PHPerKaigi 2021

gmp_init

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

gmp_initCreate GMP number

说明

gmp_init ( int|string $num , int $base = 0 ) : GMP

Creates a GMP number from an integer or string.

参数

num

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

base

The base.

The base may vary from 2 to 62. 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, if the first two characters are 0b or 0B, binary is assumed, otherwise if the first character is 0, octal is assumed, otherwise decimal is assumed. For bases up to 36, case is ignored; upper-case and lower-case letters have the same value. For bases 37 to 62, upper-case letter represent the usual 10 to 35 while lower-case letter represent 36 to 61.

返回值

GMP 对象。

范例

示例 #1 Creating GMP number

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

注释

注意:

It is not necessary to call this function in order to use integers or strings in place of GMP numbers in GMP functions (such as with 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

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3
php at richardneill dot org
14 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
marcus at synchromedia dot co dot uk
9 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
karl dot debisschop at pearson dot com
9 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
php at richardneill dot org
14 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
charlie at oblivion dot cz
14 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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-3
thomas dot hebinck at digionline dot de
15 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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