gmp_init

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

gmp_init — Create 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, octal, or binary.
base: The base to use for converting a string representation. An explicit base can be between 2 and 62. 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 values 10 to 35 and lower-case letter represent the values 36 to 61. If base is 0 then the actual base is determined from the leading characters of num. If the first two characters are 0x or 0X, the string is interpreted as a hexadecimal integer. If the first two characters are 0b or 0B, the string is interpreted as a binary integer. If the first two characters are 0o or 0o, the string is interpreted as an octal integer. Moreover, if the first character is 0 the string is also interpreted as an octal integer. In all other cases, the string is interpreted as a decimal integer.

返回值

GMP 对象。

更新日志

版本	说明
8.1.0	Support for explicit octal prefixes `0o` and `0o` has been added for `num` strings. Interpretation of such prefixes when `base` is `0` has also been added.

示例

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().

参见

GMP::__construct() - Create GMP number

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用户贡献的备注 7 notes

down

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.
}
?>

down

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

down

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.

down

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.

down

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"

?>

down

-1

charlie at oblivion dot cz ¶

18 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
?>

down

-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! :-)