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# L. GMP Functions

# 简介

These functions allow you to work with arbitrary-length integers using the GNU MP library.

These functions have been added in PHP 4.0.4.

> 注意: Most GMP functions accept GMP number arguments, defined as `resource` below. However, most of these functions will also accept numeric and string arguments, given that it is possible to convert the latter to a number. Also, if there is a faster function that can operate on integer arguments, it would be used instead of the slower function when the supplied arguments are integers. This is done transparently, so the bottom line is that you can use integers in every function that expects GMP number. See also the gmp_init() function.

警告
If you want to explicitly specify a large integer, specify it as a string. If you don't do that, PHP will interpret the integer-literal first, possibly resulting in loss of precision, even before `GMP` comes into play.

> 注意: This extension is available on Windows platforms since PHP 5.1.0.

# 需求

You can download the GMP library from http://www.swox.com/gmp/. This site also has the GMP manual available.

You will need GMP version 2 or better to use these functions. Some functions may require more recent version of the GMP library.

# 安装

In order to have these functions available, you must compile PHP with GMP support by using the `--with-gmp` option.

# 运行时配置

本扩展模块在 `php.ini` 中未定义任何配置选项。

# 资源类型

Most GPM functions operate on or return GMP number resources.

# 预定义常量

以下常量由本扩展模块定义，因此只有在本扩展模块被编译到 PHP 中，或者在运行时被动态加载后才有效。

`GMP_ROUND_ZERO` (integer)

`GMP_ROUND_PLUSINF` (integer)

`GMP_ROUND_MINUSINF` (integer)

# 范例

例 1. Factorial function using GMP

`<?php function fact($x) { $return = 1; for ($i=2; $i < $x; $i++) { $return = gmp_mul($return, $i); } return $return; } echo gmp_strval(fact(1000)) . "\n"; ?>`

This will calculate factorial of 1000 (pretty big number) very fast.

# 参见

More mathematical functions can be found in the sections BCMath Arbitrary Precision Mathematics Functions and Mathematical Functions.

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