PHPKonf: Istanbul PHP Conference 2017


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

gmp_initCrea un numero GMP


resource gmp_init ( mixed $number )

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

gmp_init (123456);
$b gmp_init ("0xFFFFDEBACDFEDF7200");


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 6 notes

marcus at synchromedia dot co dot uk
5 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.
php at richardneill dot org
10 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.

//Remove any leading zeros, or gmp_init will parse the number as octal.

if ($input==''){    //Deal with "0.0" which would otherwise be ''.
//exponent = (-)  the number of characters after the decimal point.
php at richardneill dot org
10 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.
karl dot debisschop at pearson dot com
5 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
charlie at oblivion dot cz
9 years ago
gmp_* functions don't accept strings with a leading '+':
echo gmp_strval(gmp_init('+42'));      #0
echo gmp_strval(gmp_add('42', '+42')); #42
echo bcadd('+42', '+42');              #84
thomas dot hebinck at digionline dot de
11 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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