Mcrypt_list_algorithms() is used to get an array of all supported algorithms in the
lib_dir. Mcrypt_list_algorithms() takes as optional parameter a directory which specifies the directory where all algorithms are located. If not specifies, the value of the mcrypt.algorithms_dir php.ini directive is used.
The above example will produce a list with all supported algorithms in the "/usr/local/lib/libmcrypt" directory.