

Happy number crunching! :-)
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