PHP Australia Conference 2015

gmp_init

(PHP 4 >= 4.0.4, PHP 5)

gmp_initCreate GMP number

Descrierea

GMP gmp_init ( mixed $number [, int $base = 0 ] )

Creates a GMP number from an integer or string.

Parametri

number

An integer or a string. The string representation can be decimal, hexadecimal or octal.

base

The base.

The base may vary from 2 to 36. If base is 0 (default value), the actual base is determined from the leading characters: if the first two characters are 0x or 0X, hexadecimal is assumed, otherwise if the first character is "0", octal is assumed, otherwise decimal is assumed.

Valorile întoarse

Un număr GMP sub formă de resource în PHP 5.5 și anterior, sau obiect GMP în PHP 5.6 și ulterior.

Istoria schimbărilor

Versiunea Descriere
5.3.2 The base was extended from 2 to 36, to 2 to 62 and -2 to -36.

Note

Notă:

To use the extended base introduced in PHP 5.3.2, then PHP must be compiled against GMP 4.2.0 or greater.

Exemple

Example #1 Creating GMP number

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

Note

Notă:

It is not necessary to call this function if you want to use integer or string in place of GMP number in GMP functions, like gmp_add(). Function arguments are automatically converted to GMP numbers, if such conversion is possible and needed, using the same rules as gmp_init().

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User Contributed Notes 6 notes

up
1
marcus at synchromedia dot co dot uk
3 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.
up
0
karl dot debisschop at pearson dot com
3 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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0
charlie at oblivion dot cz
7 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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0
php at richardneill dot org
8 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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0
php at richardneill dot org
8 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.
up
-1
thomas dot hebinck at digionline dot de
9 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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