const

 The const data-type qualifier restricts access to stored data.  If
 you declare an object to be of type const, you cannot modify that
 object.  You can use the const data-type qualifier with the
 volatile data-type qualifier or with any of the storage-class
 specifiers or modifiers.  The following example declares the
 variable x to be a constant integer:

      int const x;


volatile

 The volatile data-type qualifier prevents an object from being
 stored in a machine register, forcing it to be allocated in memory.
 This data-type qualifier is useful for declaring data that is to be
 accessed asynchronously.  A device driver application often uses
 volatile data storage.  Like const, you can specify the volatile
 data-type qualifier with any of the storage-class specifiers or
 modifiers with the exception of the register storage class.


__restrict

 The __restrict data-type qualifier is used to designate a pointer
 as pointing to a distinct object, thus allowing compiler
 optimizations to be made.


__unaligned

 This data-type qualifier is used in pointer definitions, indicating
 to the compiler that the data pointed to is not properly aligned on
 a correct address.  (To be properly aligned, the address of an
 object must be a multiple of the size of the type.  For example,
 two-byte objects must be aligned on even addresses.) When data is
 accessed through a pointer declared __unaligned, the compiler
 generates the additional code necessary to copy or store the data
 without causing alignment errors.  It is best to avoid use of
 misaligned data altogether, but in some cases the usage may be
 justified by the need to access packed structures, or by other
 considerations.