sudo apt install php7.0-gmp
Per potere utilizzare queste funzioni, occorre compilare il PHP con il supporto GMP utilizzando il parametro --with-gmp .
on Ubuntu Server:
sudo apt-get install libgmp-dev
sudo apt-get install php5-gmp
sudo service apache2 reload
Note that this parameter requires a path, as in --with-gmp=DIR, if gmp is installed in a non-standard location, which is almost always the case when you are building your own PHP installation in your home directory.
Obvious, but it's an easy mistake.
On ArchLinux php 5.4.14-1 I had to uncomment the line
in /etc/php/php.ini file.
Probably, restart of web server (e.g. Apache) is required if working from web.
Under Windows you will need to uncomment the line
within the php.ini and restart Apache.
on ubuntu you can get it from Synaptic Package Manager
just search words "gmp",you'll find it.
With PHP 5.3 on Windows, you need to use the VC9 build, otherwise you will not have the dll to enable GMP