The first prototype is when linked against libmcrypt
2.2.x, the second when linked against libmcrypt 2.4.x or
2.5.x.
mcrypt_get_block_size() is used
to get the size of a block of the specified cipher (in combination with an
encryption mode).
This example shows how to use this function when linked
against libmcrypt 2.4.x and 2.5.x.
See also: mcrypt_get_key_size() and
mcrypt_encrypt().