gmp_init

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

gmp_init — Create GMP number

说明

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

Creates a GMP number from an integer or string.

参数

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.

返回值

GMP 数值资源 .

更新日志

版本	说明
5.3.2	The `base` was extended from 2 to 36, to 2 to 62 and -2 to -36.

注释

Note:

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

范例

Example #1 Creating GMP number

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

注释

Note:

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() .

用户评论:

[#1] marcus at synchromedia dot co dot uk [2011-08-11 04:41:01]

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.

[#2] karl dot debisschop at pearson dot com [2011-03-29 12:15:46]

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

[#3] charlie at oblivion dot cz [2007-02-18 04:55:25]

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 ?>

[#4] php at richardneill dot org [2006-09-20 03:30:50]

Here's a way to parse a decimal (eg 3.25) into an integer and exponent:

<?php 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. } ?>

[#5] php at richardneill dot org [2006-09-20 03:14:00]

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.

[#6] thomas dot hebinck at digionline dot de [2005-08-18 10:23:06]

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! :-)