Haroldo,
Pode ser que ele queira o GMP para outra coisa.
Veja que o GMP é indicado para:
Criptografia, segurança de aplicações para internet, sistemas de computação algébrico ou mesmo para testar algoritmos
O módulo php5-gmp é somente uma ponte para usar o GMP.
What is GMP?
GMP is a free library for arbitrary precision arithmetic, operating on signed integers, rational numbers, and floating-point numbers. There is no practical limit to the precision except the ones implied by the available memory in the machine GMP runs on. GMP has a rich set of functions, and the functions have a regular interface.
The main target applications for GMP are cryptography applications and research, Internet security applications, algebra systems, computational algebra research, etc.
GMP is carefully designed to be as fast as possible, both for small operands and for huge operands. The speed is achieved by using fullwords as the basic arithmetic type, by using fast algorithms, with highly optimised assembly code for the most common inner loops for a lot of CPUs, and by a general emphasis on speed.
The first GMP release was made in 1991. It is continually developed and maintained, with a new release about once a year.
Since version 6, GMP is distributed under the dual licenses, GNU LGPL v3 and GNU GPL v2. These licenses make the library free to use, share, and improve, and allow you to pass on the result. The GNU licenses give freedoms, but also set firm restrictions on the use with non-free programs.
GMP is part of the GNU project. For more information about the GNU project, please see the official GNU web site.
GMP’s main target platforms are Unix-type systems, such as GNU/Linux, Solaris, HP-UX, Mac OS X/Darwin, BSD, AIX, etc. It also is known to work on Windows in both 32-bit and 64-bit mode.
GMP is brought to you by a team listed in the manual.
GMP is carefully developed and maintained, both technically and legally. We of course inspect and test contributed code carefully, but equally importantly we make sure we have the legal right to distribute the contributions, meaning users can safely use GMP. To achieve this, we will ask contributors to sign paperwork where they allow us to distribute their work.